Place your hand on your chest, or feel your pulse, while breathing calmly in and out. If you pay close attention, you may notice that your heart rate subtly speeds up as you inhale and slows down as you exhale. This rhythmic pattern, entirely natural yet usually unnoticed, is called respiratory sinus arrhythmia, abbreviated RSA.

The term may sound technical, even alarming (“arrhythmia”1 [1] means “no (= a) rhythm” and suggests a heart rhythm disorder), but RSA is actually a sign of good health. It reflects the smooth cooperation between your breathing and your heart function, with the vagus nerve as the connecting link: the long, branching nerve that runs from your brainstem downward and innervates2 your heart, lungs, and many other organs.

Where heart rate variability (HRV) offers a broad window onto the total variability in your heart rate, respiratory sinus arrhythmia is more specific and more precise. RSA measures the direct influence of the ventral vagus: the fast, myelinated pathway of the vagus nerve that, in mammals, sits at the center of a system for social engagement, flexibility, and resilience.

In this article I’ll take you through the world of RSA: what it is, how it arises, why it matters so much for your health and wellbeing, how it’s measured, and how it sits at the heart of polyvagal theory, the framework that has transformed our understanding of trauma, connection, and recovery.

RSA in a nutshell

In this section I tell the story of RSA in an accessible form, suitable and sufficiently detailed for most readers: what it is, how it arises, what it says about your health, and how you can strengthen it. Readers who are eager to know more about the technical and scientific background will find that further on, in the deep-dive section.

What is respiratory sinus arrhythmia?

The definition: breathing and heartbeat in harmony

RSA is the natural, rhythmic variation in heart rate that runs in sync with the breathing cycle. During inhalation, your heart rate speeds up slightly. During exhalation, it slows down again. This rise and fall is not a coincidence or a malfunction, but a beautiful example of how your body continuously optimizes and synchronizes itself.

The word “arrhythmia” in the term can be confusing. In medical usage, arrhythmia denotes a (sometimes problematic) irregularity in heart rhythm. But the “sinus arrhythmia” in RSA refers to a healthy, functional variation. The heartbeat simply originates in the sinoatrial node, the heart's natural pacemaker, but its tempo is rhythmically adjusted via the vagus nerve, in time with breathing. The word “sinus” signals precisely that the beats continue to come from that pacemaker as normal, and it is that fact which distinguishes this harmless variation from a true rhythm disorder. RSA is therefore not a disorder at all, but a sign of a well-functioning, flexible autonomic nervous system.

Making the pattern felt

Try it yourself: sit or lie down quietly, place your hand on your chest or feel your pulse, and breathe slowly and deeply. Inhale for about four to five counts, exhale for about six to eight. You’ll notice that your heart rate subtly but perceptibly speeds up as you inhale and slows down as you exhale. That’s your RSA in action.

The amplitude of that fluctuation, the difference between the fastest and the slowest heart rate within a breathing cycle, averaged across several breaths, says something about the strength and flexibility of your vagal regulation. A larger amplitude points to more flexible vagal tone, a measure of the “fitness” of your nervous system. A small amplitude, or the absence of RSA, can point to reduced vagal function.

How does RSA arise?

RSA is not a passive byproduct of breathing; it is the result of a finely tuned interplay in the brainstem that couples breathing and heart function. Two elements are enough to grasp the essentials: the role of breathing and the role of the ventral vagus. The brainstem network that fine-tunes this coupling is described in the deep-dive section toward the end of this article.

The role of breathing

During inhalation, your chest expands and the pressure in your chest cavity drops. Besides drawing air in, this also pulls more blood from the veins toward the heart, giving the heart more blood to work with. At the same time, sensors in the lungs and blood vessels send a signal to the brainstem: the heart rate may rise slightly. During exhalation this reverses: pressure rises again, less blood flows back, and the heart rate falls.

At first glance this looks purely mechanical. But the real control lies in the nervous system. Not in the nerve fibers themselves; a nerve fiber doesn’t generate the signal itself, it conducts it: the rhythm originates in neurons located in the brainstem and reaches the heart via the vagus nerve.

The ventral vagus: the fast pathway to the heart

The vagus nerve is the tenth cranial nerve, one of the longest and most extensively branching nerves in the body. Within that nerve, fibers of two different origins run intertwined3. The ventral vagus consists of myelinated (insulated) fibers that originate in the nucleus ambiguus and conduct quickly; they innervate the heart, the larynx, and other structures above the diaphragm. The dorsal vagus consists of slower, unmyelinated fibers and mainly innervates organs below the diaphragm, such as the stomach, intestines, liver, and pancreas.

RSA arises through the ventral vagus. During exhalation, the neurons in the nucleus ambiguus fire most strongly, applying the vagal brake to the heart and slowing the heart rate. During inhalation, that vagal brake eases, a phenomenon known as “inspiratory gating,” allowing the heart rate to rise. RSA is therefore not a mechanical reflex but an actively regulated rhythm that finely coordinates breathing and heart function.

RSA and HRV: what’s the difference?

Heart rate variability (HRV) is a broad concept: all variation over time between successive heartbeats, regardless of cause. Breathing, blood pressure regulation, temperature, hormones, and emotion all contribute to it. Think of it as the total sound of an orchestra. Respiratory sinus arrhythmia is one specific component within that: the breathing-linked variation, which mainly reflects regulation by the ventral vagus. If HRV is the orchestra, RSA is the solo violin. For the full picture on HRV, the metrics involved, and its meaning for our health, see my in-depth Relaxicon article on HRV.

Why does this distinction matter? A general measure like HRV bundles all those influences (the whole orchestra) into a single number, without separating them out. A high value can point to healthy vagal flexibility, but it can just as easily reflect other factors. RSA isolates the ventral vagal component and so provides more targeted information about how smoothly that ventral vagal system specifically is working, the system that supports social engagement, safety, and resilience.

RSA and polyvagal theory

Polyvagal theory (Porges, 1995, 2007) places RSA within an evolutionary and neurobiological framework. Its core idea is that the autonomic nervous system consists not of two, but of three hierarchically ordered systems.

The oldest is the dorsal vagal complex, which supports metabolic recovery and rest and, under overwhelming threat, can lead to immobilization or “shutdown.” Above that sits the sympathetic nervous system, which supports mobilization: being active, or fight-and-flight behavior under threat. In the theory’s layered structure, this system is younger than the dorsal vagus and older than the ventral vagus. The newest, in terms of the integration seen in mammals, is the ventral vagal complex, which supports social engagement, communication, and co-regulation, and which generates RSA.

These systems operate according to a simple logic. When the body feels safe, the ventral system dominates: you are socially accessible, your voice carries melody, your face is expressive. This is sometimes called the “green zone.” When the ventral system withdraws under threat, sympathetic mobilization takes over, the “yellow zone” of action and alertness. If that doesn’t help either, for example under overwhelming threat with no way out, the dorsal system comes to dominate: immobilization and dissociation, the “red zone.”

RSA as a marker of safety

Within this hierarchy, RSA functions as a real-time signal of ventral vagal activity. The amplitude of that fluctuation (see above) reflects the strength and flexibility of your vagal regulation.

Low or absent RSA points to reduced activity in that system and to a more defensive or mobilized state. This carries implications for therapy, education, and parenting: someone showing low RSA is, physiologically, not in the best possible state to connect or to learn. Interventions that foster safety and ventral vagal activation can help shift that.

Does RSA still serve a function in us?

Here comes a surprising fact that may challenge your intuition a little. The breathing-linked variation in heart rate is ancient, predating mammals by hundreds of millions of years. In animals without fully separated pulmonary and systemic circulation, such as amphibians and most reptiles, and in fish with their gill-based breathing, RSA does important work: the fluctuation helps direct blood efficiently past the respiratory organs (gills or lungs) with each breath.

Mammals no longer need that efficiency gain, because our hearts have fully separated chambers for the pulmonary and systemic circulations. In mammals, then, RSA is not really an evolutionary innovation, nor a functional mechanism anymore, but a holdover from a time when the rhythm still had real work to do. I’ve explored this in depth in the article “How Old Is That Ventral Vagus, Really?”

But if RSA has lost its original function in us, why is it still considered a marker of health? Because for us, its value lies not in what it does, but in what it reveals. The variation arises because the heart is continuously fine-tuned, moment to moment, via the fast ventral vagal fibers. The magnitude of that fluctuation is therefore a window onto how smoothly that regulation is working. High variability points to a flexible, responsive system; low variability points to a system faltering under stress, illness, or age. In mammals, RSA is no longer a functional mechanism, but it remains a useful and measurable signal, and that is precisely where its value lies.

RSA across the lifespan

RSA is measurable even before birth, in fetal heart rate patterns. The fetus is not yet breathing air, but does make rhythmic breathing movements, and RSA is visible in the heart rate during those episodes4 (Divon et al., 1985). Reed, Ohel, David, and Porges (1999) showed that low RSA, a sign of low ventral vagal tone, precedes and is associated with vulnerability to life-threatening bradycardia during labor; strong ventral vagal tone, by contrast, appears protective. In newborns, baseline RSA predicts autonomic reactivity and developmental outcomes; premature infants consistently show lower RSA. Interventions such as skin-to-skin contact and a soft, melodic voice can raise it.

In children, higher RSA is associated with better attention, emotion regulation, and social skills. A healthy “RSA suppression,”5 in which RSA temporarily drops during a challenge and then recovers, points to flexibility; a failure to recover can point to rigidity.

Respiratory sinus arrhythmia declines with age. That decline is not linear: on average it is steepest in early adulthood and levels off afterward. This decline can be influenced by behavior: people who exercise regularly, sleep well, manage stress, and maintain social connections retain more autonomic flexibility later in life.

RSA and health

RSA carries signal value across a wide range of contexts. In cardiology, low RSA predicts elevated risk of cardiovascular disease and a poorer prognosis after a heart attack, while RSA recovery after rehabilitation is a favorable sign.

In mental health care, reduced RSA is commonly seen in anxiety, depression, and post-traumatic symptoms. This fits with a chronically “withdrawn” ventral system and a less flexible autonomic state that is less accessible to connection and relaxation. Treatments that raise vagal tone, from psychotherapy to movement and breathwork, are often accompanied by an increase in RSA and by symptom improvement (Lehrer et al., 2020; Goessl et al., 2017). Reduced RSA has also been described in functional conditions such as irritable bowel syndrome, chronic fatigue, and fibromyalgia (Meeus et al., 2013; Escorihuela et al., 2020).

For athletes, RSA helps with dosing training and recovery: a high value points to recovery and capacity for load, a declining value to possible overtraining. Faster RSA recovery after exertion is a sign of good autonomic flexibility and cardiovascular fitness.

Strengthening RSA: what can you do?

The good news is that RSA can be influenced. The most direct route is slow, deep breathing. Breathing at your so-called resonance frequency improves your RSA amplitude. That frequency differs from person to person but for most people lies around five to six breaths per minute (it depends partly on body build and on the timing of your baroreflex). A simple exercise: inhale for four to five seconds through your nose and exhale for six to eight seconds, repeated for five to ten minutes a day. The longer exhale strengthens vagal activity and directly raises RSA. HRV biofeedback, in which you guide your breathing rhythm using real-time feedback, helps you find your personal resonance frequency and is especially useful for anxiety and autonomic dysregulation6.

Regular, moderate exercise also helps, provided it’s balanced with recovery, since overtraining actually lowers RSA. Meditative practices such as mindfulness and attentive relaxation raise RSA, as does good sleep. Social connection plays a notable role: in safe, connected interactions, the heart rhythms and RSA of two people become more aligned (Feldman et al., 2011; Palumbo et al., 2017): their ventral vagal systems tune to one another. A calm, well-regulated partner can in this way help the other person settle. This is called co-regulation (Porges, 2022), and it is not only emotionally valuable but also physiologically restorative.

Voice and hearing play a part too: singing, humming, and speaking melodiously activate the ventral vagus via the nucleus ambiguus, which also controls the larynx. And according to polyvagal theory, the experience of safety, so-called neuroception of safety, is a basic precondition: calm, predictable, socially supportive environments support RSA, while threat and unpredictability lower it.

In closing

Respiratory sinus arrhythmia is more than just a technical measurement. It is a window onto a deeply rooted system that supports safety, social engagement, and resilience. In mammals, the breath-linked fluctuation in heart rhythm may have lost its original function, but as a signal it remains valuable: it shows how smoothly the heart is being fine-tuned, moment to moment, via the ventral vagus.

High RSA points to a body that feels safe enough to relax and connect; low RSA points to withdrawal and self-protection. And because RSA can be influenced through breathing, movement, co-regulation, and safety, it also offers a foothold for recovery.

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Deep dive: for those who are keen to know more

This section is for readers who want to know more about the technical and scientific background underlying RSA. The general section above is likely sufficient for most readers; what follows is supplementary, not required reading.

The brainstem as conductor: the cardiopulmonary oscillator system

In short: a network in the brainstem couples breathing, heart rate, and voice, and actively generates the RSA rhythm.

In the early 1990s, Richter and Spyer described a brainstem circuit that coordinates breathing, heart rate, and laryngeal activity (Richter & Spyer, 1990). Three structures work together here. The pre-Bötzinger complex in the ventrolateral medulla (the structure located toward the front and side of the medulla oblongata, part of the brainstem) generates the basic breathing rhythm. The nucleus ambiguus regulates vagal output to the heart and larynx. The nucleus tractus solitarius (NTS) integrates sensory information, among other things from pressure receptors in the blood vessels, from oxygen and CO2 sensors, and from lung receptors, and relays it onward, including to the nucleus ambiguus and the pre-Bötzinger complex7.

These structures therefore synchronize their activity. The pre-Bötzinger complex rhythmically modulates vagal output in phase with breathing: during inhalation that output is suppressed, during exhalation it is facilitated again. The result is a centrally generated, rhythmic pattern in which breathing and heart rate are coordinated with one another. RSA is thus the output of an evolutionarily conserved system that integrates breathing, heart rate, and even vocalization.

A brief history of RSA

In short: RSA has been known since the mid-nineteenth century; Porges turned it into a usable measure in the twentieth century.

The connection between breathing and heart rate was already noted in 1733 by Stephen Hales. The first proper description of RSA is credited to Carl Ludwig, who recorded the phenomenon with his kymograph in 1847. Shortly after, Donders (1852) and Einbrodt (1860), among others, showed that breathing-induced pressure changes alone could not account for the observed fluctuations, implying that a neural reflex had to be involved. In the 1930s, Anrep and colleagues mapped the mechanism in detail (Anrep et al., 1936), and earlier still, in 1915, Eppinger and Hess linked elevated vagal tone to clinical presentations.

In the latter half of the twentieth century, Stephen Porges turned RSA into a workable measure. As a young researcher he noticed that the breathing-linked rhythm correlated with performance on reaction-time and attention tasks, and he set out to find a way to measure it cleanly (Porges, 1972). The problem was that ordinary spectral analysis ran into trouble because breathing is never perfectly regular and physiological signals are constantly changing. Together with mathematician Robert Bohrer, he developed a method that removes slow trends from the signal and then filters within the respiratory frequency band. This Porges-Bohrer method has since been used in hundreds of studies and proved sensitive enough to measure RSA in premature infants, children, and adults, even under unstable conditions.

How exactly is RSA measured?

In short: you record heart rate (and ideally breathing as well) and then isolate the breathing-linked component.

The most precise method is an electrocardiogram (ECG). The R-peak in that signal marks each heartbeat, and the time between two R-peaks forms the basis for analysis. Chest straps that record an ECG signal are suitable; optical wrist sensors are generally too imprecise for accurate RSA determination. It is useful to record breathing simultaneously, for example with a respiratory belt, because the correct frequency band varies by person and situation.

The Porges-Bohrer method works in a few steps. First, the time intervals between successive heartbeats are arranged in sequence. Then the slow, gradual changes in that signal are filtered out, leaving only the fast variation that moves with breathing. The RSA amplitude is then a measure of how large that variation is. Simpler approaches also exist, such as the difference between the fastest and slowest heart rate per breath, or isolating the breathing-linked frequency through spectral analysis. These are easier to calculate but more sensitive to disturbance. Validation studies point to the Porges-Bohrer method as the most reliable (Lewis et al., 2012).

How do we know RSA reflects the ventral vagal system?

In short: pharmacological studies, direct nerve recordings, and the timing argument all point to a vagal origin.

The vagal basis of RSA has been demonstrated in several ways. When you administer atropine, a substance that blocks cholinergic transmission from the vagus to the heart, RSA disappears completely while breathing remains unchanged. Give a beta-blocker instead, which inhibits sympathetic activity, and RSA remains largely intact. Block both at once, and what remains is a nearly flat, even heart rhythm. RSA is therefore a vagal phenomenon, not a sympathetic one.

Direct recordings from the vagus nerve further show that cells in the nucleus ambiguus fire in time with breathing, driving the fluctuation in heart rate. What you record in the nerve is the conducted signal traveling along their axons, the vagal fibers. Sympathetic neurons do not show this pattern. There is also a timing argument. RSA requires fine-tuning of the heart at every single beat, within a fraction of a second. Sympathetic transmission runs through slow cascades that take seconds to tens of seconds, far too slow. Parasympathetic transmission via acetylcholine, by contrast, works within milliseconds, because it directly opens coupled potassium channels. Only the fast, myelinated ventral vagus can deliver that speed.

Is RSA really mammal-specific?
The evolutionary debate

In short: the building blocks of RSA are not unique to mammals; what is new is how mammals integrated them.

For a long time, RSA, and the fast myelinated vagal pathway underlying it, was presented as distinctly mammalian. That claim has come under pressure from comparative physiology. Paul Grossman and Edwin Taylor (Grossman & Taylor, 2007) already raised questions about interpreting RSA as a direct, exclusive measure of the mammalian vagus, partly because RSA is strongly influenced by breathing rate and depth. Taylor, Wang, and Leite (2022) subsequently showed that the building blocks, myelinated cardiac vagal fibers, a division of brainstem nuclei, and a breathing-linked heart rhythm, were already present in sharks, lungfish, frogs, and reptiles hundreds of millions of years before mammals existed. In rattlesnakes, for instance, a breathing-linked component in heart rate has been demonstrated that closely resembles mammalian RSA (Campbell et al., 2006).

Porges has responded that breathing is not a confound but a functional part of the same system, because the coupling between breathing and heart is centrally organized in the brainstem (the shared cardiopulmonary oscillator). Filtering out breathing, on this view, does not remove noise but cuts away part of the very system one is trying to measure.

The most reconciling perspective on this debate, in my view, is that of exaptation: old components taking on a new function in a new context. The building blocks are ancient and shared, but the integration of heart, breathing, voice, and gaze into one coherent system, with the mobile, expressive face as the mammal-specific element within it, is genuinely new. If you’d like to read more on this, I recommend my article “How Old Is That Ventral Vagus, Really?” There I also work out why RSA lost its original function in mammals and became a window onto vagal regulation instead, as touched on above.

Looking ahead

In short: measurement technique, linkage to other biomarkers, and molecular research are making RSA increasingly useful.

Research into RSA continues to develop. Machine learning, for instance, is now being used to recognize patterns and make individual predictions. RSA is increasingly combined with other measures, such as skin conductance, cortisol levels, pupil size, and brain activity, to build a multidimensional picture of autonomic and emotional regulation. Wearables are becoming more sophisticated, which may eventually enable reliable measurement and just-in-time interventions. Finally, molecular and transcriptomic research may map the genetic basis of vagal specialization, including genes involved in myelination within the nucleus ambiguus.

In the area of RSA, and how we measure and interpret it, interesting developments lie ahead, ones that matter for polyvagal theory as well.

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Sources and further reading

Anrep, G. V., Pascual, W., & Rössler, R. (1936a). Respiratory variations of the heart rate: I. The reflex mechanism of the respiratory arrhythmia. Proceedings of the Royal Society of London B, 119(813), 191–217. https://doi.org/10.1098/rspb.1936.0005

Anrep, G. V., Pascual, W., & Rössler, R. (1936b). Respiratory variations of the heart rate: II. The central mechanism of the respiratory arrhythmia and the inter-relations between the central and the reflex mechanisms. Proceedings of the Royal Society of London B, 119(813), 218–230. https://doi.org/10.1098/rspb.1936.0006

Campbell, H. A., Leite, C. A. C., Wang, T., Skals, M., Abe, A. S., Egginton, S., Rantin, F. T., Bishop, C. M., & Taylor, E. W. (2006). Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake, Crotalus durissus terrificus. Journal of Experimental Biology, 209(14), 2628–2636. https://doi.org/10.1242/jeb.02278

Divon, M. Y., Yeh, S. Y., Zimmer, E. Z., Platt, L. D., Paldi, E., & Paul, R. H. (1985). Respiratory sinus arrhythmia in the human fetus. American Journal of Obstetrics and Gynecology, 151(4), 425–428.
https://doi.org/10.1016/0002-9378(85)90262-5

Escorihuela, R. M., Capdevila, L., Castro, J. R., Zaragozà, M. C., Maurel, S., Alegre, J., & Castro-Marrero, J. (2020). Reduced heart rate variability predicts fatigue severity in individuals with chronic fatigue syndrome/myalgic encephalomyelitis. Journal of Translational Medicine, 18, 4. https://doi.org/10.1186/s12967-019-02184-z

Feldman, R., Magori-Cohen, R., Galili, G., Singer, M., & Louzoun, Y. (2011). Mother and infant coordinate heart rhythms through episodes of interaction synchrony. Infant Behavior and Development, 34(4), 569–577. https://doi.org/10.1016/j.infbeh.2011.06.008

Grossman, P., & Taylor, E. W. (2007). Toward understanding respiratory sinus arrhythmia: Relations to cardiac vagal tone, evolution and biobehavioral functions. Biological Psychology, 74(2), 263–285. https://doi.org/10.1016/j.biopsycho.2005.11.014

Lehrer, P. M., Kaur, K., Sharma, A., Shah, K., Huseby, R., Bhavsar, J., Sgobba, P., & Zhang, Y. (2020). Heart rate variability biofeedback improves emotional and physical health and performance: A systematic review and meta analysis. Applied Psychophysiology and Biofeedback, 45(3), 109–129. https://doi.org/10.1007/s10484-020-09466-z

Lewis, G. F., Furman, S. A., McCool, M. F., & Porges, S. W. (2012). Statistical strategies to quantify respiratory sinus arrhythmia: Are commonly used metrics equivalent? Biological Psychology, 89(2), 349–364. https://doi.org/10.1016/j.biopsycho.2011.11.009

Meeus, M., Goubert, D., De Backer, F., Struyf, F., Hermans, L., Coppieters, I., De Wandele, I., Da Silva, H., & Calders, P. (2013). Heart rate variability in patients with fibromyalgia and patients with chronic fatigue syndrome: A systematic review. Seminars in Arthritis and Rheumatism, 43(2), 279–287.
https://doi.org/10.1016/j.semarthrit.2013.03.004

Palumbo, R. V., Marraccini, M. E., Weyandt, L. L., Wilder-Smith, O., McGee, H. A., Liu, S., & Goodwin, M. S. (2017). Interpersonal autonomic physiology: A systematic review of the literature. Personality and Social Psychology Review, 21(2), 99–141.
https://doi.org/10.1177/1088868316628405

Porges, S. W. (1972). Heart rate variability and deceleration as indexes of reaction time. Journal of Experimental Psychology, 92(1), 103–110. https://doi.org/10.1037/h0032181

Porges, S. W. (1995). Orienting in a defensive world: Mammalian modifications of our evolutionary heritage. A Polyvagal Theory. Psychophysiology, 32(4), 301–318.
https://doi.org/10.1111/j.1469-8986.1995.tb01213.x

Porges, S. W. (2007). The polyvagal perspective. Biological Psychology, 74(2), 116–143.
https://doi.org/10.1016/j.biopsycho.2006.06.009

Porges, S. W. (2022). Polyvagal Theory: A Science of Safety. Frontiers in Integrative Neuroscience, 16, 871227.
https://doi.org/10.3389/fnint.2022.871227

Porges, S. W. (2023). The vagal paradox: A polyvagal solution. Comprehensive Psychoneuroendocrinology, 16, 100200. https://doi.org/10.1016/j.cpnec.2023.100200

Reed, S. F., Ohel, G., David, R., & Porges, S. W. (1999). A neural explanation of fetal heart rate patterns: A test of the polyvagal theory. Developmental Psychobiology, 35(2), 108–118.
https://doi.org/10.1002/(SICI)1098-2302(199909)35:2%3C108::AID-DEV4%3E3.0.CO;2-N

Richter, D. W., & Spyer, K. M. (1990). Cardiorespiratory control. In A. D. Loewy & K. M. Spyer (Eds.), Central Regulation of Autonomic Functions (pp. 189–207). Oxford University Press.

Taylor, E. W., Wang, T., & Leite, C. A. C. (2022). An overview of the phylogeny of cardiorespiratory control in vertebrates with some reflections on the ‘Polyvagal Theory’. Biological Psychology, 172, 108382. https://doi.org/10.1016/j.biopsycho.2022.108382

There are two kinds of inner voice. One growls. The other whispers.

The growling voice knows no hesitation. It reacts fast, decisively, sometimes even roughly. Ignore it, and the growl swells into a roar. For it wants you to run, to strike back, or to hide. It has no use for nuance, because nuance takes time, and time is exactly what it does not have. This voice is old. Older than language or culture, older than humankind itself. We call it instinct.

The whispering voice is different in kind. It speaks not in commands but in sensations. It gives you a feeling about something, a knowing you cannot quite explain. You know the moment: you are about to make a decision that looks sensible on paper, yet something “isn’t right.” Or the reverse: something seems risky but “feels good.” That is the voice we call intuition.

Telling instinct and intuition apart can be difficult because both voices come from within, and both can feel like the “truth” of the moment. But the one truth is more about safety, the other about wisdom.

Instinct

Instinct is behavior that is already there before thinking gets a chance. It is the automatic response of a nervous system whose first priority is survival. When you startle at a loud noise, when your heart races as things grow tense, or when you withdraw during a conflict—that is instinct at work.

Seen through the lens of polyvagal theory, this involves the oldest layers of our nervous system. The sympathetic system, for instance, which mobilizes for fight or flight, or the dorsal vagus, which under severe threat brings about withdrawal and shutdown. These responses are lightning-fast, fully automatic, and bodily in essence. They were once vital to survival1, and in some situations they still can be. You recoil from the coil on the path before you know whether it’s a snake or a branch; you swerve the wheel before you have consciously seen the other car. These are remnants of a distant past that respond in a flash in the present and can save your life, long before thinking could ever intervene.

But instinct also has a flip side. It is shaped by what once happened, and it reacts from the past rather than to what is actually going on now. What is happening now resembles what happened before but is by no means always the same situation. Someone who learned as a child that a person in authority was unkind might, as an adult, react with instinctive distrust toward a manager—even toward a genuinely trustworthy boss. The instinct recognizes a pattern from the past and triggers a behavioral response. It does not do so for no reason, but it is not always the most fitting or useful reaction.

Instinct pushes you in a direction. It is urgent, bodily, and does not ask your opinion.

Intuition

Intuition is not a mystical phenomenon, even if it sometimes sounds a little like one. It arises from your nervous system’s ability to process vast amounts of information at once—information that need never reach your conscious attention—and to produce a summary of it in the form of a feeling.

Cognitive scientist Gary Klein spent decades studying decision-making in high-stress environments2. Firefighters, military officers, and chess players too. What he found surprised him: in a crisis, experts seldomly weigh their options by the book. They feel what the right choice is. Not necessarily because they are averse to procedure, but because their years of experience are stored as a capacity for pattern recognition that cannot be put into words. That is intuition through and through.

From the polyvagal perspective, intuition may be what happens when the nervous system is in a state of ventral regulation: open, present, unthreatened. From that state, the body can notice subtle signals it would likely miss in a state of alarm. Neuroception, the constant subconscious scan our nervous system performs, supplies information without pause. Intuition may be nothing more than that information finding its way into awareness—not as words or thoughts, but as feeling.

But what if that scan signals not safety but danger? Does intuition then fall silent? Not entirely: neuroception “is never switched off”; it does its work in good times and bad. What changes under threat is the register in which the information arrives. In safety there is room for nuance, and the information reaches you as a quiet, almost offhand knowing. When neuroception flips to danger, that same stream narrows into a more insistent signal that has no time to lose. In that narrowing, the past can most easily pass itself off as the present. The same body, the same subconscious scan—but now it is not the whispering voice that speaks, but the growling one.

Seen this way, neuroception feeds both voices. Intuition and instinct do not come from different sources; they draw on the same ceaseless stream of information, and the state you are in determines which of the two you hear. At the knife’s edge, when the body signals in a flash that something is off, the two merge: instinct in its speed and intuition in its accuracy, in one and the same sensation.

Intuition whispers. It asks for silence, for space, for a moment of not-knowing.

The Buddhist View

Buddhism does not draw this distinction in the same words, but it has investigated it for centuries3, and the insights this has yielded are surprisingly current.

What we call instinct, a Buddhist teacher would probably describe in terms of saṅkhāras: ingrained conditionings, traces of earlier experiences that steer behavior automatically. In the twelvefold chain of dependent origination (paṭicca-samuppāda), they are the formations that arise out of ignorance and help shape future experience. They operate below the level of conscious thought, are fed by craving or aversion, and repeat themselves until they are seen and understood.

The Mahāyāna tradition has a perhaps even more fitting term for this: vāsanā, literally the scent or residue that an earlier action leaves behind in the mind, the way a bottle of eau de toilette keeps giving off its fragrance long after it has run dry. That is what characterizes instinct. It is a scent from the past that colors the present. The meditator learns to notice these traces—not to suppress them, but to no longer be swept along by them unawares.

Intuition has a related concept in Buddhism: prajñā, usually translated as “wisdom,” “insight,” or “understanding.” But a nuance is in order here, because prajñā is not, in origin, the proverbial gut feeling. It is insight into the nature of reality itself: into impermanence, into suffering, into the absence of a fixed self.

What instinct and intuition share is the quality of direct seeing without the intervention of reasoning. In the Zen tradition, that moment is sometimes described as the instant in which thinking falls still and reality is perceived clearly. Monks train at this for years—not by thinking harder, but by letting the conditionings settle so that room opens up for a quality of being no longer dictated by fear or desire.

Buddhism adds a warning worth taking seriously. What we call intuition is by no means always prajñā, or wisdom. It may just as easily be a vāsanā in disguise: a fear posing as wisdom, a wish that sounds like inner knowing. The Zen tradition even has its own word for this: makyō, the illusory images and convincing sensations that arise during sitting and that the practitioner all too easily mistakes for genuine insight. The instruction to the practitioner is always the same: do not cling to it, however pleasant or “true” it may feel. For the conviction that something is true is not itself proof that it is.

This is why meditation practice places such emphasis on non-attachment—including to your own insights. The oldest writings of the Buddhist canon even warn against clinging to views (diṭṭhi), because the very certainty with which we hold something to be true can blind us. A teacher might therefore say: As long as you have not trained sufficiently in stillness and non-reacting, what you call intuition is in large part conditioned instinct in disguise. Only when the traces of the past come to rest does something begin to speak that is truly freer.

The Difference?

An understandable question… The honest answer is that you do not always see the difference—not for certain, and not right away—but there are clues.

Instinct feels urgent. It wants now. It is physically tense, sometimes oppressive, sometimes even aggressive. It tolerates no delay. Instinct does not ask for reflection; it demands action.

Intuition feels different. It is calmer in tone, even when it says something important. It can wait. It does not vanish after a night’s sleep. It is still there when you ask after it the next morning. Intuition is no less bodily than instinct, but it has a different quality. More a quiet certainty than an alarm.

A practical question that can help: from what state am I perceiving this? If you are stressed, poorly rested, feeling threatened, or still simmering from a conflict, the odds are good that what presents itself as intuition is actually instinct. Your nervous system is on high alert and colors the world from threat, not from wisdom.

When you are grounded, present, and sufficiently at ease, what you perceive arrives more cleanly, undistorted by alarm.

Practicing the Distinction

Silence is a great help because instinct often fades once the acuteness falls away, whereas intuition remains. Give yourself room to let a feeling settle. Ask yourself: is this based on what is here now, or on what was there before?

Body awareness helps too. Instinct typically shows up as muscular tension, a clenched stomach, or a fleeting urge. Intuition more typically feels like a calm, sometimes almost offhand, sensation. Not spectacular, but present nonetheless.

And openness helps most of all. The willingness to ask: do I want this, or do I know this? Do I wish this were true, or do I feel that it is? These are subtle questions, and they can make a great difference.

In Closing

Instinct has perhaps saved you many times already. And intuition has regularly shown you something that thinking alone would never have found. The point is not which voice to trust and which to distrust. The point is that you come to know them, recognize them, and tell them apart—for instinct watches over your safety, and intuition reaches toward wisdom. Precisely now, when we make so many decisions under pressure, the ability to keep the two apart grows ever more precious.

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Welcome to my longest article on RelaxMore.net so far. It cost me a fair amount of work, but it was worth it. Working through the scientific sources was intensive, instructive, and enjoyable. But most of the work went into finding the wording that does justice to both sides of a debate that has been running for almost thirty years and that I am now writing about. Take your time to read it. Because it is a long piece, I will begin with a summary. I also hope it will leave you all the more curious about how the story unfolds.

Summary

Since the mid-1990s, there has been debate about the evolutionary foundation of polyvagal theory. On one side stands Stephen Porges, who presents the ventral vagal system (= the social engagement system) as typically mammalian: a new, fast vagal brake on the heart, originating in the nucleus ambiguus, that enables mammals to seek social contact and to calm one another. On the other side stands a group of comparative physiologists led by Edwin Taylor, who have shown that the building blocks Porges names—myelinated cardiac vagal fibers, two nuclei in the brainstem, and a respiratory-modulated heart rhythm (I explain all the terms further on)—already existed hundreds of millions of years before mammals, in sharks, lungfishes, frogs, and reptiles.

At first glance this looks like a discussion that has to produce a winner. But the opposition turns out to be far less spectacular once you apply the evolutionary concept of exaptation: the phenomenon whereby an existing structure acquires a new function in a new context. The building blocks are therefore old, but what mammals have done with them is indeed new: an integration of heart, breathing, and voice into one coherent regulatory system, organized around something no other vertebrate possesses to this degree, a mobile and expressive face.

In this article I show how that perspective unites Porges and his critics within a single evolutionary framework and how it makes polyvagal theory, paradoxically, more empirically testable than it was in its original form.

A thirty-year disagreement

Since the mid-1990s, there has been debate about the evolutionary foundation of polyvagal theory (Porges, 1995, 2011). On one side stands Stephen Porges, the American scientist who developed the theory. He argues that mammals, and therefore we humans too, possess a special neural pathway that other animals do not have.

This neural pathway1 is part of the tenth cranial nerve, the well-known vagus nerve. According to Porges, this pathway makes it possible for mammals to find rest in one another’s company and to convey safety to one another through their body language, voice, and facial expression. It is the neural, bodily, and behavioral foundation of what he calls the social engagement system.

On the other side stands a group of comparative physiologists, researchers who compare the nervous systems of different animal groups with one another. The British emeritus professor Edwin Taylor (University of Birmingham), together with Tobias Wang (Aarhus University) and Cleo Leite (Federal University of São Carlos), has for decades carried out research into the regulation of heartbeat and breathing and the coordination thereof in fishes, frogs, lizards, and birds2. In 2022 they published an article titled “An overview of the phylogeny of cardiorespiratory control in vertebrates with some reflections on the ‘Polyvagal Theory’” (phylogeny being the study of the evolutionary descent of a group of organisms, and cardiorespiratory control the regulation of heartbeat and breathing).

An overview of the phylogeny of cardiorespiratory control in vertebrates with some reflections on the ‘Polyvagal Theory

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Their objection to polyvagal theory is not that Porges’s functional account of social behavior is nonsense. Their objection runs deeper: they say that the building blocks on which Porges bases the system—contrary to what he claims—do not occur exclusively in mammals at all. Those nerve fibers, those brainstem nuclei, that interplay between breathing and heartbeat: you already find these in fishes, lizards, and frogs as well. Taylor, Wang, and Leite describe this position at length in their, incidentally very interesting, article (Taylor, Wang, & Leite, 2022; see above for a PDF). Earlier, Paul Grossman had already advanced a methodological critique pointing in a similar direction (Grossman & Taylor, 2007; Grossman, 2023).

At first glance this looks like a fight that can have only one winner. Either the building blocks are typical of mammals, or they are not. But anyone who conducts the debate in this either-or fashion misses something important. There is a third possibility that does justice to both sides, a both-and model. The room for it lies hidden in an evolutionary concept called exaptation, a word I explain further on. With the help of that concept, the opposition turns out to be less irreconcilable than it seems.

We begin with the basics

Before we dive into the debate itself, I will first explain a few concepts so you can follow the reasoning.

The vagus nerve

The vagus nerve is the tenth cranial nerve. It is a long, fairly thick nerve that runs down from the brainstem and branches out to the heart, the lungs, the larynx, and the organs in the abdomen. It is the longest nerve in the body. The vagus belongs to the parasympathetic nervous system: the part of our nervous system that is active in rest and recovery, that slows the heartbeat, supports digestion, and is involved in voice and facial expression, but also in shutdown and collapse responses under stress that we experience as life-threatening.

The vagus does not have one origin in the brainstem, but two. In the brainstem there is a cluster of nerve cells situated more towards the back: the dorsal (= back side) motor nucleus of the vagus, abbreviated DMNX. And there is a cluster of cells situated more towards the belly side (= ventral): the nucleus ambiguus, abbreviated NAmb. That these are two different brainstem nuclei is important in polyvagal theory. Porges links them to different functions. The DMNX is, in his view, evolutionarily old and is associated with collapsing, shutting down, and dissociation under overwhelming threat, which in polyvagal theory is called shutdown or collapse. The NAmb, by contrast, is said to have a function in mammals that no other animal group possesses. Not so much because this nucleus would be absent elsewhere (Porges himself acknowledges that an NAmb-like structure is already present in reptiles), but because the fast, myelinated fibers (the next concept I will explain) that run from the NAmb to the heart, and the way they are connected to face, voice, and hearing, are, in his view, unique to mammals. This NAmb branch is said to make it possible to seek social contact, to calm down, and to be in connection.

A word of warning is in order here, because I just used the word “branch,” and that word is actually misleading. You encounter it everywhere in the literature on polyvagal theory: the ventral vagal branch, and the dorsal vagal branch, as if these were two separate cables each finding its own way through the body. That is not how it works. The fibers that come from the DMNX and the fibers that come from the NAmb do not run separately but become interwoven into the same nerve strand even before leaving the brainstem. So do not picture two loose wires, but one rope in which threads of different origin are braided together. The cardiac branch of the vagus, which runs to the heart, therefore contains fibers from both nuclei, fast myelinated and slow unmyelinated, mixed together (Taylor et al., 2022). Incidentally, I will keep speaking of “branches” in this article because it is a handy and well-established word, but you now know it is a simplification.

That the two types of fibers can be distinguished functionally therefore does not mean that they are anatomically separate. The distinction lies in their origin and in their behavior, not in two loose branches. This may seem a detail, but it touches on something that recurs throughout this article: a functional distinction is something other than a physical separation. Anyone who imagines the ventral and the dorsal vagus as two separate neural pathways makes exactly the thinking error that also underlies part of the criticism of polyvagal theory. I will return to this further on.

Myelin

One more concept is important: myelin. Some nerve fibers are wrapped in an insulating layer of fat and protein. That layer, myelin, allows signals to travel much faster through the fibers. Compare it with the plastic insulation around an electrical wire. Nerve fibers with myelin conduct up to ten times faster than fibers without myelin. An important claim of Porges about the control of the heart is that only mammals have myelinated NAmb fibers for this purpose, and that these fast fibers form the basis for the delicate interplay between breathing and heartbeat that expresses itself in heart rate variability.

That interplay itself is called respiratory sinus arrhythmia, abbreviated RSA. It is the natural phenomenon whereby the heart speeds up a little on inhalation and slows down a little on exhalation. It is often considered a sign of a healthy, flexible nervous system.

What Taylor and colleagues have shown

With these concepts in hand, we can look at what Taylor, Wang, and Leite published in 2022 in the journal Biological Psychology (Taylor et al., 2022). Their review article condenses decades of research into a structured critique of the evolutionary underpinning of polyvagal theory. Their argument has four main lines.

The first line concerns the inhibition of the heart at rest. In all vertebrate animals studied, from sharks to mammals, the heartbeat at rest turns out to be slowed by the vagus. In reptiles this brake even turns out to be very strong. In the rattlesnake the heart rate roughly doubles when the vagal influence is removed with atropine (Campbell et al., 2006), whereas in humans the increase usually stays between thirty and fifty percent. A slow metabolism, therefore, goes perfectly well together with a powerful vagal grip on the heart. That takes some getting used to for the intuition, which expects a cold-blooded, slow animal to have a loose rather than a tight rein. Strong vagal control of the heart at rest is, in any case, no mammalian novelty. Whether that control in reptiles also rests on the same fast, myelinated fibers as in us is a separate question, to which I return at the third line.

The second line concerns the two origins of the vagus in the brainstem. Porges presents it as a typically mammalian feature that vagus fibers controlling the heart arise from two nuclei in the brainstem: in the DMNX and in the NAmb. But Taylor and his colleagues show that this division already exists in the dogfish. In this shark the greater part of the vagal nerve cells lies in the DMNX, but there is also a cluster situated more towards the front (= ventral), and in that cluster there already lie cells that control the heart. Taylor and colleagues see this ventrolateral group as a possible precursor of what in mammals has become the nucleus ambiguus. In crocodiles, lizards, snakes, and frogs, the authors find comparable distributions. In the African clawed frog, as much as 30% of the relevant vagal nerve cells already lie in that front brainstem nucleus. The division is not only old; in the ventral group of the shark there already lie cardiac vagal neurons, at a location that Taylor regards as a possible precursor of the mammalian NAmb. And its relative size increases through evolution, from ten percent in the shark to thirty in the clawed frog and an extensive nucleus in us. So not an invention of “ours,” but an expansion.

The third line concerns the myelinated fibers. Porges’s claim here is specific: not that myelin would be present somewhere in the vagus, but that only mammals possess fast, myelinated cardiac fibers that can fine-tune the heart from moment to moment within a respiratory-modulated (= driven by breathing) circuit. Literally: “Only mammals have a myelinated vagus” (Porges, 2009, 2011). With the electron microscope, Taylor and colleagues have meanwhile demonstrated these fibers in the cardiac vagal branch in sharks, lungfishes, rattlesnakes, lizards, and toads as well. In the dogfish and the South American lungfish, the conduction velocities, moreover, turn out to match those of certain fibers in mammals. And in both the lungfish and the rattlesnake, these fibers take part in a respiratory-modulated heart rhythm that resembles the RSA we know in mammals. So this is not a matter of a few exceptions where myelin has been found “somewhere,” but of the same functional package that Porges presents as mammalian.

The fourth and theoretically most interesting line concerns the interplay between breathing and heartbeat itself. Taylor and his colleagues call this cardiorespiratory synchronization (CRS): each heartbeat coincides with a breathing movement, a one-to-one coupling, controlled from the DMNX3, which optimizes the counter-flow of blood and water across the gills for maximum oxygen uptake. In air-breathers, such as lungfishes, frogs, reptiles, birds, and mammals, the coupling between breathing and heartbeat looks fundamentally different. The heartbeat is then much faster than the breathing rhythm, so a strict one-to-one coupling is no longer possible. Instead, breathing influences the speed of the heartbeat: during inhalation the vagal brake on the heart is briefly released so that the heartbeat accelerates, and during exhalation the brake is applied again. This pattern, in which the heart rate fluctuates to the rhythm of breathing, is what in mammals we call respiratory sinus arrhythmia (RSA). This same mechanism has thus been found in lungfishes and cururu toads, animals whose lineage split off hundreds of millions of years ago from the line that would eventually lead to mammals4.

The most surprising insight lies in the authors’ concluding thought. In reptiles and amphibians, which have a heart in which the pulmonary and systemic circulations are not fully separated—as is the case in us—this fluctuation in heart rate with each breath helps to send blood efficiently to the lungs5. Mammals no longer need that efficiency gain: our heart has fully separated atria and ventricles for the pulmonary circulation and for the systemic circulation. RSA in mammals is therefore actually not an evolutionary innovation. It is a remnant from a time when the rhythm still had real work to do and still beats today 😉, but without the clear physiological role it still fulfills in animals with cardiac shunting.

Here a question may arise. If RSA in mammals has lost its original function, why then does heart rate variability (of which RSA is an important component) count as a measure of health? The answer is that RSA in us is valuable not for what it does, but for what it reveals. The fluctuation of the heartbeat with the rhythm of breathing arises because the fast ventral vagal fibers continually fine-tune the heart. The magnitude of that fluctuation is thereby a window onto how smoothly that vagal regulation works. A lot of variability points to a flexible, responsive system; little variability to a system that falters through stress, illness, or age. RSA in mammals is therefore no longer a functional mechanism but a usable and measurable signal, and in that capacity it is valuable.

What Taylor explicitly does not claim

In the article by Taylor and colleagues, there are a few remarks that often remain underexposed. In their introduction and in their conclusion, the authors say explicitly that they do not wish to say anything about the role of the vagus in human social behavior. They literally write that they do not claim to be able to “say anything useful about the possible roles of a social engagement system in humans that might in some way involve parasympathetic input via the vagus nerve” (Taylor et al., 2022). At the same time, they leave no doubt that they regard the “smart vagus” concept itself, with which Porges grounds that social engagement system, as superfluous. Their delimitation therefore concerns only the psychological and clinical elaboration of the theory; about the neurobiological building blocks beneath it, they do speak out. They acknowledge that the vagus fulfills many important functions in us. Their criticism is confined to what they have themselves studied: the comparative physiology of the heart and breathing in different animal groups.

This is an essential delimitation of their field of research and scientifically very sound. What Taylor and his colleagues refute is the claim that the anatomical building blocks are typical of mammals. What they therefore do not contradict is the claim that mammals have an integrated system in which face, voice, and heart work together to make social contact possible. Here it already becomes apparent that polyvagal theory and the criticism of Taylor and his colleagues need not exclude one another.

Lungfish?

At this point, as a level-headed reader, you may wonder, what does a lungfish have to do with me? My ventral vagus regulates how I deal with colleagues, my capacity to calm my child, and my voice in a conversation. A lungfish does not flirt, does not smile, and does not comfort a partner. What is it doing here in the story, then?

The answer lies in a distinction that matters in evolutionary biology. When a trait occurs in different lineages, it can have arisen in two fundamentally different ways. It can have been invented independently, each time anew, in each lineage separately. That is called convergent evolution: bats, birds, and pterosaurs all three have wings, but each along its own evolutionary path. The common ancestor had no wings. Or it can have been inherited from a common ancestor that already possessed the trait, after which all lineages retained it. That is called homology.

As you can see above, the difference between convergent and homologous seems easy to delineate, but in practice the two do sometimes blur into each other. Take the eye. A light-sensitive organ is estimated to have arisen independently dozens of times in the animal kingdom, from the compound eye of insects to the camera eye of vertebrates and squids. At the level of construction, the eye is therefore a textbook example of convergence: invented again and again, with different parts and different optics. And yet there is a surprise underneath. All those independently arisen eyes turn out to be switched on by the same genetic switching mechanism: the so-called Pax6 gene plays a key role in the formation of eyes in virtually all animals. That gene is homologous, inherited from a distant common ancestor6.

The eye is therefore at once convergent and homologous: convergent in its construction, homologous in its genetic control. The ancient gene gave, in different animals, the starting signal “build an eye here,” and each lineage filled in that command with its own means. Precisely this difference between levels is what we need to understand the vagal story. Because there, too, it holds: you must know at which level you are looking before you can say whether something is old or new.

Taylor and his colleagues take a very clear position: the mechanism of the vagal brake on the heart, with myelinated fibers and respiratory modulation, is homologous. It was not invented independently by lungfishes, toads, and mammals but inherited from a common ancestor that lived somewhere in the Devonian, about four hundred million years ago. That ancestor already had the mechanism: the fast fibers, the cells that control the heart, and the coupling with the breathing rhythm. And all its descendants, each via its own evolutionary trajectory, received it and passed it on in slightly modified form.

This is a more important point than you might say at first glance. If the trait had arisen convergently, Porges could still maintain that mammals developed it anew, as a unique invention on their own evolutionary path. But homology means that it is ancient heritage. The anatomical building blocks, a ventral group of cardiac vagal neurons with myelinated fibers to the heart, are not typically mammalian. They are already present in recognizable form in the dogfish and recur in virtually all later vertebrates. And the RSA-like coupling of heart rhythm and breathing that mammals show, they share with lungfishes, frogs, reptiles, and birds. The mechanism is therefore not new in mammals; it is ancient.

And here, then, it does indeed touch the human being. Not because we have anything to do with the lungfish in our daily life, but because it undermines the timeline of Porges’s theory. Porges bases his theory on the claim that mammals developed a new building block that makes the social engagement system possible. If that building block was already present in the lungfish, that account is no longer tenable in its original form.
It then becomes time to reconsider what mammals really do that is new.

And that is precisely what I am working towards with this whole article: not the building blocks, but what mammals have done with them, is new. The lungfish therefore belongs in this story as a witness to an ancient inheritance that we share with it. The question then becomes: how can we understand what mammals have done with that inheritance?
Here an evolutionary concept comes into play that is called exaptation.

Exaptation

In 1982 the American evolutionary biologist Stephen Jay Gould and his colleague Elisabeth Vrba published a short but influential article under the title “Exaptation, a missing term in the science of form” (Gould & Vrba, 1982). Their thesis was that evolutionary biology had, until then, been missing an important category of form and function.

Until then, one spoke mainly of adaptations: traits that arose through natural selection for the sake of the function they fulfill. The long legs of a horse are an adaptation for running fast; the webbed feet of a duck are an adaptation for swimming. But Gould and Vrba pointed out that many traits that now fulfill a particular function did not arise for the sake of that function. They were shaped in a different environment, for a different purpose, and only later came to fulfill a new function.
For this type of form and function, they coined the term exaptation7.

The term “exaptation” is formed by analogy with “adaptation.” Where the prefix ad- (= towards) points to a trait that has been shaped towards a purpose, ex- (= out of) points to a trait that comes from somewhere else and only later turned out to be useful.

A few examples are probably clarifying: bird feathers almost certainly did not arise for flight. They arose in feathered dinosaurs, presumably for heat insulation or for the sake of sexual display. Only much later, when some species climbed into the treetops and began to make gliding flights from there, did these feathers acquire a repurposing for flight. The middle-ear bones of mammals (the hammer, the anvil, and the stirrup that pass sound on to the inner ear) once arose as bones in the jaw of early precursors of mammals. When the jaw construction changed, those bones lost their old function and were repurposed in hearing. Lungs probably evolved from gas-exchange organs in early fishes that lived in oxygen-poor water; only later were they used for breathing on dry land.

Purposeless, yet reconstructable

The core of exaptation is simple: a trait is older than the function it now fulfills8; it was already there before it became useful. With an adaptation, by contrast, the trait spread precisely because it was useful: ducks with better webbed feet turned out to have greater chances of survival, so webbed feet became more common over the course of many generations. With an exaptation, the trait already existed for another reason, or without any particular reason, and only later turned out to be useful for what it now does. Think again of the feathers of birds, which arose in dinosaurs that could not fly and only much later turned out to be usable for an entirely new function: flying. The feather, then, was there before flight.

With neither adaptation nor exaptation, there is any plan or intention; evolution, after all, strives towards nothing. The distinction is therefore not about goal-directed versus purposeless, but about the question: was a trait already useful while it was arising, or did it exist before it became useful? And how do you establish that if no one was there to witness the origin?

The answer is that you reconstruct it from evidence. Three kinds of clues help here. The first is the order in time: if a trait already existed in ancestors before it acquired its current function, then it is older than that function. Think again here of the feathers in feathered dinosaurs that could not fly. They prove that feathers were there before flight, and feathers are therefore an exaptation. The second clue is the form itself: a trait that developed together with its function is usually well attuned to it, whereas a repurposed trait often bears traces of its old function9, or one whose old function even remains a riddle. The third clue is the comparison between species: by looking at which relatives do and do not have the trait, you can reconstruct when and in what form it originally arose.

The distinction between adaptation and exaptation is therefore not a matter of guessing at intentions but an empirical10 question to be answered via fossils, family trees, and comparative research. And it is precisely this that also makes it testable.

And then there is “integration”

One concept is still indispensable here because it highlights a side that must not be missed in the whole discussion: integration. This is a functional term that points to the phenomenon whereby separate parts together do something they cannot do separately11. Heart, breathing, voice, face, hearing, and social orientation have each been studied separately by different disciplines. But in mammals they work as one coherent regulatory system. This difference in level of analysis is precisely what makes Porges and the comparative physiologists talk past one another.

Taylor and his colleagues study separate parts: nerve fibers, brainstem nuclei, conduction velocities. Porges looks at what those parts produce together. Both approaches are important and legitimate; they simply operate at different levels, and when they enter into debate with one another as if it concerned the same level, misunderstandings easily arise.

One of those misunderstandings I announced earlier, with the word “branch.” Anyone who imagines the ventral and the dorsal vagus as two separate neural pathways wrongly translates a functional distinction into a physical separation. And precisely such a confusion of levels, one moment talking about separate fibers, the next about a coherent system, feeds part of the opposition between Porges and his critics. Much of what is presented as incompatible turns out, on closer inspection, to be a matter of talking at different levels.

Porges’s own reformulation: a half step towards exaptation

An interesting development in this debate is that Porges himself, since about 2021, has in his formulations come very close to the exaptation idea. Without using the term, he does move conceptually in that direction.

In his 2021 article in the journal Comprehensive Psychoneuroendocrinology, Porges no longer speaks of a “unique mammalian system” but of a “repurposed” system (Porges, 2021). Strictly speaking, an intention still resonates in that word, as if something is deliberately given a new task, whereas we know that exaptation takes place without a plan. But apart from that nuance, the move Porges makes is remarkably close to the exaptation idea.

Examples of his formulations: “The nervous system was repurposed to suppress defense strategies in favor of social behavior.” Elsewhere he writes that evolution is said to have repurposed the mammalian vagal complex to facilitate social behavior. In his 2022 article in Frontiers in Integrative Neuroscience, he says it even more explicitly: “Evolution is a process of modification in which existing structures and circuits are adapted to fulfill adaptive functions.” (Porges, 2022). That last is almost word for word what Gould and Vrba meant in 1982 with exaptation. With it, Porges in fact acknowledges that the building-block level is untenable and shifts to the synthesis level. But he does not label this as a correction of his earlier claims.

A second shift concerns the anatomical reference point. In his original work from the 1990s, Porges spoke of the NAmb, the brainstem nucleus that lies somewhat more towards the front (that is, ventral) and from which the faster vagal fibers arise, as the source of what he called the “smart vagus” (Porges, 1995, 2011). In his work from 2021 onwards, he speaks consistently of the ventral vagal complex, a larger group of nerve cells that includes not only the NAmb but also the brainstem nuclei that control the facial muscles, the jaw muscles, and the little muscles in the middle ear (Porges, 2021, 2023).

What is specifically mammalian, therefore, lies not in one separate brain nucleus, nor in a larger collection of nuclei as such. It lies in something that makes mammals unique among the vertebrates: a mobile, expressive face, and in the way old vagus building blocks have come to work together with it. Most mammals have real facial musculature, the muscles under the skin with which we smile, frown, and let our gaze speak. Fishes, reptiles, and birds lack these entirely; a lizard cannot frown, a bird cannot contort its face12. That new face calls for control, and it is that control that in mammals became interwoven with the old regulation of the heart.

At the same time, Porges leaves standing other statements that this half step has not resolved. He continues to write about “the transition from asocial reptiles to social mammals” (Porges, 2021). That is not entirely correct empirically. Researchers such as Doody, Burghardt, and Dinets devoted a whole book in 2021 to the social life of reptiles, with parental care, group formation, and collective nest protection (Doody, Dinets, & Burghardt, 2021). In 2023 they published an article in Biological Psychology in which they directly refute the assumption that reptiles are asocial (Doody, Burghardt, & Dinets, 2023). The exaptation formulation I propose here resolves this tension: it lets social behavior in reptiles stand in its own right, without thereby denying the specifically mammalian interplay of face, voice, and heart.

A final issue concerns the scientific status of the theory itself. In 2021 Porges wrote, “The theory was not intended to be proven or refuted, but to be informed by research and modified.” (Porges, 2021). That is, in terms of the philosophy of science, a problematic statement, one that critics have also regularly held against Porges. A theory that withdraws from testing (which, incidentally, is not what Porges said nor meant) places itself outside science13. Here the exaptation form of polyvagal theory offers an unexpected way out. It actually makes the theory more testable rather than less. The central claim shifts towards the presence and operation of a coherent face-voice-heart system in mammals, and away from anatomical statements that comparative physiology has by now refuted. What remains is open to empirical investigation14.

Polyvagal theory as a theory of exaptation

When we lay the Taylor article and polyvagal theory side by side and view them through the lens of exaptation, the apparent opposition dissolves into a workable synthesis.

It is clarifying here to see that exaptation works on three levels at once and that it is meaningful to keep those levels apart.

At the evolutionary level, exaptation is a form-and-function interpretation: old building blocks acquire a new role in a new environment. At the neurobiological level we see a reorganization: existing networks that become coupled differently acquire a different hierarchy and come to communicate with one another in new ways. At the functional level we see the integration of heart, breathing, voice, face, and hearing that come to operate as one coherent system.

These three levels do not describe three different phenomena, but one phenomenon from three perspectives. Anyone who looks only at the level of the separate building blocks (as sometimes happens in the discussion) sees the continuity with other vertebrates and concludes that nothing special is going on in mammals. Anyone who looks only at the functional level sees the special character but misses the evolutionary continuity. Only when the three levels remain in view at the same time does the story fall into place.

The building blocks that Porges initially presented as typically mammalian (myelinated vagus fibers, a ventral group of heart-controlling vagus cells, a breathing rhythm that modulates the heartbeat) are, empirically speaking, not inventions of mammals. They form part of a much older equipment that all vertebrates share. But what is indeed new in mammals is the way these old building blocks have been integrated into a coherent ensemble that exists nowhere else in the animal kingdom in this form.

In mammals

What is really new in mammals is therefore not the separate building blocks, but the combination. And this combination shows itself most clearly in something no other vertebrate animal possesses: a mobile, expressive face. That face itself is indeed a new anatomical acquisition; what is called exaptation lies not in that face as such, but in the way old vagus building blocks have come to work together with it.

Mammals are the only animal group with real facial musculature, the muscles under the skin with which we smile, frown, blink, and let our gaze speak. These muscles in mammals are diverse and differentiated and are connected with the movements of lips, jaw, tongue, and larynx. Fishes, reptiles, and birds lack this entirely: a lizard cannot frown, and a bird cannot contort its face. On top of that, the larynx develops into a refined apparatus for voice and intonation, and the middle ear acquires a control system that can dampen or amplify sound frequencies, attuned to the sounds that conspecifics make. In babies, several cranial nerves coordinate sucking, swallowing, and breathing together, a pattern that exists in this form in no reptile or amphibian.

That all of this became possible in mammals is connected with a second characteristic: warm-bloodedness. This is, incidentally, not unique to mammals. Birds are also warm-blooded, and there are strong indications that the common ancestors of mammals, birds, and crocodilians possessed a form of warm-bloodedness (Grigg et al., 2021). A warm-blooded animal maintains its body temperature. It can thereby permit itself something a cold-blooded animal cannot, namely a continuous, delicate fine-tuning of the physiological state, partly dependent on what is happening socially. That permanent fine-tuning costs energy, and it is precisely that energy that a warm-blooded animal has available. Warm-bloodedness is thereby not itself the innovation, but a precondition that makes the innovation possible.

And here it becomes visible what the exaptation precisely is. Not the facial expression itself, for that is a new acquisition. And not the vagal brake on the heart; that is, in fact, ancient, and we share it with lungfishes and reptiles. The exaptation is the connection between those two: an old mechanism, the fast vagal brake that can fine-tune the heart from moment to moment, that comes into the service of something utterly new, namely a face that can show an inner state and read it in another. The old heart regulation acquired a social role that became possible only once there was an expressive face to communicate with and once there was enough energy to let that attunement take place continually. This is exaptation in its clearest form: an old part that, in a new configuration, acquires a new meaning.

And in fact that repurposing reaches further than this single coupling of heart and face. For the social engagement system is built up out of a whole series of old parts. The middle-ear bones with which we make out another’s voice arose, as we saw earlier, as fragments of the jawbones of reptiles and sharks and only later acquired their role in hearing. The larynx, with which we shape vocal timbre and intonation, goes back to a valve that closes off the lower airway, a function it still fulfills; the formation of voice came only later. And the vagal brake on the heart is hundreds of millions of years old. Some of these parts, moreover, were already connected with one another earlier. In diving reptiles, the larynx and heartbeat work together to save oxygen during a dive. The separate pieces, and even some of their connections, are therefore not an invention of mammals.

What distinguishes mammals is something else. Around one truly new acquisition, the mobile face, this old assemblage came into the service of a new function: not the saving of oxygen or the protection of the airway, but the showing, sounding, and reading of an inner state between conspecifics. The social engagement system is thereby not merely an example of exaptation. It is a whole ensemble of old parts and old connections, repurposed, expanded with a new element, and as a whole put into the service of something none of the parts could ever do separately: social connection.

How tightly this whole is neurally integrated, in the sense Porges has in mind, is a question that requires further research; about this the comparative physiology of Taylor and his colleagues makes no pronouncement. But that mammals possess a communication channel no other animal has and that this channel has carried the old heart regulation along into a new, social function is beyond doubt.

And it is precisely that communication channel that touches on what forms the heart 😉 of polyvagal theory: the concept of safety. For where this economical, delicate regulatory system really makes a difference is in the proximity of conspecifics. An animal that can choose only between sympathetic defense, fight or flight, or dorsal shutdown soon experiences the proximity of another as a threat. But an animal that can subtly fine-tune its heart rate and its facial expression via the ventral vagus can be near another without going on the defensive. It can tolerate proximity and even seek it out. That is physiologically important because it means that the proximity of a conspecific need not immediately turn into a fight-or-flight reaction. And there we also find the precondition for everything that subsequently became socially possible: not fighting but attuning, not fleeing but connecting, not merely surviving but surviving together. The ventral vagus did not bring about that cooperation on its own, because cooperation, which ultimately led to civilization, has many roots: from a prolonged childhood in which several adults care for one child, via shared language and intentionality, to the cultural capacity to pass on knowledge to following generations. But the ventral vagus did provide the bodily foundation on which a sense of safety in one another’s proximity could arise, and without that foundation the rest would not have been possible. An outdated mechanism, once at work in the regulation of the heart, thus became the silent precondition for a life among and with conspecifics.

What this means for theory and practice

This reformulation has consequences that are worth making explicit.

For polyvagal theory itself, the exaptation perspective means that the evolutionary claims as Porges originally formulated them can no longer serve as necessary underpinning. The statement that only mammals would have a myelinated vagus, or that the dorsal motor nucleus is evolutionarily older than the nucleus ambiguus, does not hold up against what current comparative physiology shows. Those statements therefore need no longer be part of the theoretical edifice. What remains, and what is well defensible empirically and clinically, is the claim that mammals, and specifically humans, have a coherent face-voice-heart system that couples social behavior and bodily regulation in a way that has no equivalent elsewhere in the animal kingdom. This claim does not stand or fall with the question of whether the nucleus ambiguus already occurs in lizards.

For clinical practice, this is a reassuring outcome. The usefulness of polyvagal-informed approaches (social contact as a regulator of physiological state, vagal tone as a marker of flexibility, co-regulation as a treatment element) is largely independent of the question of whether the critics or Porges are right about sharks and lungfishes. The observations that carry the clinical theory are observations of humans under social and more stressful circumstances. These remain valid as long as they are empirically confirmed in their own right.

And yet the distant past and the consulting room touch one another. What took shape over hundreds of millions of years, namely that proximity becomes possible only when the body feels safe enough to let down its defenses, is precisely what plays out on a small scale in every treatment room. Co-regulation works not in the first place through a technique, but because the other’s nervous system learns to register proximity as safe again. The therapist does, perhaps even in a single encounter, what the ventral vagus made possible over the course of evolution.

For the scientific discussion, finally, the exaptation perspective means that the war of words may come to rest. Taylor and his colleagues end their article with a remark that may be considered an invitation to Porges: a theory deserves regular testing, and they are curious how polyvagal theory will develop under that testing.

The question is not who has the right on their side. The question is whether polyvagal theory is willing to adjust its vocabulary in such a way that the building-block claim is detached from the coherence claim and thereby acquires an evolutionarily more precise and clinically stronger formulation.

How old?

So what is the answer to the question this article began with: how old is the ventral vagus, really?

That depends on what you mean by it. The anatomical building blocks, ventrolaterally located cardiac vagal neurons with myelinated fibers to the heart, are at least five hundred million years old and go back to the common ancestor of all vertebrates. The respiratory-modulated version of it, the pattern in which the heart rhythm fluctuates to the rhythm of breathing, is about four hundred million years old and is connected with the origin of lung breathing. The specific integration of heart, breathing, voice, and face into one coherent regulatory system around a mobile and expressive face is about two hundred million years old and coincides with the origin of mammals.

The ventral vagus is therefore at once ancient and very “young.” Which answer is correct depends on the level at which you look. And that is where the exaptation perspective shows its value.

In conclusion

The comparative physiology of Taylor, Wang and Leite is not an attack on polyvagal theory as a therapeutic framework. It is a correction of a specific evolutionary claim in a field where these three researchers are among the greatest authorities in the world. Anyone who reads their work as a rejection of PVT misses an opportunity for clarification. Anyone who reads it as building material for a more mature formulation of polyvagal theory, a formulation that distinguishes its building blocks from its coherence and explains that coherence as exaptation rather than as anatomical invention, holds in their hands a framework of thought that supports clinical practice better than the original version did.

A delimitation is in order here. The criticism discussed in this article is the evolutionary criticism: the question of whether the building blocks of the system are really specifically mammalian. That is not the only criticism polyvagal theory has received. There are also methodological questions, for example, about how ventral vagal activity can best be measured, and there is discussion about the clinical claims. These fall outside the scope of this article. What I have wanted to show here is that precisely the evolutionary objections, which at first glance seem to hit hardest, lose their sharpness as soon as you view them through the lens of exaptation. The building blocks are old; that point Taylor and colleagues score. What mammals do with them is new; that point remains for Porges. And exaptation is the key point at which those two truths come together.

A brief methodological remark to finish. Earlier in this article I noted that heart, voice, and face in mammals together do something the separate parts cannot, and I promised to come back to it. Anyone who thought of emergence at that point, I wrote, had been paying close attention. Emergence is the phenomenon whereby a coherent system displays properties that are not present in the separate parts. Anyone who reads polyvagal theory as a description of an integrated regulatory system sees in it an emergent layer: co-regulation, a sense of social safety, prosody, and affective attunement as properties that the whole system brings forth, not the separate parts.

One question finally remains hanging. In recent years Porges himself already shifted towards a language of repurposing. Given this movement, when would he himself have taken the step to the concept of exaptation?

Afterword

The exaptation perspective does, as I see it, three things at once in the polyvagal debate.

Firstly, it resolves a pseudo-opposition that has kept the discussion in a stalemate for years: the choice between mammalian uniqueness and evolutionary continuity. Both sides have been right, only at different levels, and the concept of exaptation provides the language to make that difference explicit.

Secondly, it shifts the heaviest claim of polyvagal theory from a vulnerable anatomical level, where Taylor and his colleagues stand empirically strong, to a synthesis level that is well defensible empirically. What is really organized differently in mammals is not the presence of separate building blocks, but the integration of face, voice, and heart into one coherent regulatory system. That claim does not stand or fall with the question whether certain vagal fibers already occur in the lungfish.

Thirdly, and this seems paradoxical but it is not, it actually makes polyvagal theory more testable than in its original form. The claims that remain are about what is measurable and researchable in humans: the degree to which face, voice, and heart respond to one another; the working of co-regulation; and the relationship between vagal tone and social behavior. These are empirical questions, not evolutionary claims that withdraw from testing.

What exaptation does not do, and I want to be honest about this, is remove all criticism of polyvagal theory. There are still open methodological questions, such as how ventral vagal activity can best be measured. And the specific phylogenetic claims around the evolutionary reorganization of vagal circuits are plausible but less firmly underpinned than the anatomical part of the theory. However, whether the picture of integration that Porges sketches is really realized neurally remains an open empirical question.

But for the evolutionary part of the debate, precisely where the PVT community has so far responded least convincingly, exaptation offers what the debate needs: a reformulation in which no winner or loser is designated, but both sides are reconciled at a higher level. And it is not without significance that Porges himself has, since 2021, been moving in that direction with his language of “repurposing.” He does not use the word exaptation, but he says something that lies very close to it. This article makes that movement explicit and places it within an evolutionary concept that biology has been working with since 1982.

One observation to finish. Perhaps the most lasting contribution of this whole exercise is not even the exaptation argument itself, but the three-layer structure that comes with it: evolutionary, neurobiological, and functional. That is no longer an exaptation-technical matter but a framework of thought that can also help, in other debates in the polyvagal literature, to disentangle confusions between levels. If anything from this piece is going to take on a life of its own in the discussion, I suspect it may lie there.

If you found this article worth reading (you did, I hope?) and (not yet) feel like getting a paid subscription, you can always treat me to a cappuccino!

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References

Berta, A., Sumich, J. L., & Kovacs, K. M. (2015). Marine mammals: Evolutionary biology (3rd ed.). Academic Press / Elsevier.

Campbell, H. A., Leite, C. A. C., Wang, T., Skals, M., Abe, A. S., Egginton, S., Rantin, F. T., Bishop, C. M., & Taylor, E. W. (2006). Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake, Crotalus durissus terrificus. Journal of Experimental Biology, 209(14), 2628–2636. https://doi.org/10.1242/jeb.02278

Doody, J. S., Burghardt, G. M., & Dinets, V. (2023). The evolution of sociality and the polyvagal theory. Biological Psychology, 180, 108569. https://doi.org/10.1016/j.biopsycho.2023.108569

Doody, J. S., Dinets, V., & Burghardt, G. M. (2021). The Secret Social Lives of Reptiles. Baltimore: Johns Hopkins University Press.

Gould, S. J., & Vrba, E. S. (1982). Exaptation, a missing term in the science of form. Paleobiology, 8(1), 4–15.
https://doi.org/10.1017/S0094837300004310

Grigg, G., Nowack, J., Bicudo, J. E. P. W., Bal, N. C., Woodward, H. N., & Seymour, R. S. (2021). Whole-body endothermy: Ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians. Biological Reviews, 97(2), 766–801.
https://doi.org/10.1111/brv.12822

Grossman, P. (2023). Fundamental challenges and likely refutations of the five basic premises of the polyvagal theory. Biological Psychology, 180, 108589. https://doi.org/10.1016/j.biopsycho.2023.108589

Grossman, P., & Taylor, E. W. (2007). Toward understanding respiratory sinus arrhythmia: Relations to cardiac vagal tone, evolution and biobehavioral functions. Biological Psychology, 74(2), 263–285. https://doi.org/10.1016/j.biopsycho.2005.11.014

Halder, G., Callaerts, P., & Gehring, W. J. (1995). Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila. Science, 267(5205), 1788–1792.
https://doi.org/10.1126/science.7892602

Popper, K. R. (1959). The Logic of Scientific Discovery. London: Hutchinson.

Porges, S. W. (1995). Orienting in a defensive world: Mammalian modifications of our evolutionary heritage. A Polyvagal Theory. Psychophysiology, 32(4), 301–318.
https://doi.org/10.1111/j.1469-8986.1995.tb01213.x

Porges, S. W. (2011). The Polyvagal Theory: Neurophysiological foundations of emotions, attachment, communication, and self-regulation. New York: W.W. Norton.

Porges, S. W. (2021). Polyvagal Theory: A biobehavioral journey to sociality. Comprehensive Psychoneuroendocrinology, 7, 100069. https://doi.org/10.1016/j.cpnec.2021.100069

Porges, S. W. (2022). Polyvagal Theory: A science of safety. Frontiers in Integrative Neuroscience, 16, 871227.
https://doi.org/10.3389/fnint.2022.871227

Porges, S. W. (2023). The vagal paradox: A polyvagal solution. Comprehensive Psychoneuroendocrinology, 16, 100200. https://doi.org/10.1016/j.cpnec.2023.100200

Shubin, N. (2008). Your Inner Fish. New York: Pantheon Books.

Taylor, E. W., Wang, T., & Leite, C. A. C. (2022). An overview of the phylogeny of cardiorespiratory control in vertebrates with some reflections on the ‘Polyvagal Theory’. Biological Psychology, 172, 108382. https://doi.org/10.1016/j.biopsycho.2022.108382

Last week, the first part of this two-part series was published, in which the experiences of clients and professionals with the polyvagal theory took centre stage. In this new article, I expose a pattern. The polyvagal theory (PVT) may be subjected to critical scrutiny; that is both valuable and necessary. But the burden of proof that some demand of it stands in stark contrast to the standards applied elsewhere in science. That inconsistency deserves attention because it gives the impression that more is at play than purely scientific motives1.

To make that pattern visible, I do not begin with the PVT but with a number of medical and psychological treatments that have been standard practice for decades. Because anyone who wants to understand the bar being set for the PVT must first see how low that bar lies elsewhere2. Many treatments applied daily in clinics and practices rest on a foundation that is, on closer inspection, rather shaky. Treatments that work are sometimes only proven to do so years later, and treatments that appeared to work are sometimes only found to be ineffective years down the line.

Let me first give a few examples of how low the bar in science sometimes lies. The contrast with what critics demand of the PVT will then be all the sharper.

Paracetamol: still a mystery

Paracetamol is the most widely used painkiller in the world. You can buy it at any pharmacy without a prescription. And yet scientists still do not know precisely how it works.

What we do know: paracetamol does not work like most other painkillers. Ibuprofen and aspirin reduce inflammation by targeting a specific process in the body. Paracetamol barely does this at all. How it relieves pain remains incompletely understood. There are indications that a breakdown product of paracetamol, formed in the brain, acts on the pain system via pathways that normally respond to cannabis-like substances in the body (Högestätt et al., 2005; Mallet et al., 2023). But even that has not been proven. Multiple processes are likely at work simultaneously.

No one demands that paracetamol be withdrawn from the market until its mechanism is fully elucidated, and that would be absurd; the drug helps people, that much is beyond doubt. But remember this example. I will return to it.

Lithium: gold standard without a golden explanation

For people with bipolar disorder, in which moods can swing violently between deep depression and mania, lithium is considered one of the most effective medications available. It is also used in recurrent depression. There is strong evidence for its role in stabilizing mood and reducing the risk of suicide (Cipriani et al., 2013). But what does lithium actually do in the brain? That is less clear. It affects dozens of processes in the body simultaneously. Which of those processes explains its efficacy remains a matter of scientific debate (Malhi et al., 2013). We prescribe it. It works, but we do not know precisely how. No problem (apparently).

EMDR: are the eye movements actually necessary?

EMDR is a well-researched therapy for trauma and is now included in clinical guidelines worldwide. That it works is not in dispute. But the specific element to which EMDR owes its name, the eye movements, very much is. When researchers compared EMDR with eye movements to EMDR without eye movements, an initial large-scale analysis found no difference in effectiveness (Davidson & Parker, 2001). A later analysis did find a modest difference (Lee & Cuijpers, 2013), but that study contained a number of weaknesses that make its conclusions less conclusive. A broad overview of 76 studies concluded that the evidence for the specific contribution of eye movements is not unequivocal (Cuijpers et al., 2020). The most widely supported explanation now points to working memory load: simultaneously holding a memory and performing a mental task reduces the emotional charge of that memory. This can be achieved by means other than eye movements.

Does EMDR work? Yes. But not for the reason embedded in its name. And yet it appears in every trauma guideline.

Attachment theory: useful, influential, and less proven than it appears

Bowlby’s attachment theory is one of the most influential models in twentieth-century psychology. The core idea is recognizable and intuitive: the bond a child forms with its caregiver(s) in the early years lays a foundation for how that person later navigates relationships, handles stress, and regulates themselves. Therapists worldwide work with it. Clients recognize themselves in it. It gives language to something that is otherwise difficult to articulate.

But the scientific status of attachment theory is shakier than its broad acceptance suggests. The original categories—secure, anxious-avoidant, anxious-ambivalent, and disorganized—are based on the Strange Situation, a laboratory procedure from 1969 in which a toddler is separated from its caregiver for a few minutes (Ainsworth & Wittig, 1969). The question is, how representative is such a brief laboratory situation of the full complexity of a caregiving relationship? And how well does what you measure in that moment actually predict how someone will manage relationships as an adult? The answer: less well than you might expect (Fraley, 2002). Whether early attachment actually causes later difficulties, rather than simply being associated with them, has not been convincingly demonstrated3.

And then there is the oversimplification. In popular psychology, attachment theory has become an explanatory system capable of accounting for almost anything: relationship anxiety, avoidance, burnout, addiction. That is not what Bowlby described, and it does not do the theory justice. A useful framework becomes a catch-all concept and, in the process, becomes simultaneously less useful and harder to test.

Familiar? It is a pattern we also see with the PVT…

Herniation and knee surgery: unnecessary?

This is where things become genuinely uncomfortable. Lumbar disc surgery was performed on a large scale for many years and still is in many countries. The reasoning is intuitively plausible: there is pressure on a nerve, we relieve that pressure, and the pain disappears. Only, on closer inspection, that story holds up only in part.

A large-scale American study, the so-called SPORT trial, compared surgery with conservative treatment, in this case physiotherapy and watchful waiting. The conclusion: in the long term, surgery barely outperformed conservative management (Weinstein et al., 2006). Moreover, it turns out that disc herniations can resolve spontaneously in many patients without any intervention. And there is something else striking: a substantial proportion of the general population has demonstrable disc herniations on MRI scans without experiencing any pain whatsoever. The structural abnormality on the scan and the patient’s complaint are only weakly correlated. The scan is used to justify the procedure, while that same scan does not adequately explain why the person is in pain.

Then there is the parallel with knee arthroscopy for osteoarthritis, a procedure in which cartilage in the knee is trimmed or cleaned. In 2002, researchers published a study in the prestigious New England Journal of Medicine in which some patients underwent a sham operation: an incision was made, but nothing was done inside the knee. After two years, these patients had the same outcomes as those who had undergone the actual procedure (Moseley et al., 2002). The operation performed no better than the expectation of having been operated on. It still took years before practice changed.

Here, then, not only is the explanation lacking; the active mechanism itself is absent. And yet the surgery continued for years.

Antidepressants and the serotonin story

For a long time, the dominant explanation for depression was the so-called serotonin deficiency hypothesis: depression was said to be caused by insufficient serotonin in the brain, and antidepressants, the so-called SSRIs, were supposed to correct that deficit. This explanation appeared in patient information leaflets, was conveyed by general practitioners, and gave people an understandable account of what was happening to them.

In 2022, a large umbrella review summarized all available research in this area. The conclusion was unambiguous: there is no consistent scientific evidence that depression is caused by a serotonin deficiency (Moncrieff et al., 2022). SSRIs help some patients; that is not in dispute. But the explanation that was proclaimed with such confidence for decades turns out to be wrong. Whether a treatment works and whether the theory behind it is correct are two different questions. And here, the theory was not correct.

A ruptured aneurysm: when the bar disappears entirely

No randomized controlled trial (the gold standard for establishing the safety and effectiveness of a treatment) has ever been conducted in patients with a ruptured abdominal aortic aneurysm (a tear in the body’s main artery, usually in the abdomen, which causes the patient to bleed to death internally unless surgery is performed). The control condition, “let’s wait and see,” has never passed an ethics committee, and it never will. And yet surgeons worldwide operate daily on patients with a rupturing aorta, without anyone arguing that this is unethical lacking RCT evidence. Clinical logic suffices: the artery ruptures, the patient bleeds to death, and we intervene. Proven mechanism? Check. Proven efficacy via randomized trial? Well, no, but no one loses sleep over it.

It is just one example. But it illustrates something: the call for evidence is not always equally loud and not always equally consistent. Sometimes clinical logic may suffice. Sometimes common sense is permitted to take precedence over protocol. It is simply a pity that this latitude is not extended with equal generosity to everyone.

The double standard and how it is maintained

Disc surgery was performed and reimbursed on a large scale for years, while evidence for its added value was already under pressure. An incorrect explanation for depression was conveyed to patients for decades. EMDR appears in every guideline, while its most distinctive element remains scientifically unsettled. No one seems particularly troubled by any of this.

A theory about the functioning of the autonomic nervous system, with a solid grounding in neuroanatomy, recognized in clinical practice, and supported by a growing body of empirical research (see, for example, Porges, 20254), must, according to some, meet stricter requirements before it can be taken seriously.

It is therefore time to subject the criticism itself to critical scrutiny. Because the way in which the PVT is judged is not arbitrary. This situation is maintained by a combination of structural mechanisms and by the content and tone of the criticism itself. I identify six aspects:

The first is publication bias. Studies with positive results are published more frequently than studies with negative results. For established treatments, this means failures remain invisible for longer. For new theories such as the polyvagal theory, it means every critical voice finds a platform, while supporting evidence is subjected to stricter scrutiny.

The second is the question of who actually decides what constitutes “sufficient proof.” Clinical guideline committees, health insurers, and journal editorial boards—all of them have their interests, blind spots, and networks. The polyvagal theory has no powerful institutional lobby behind it. Paracetamol and SSRIs do. That has consequences for which treatments and theories become mainstream and which must first prove themselves entirely5.

The third is the shifting goalposts. The knee arthroscopy example showed that a sham operation worked just as well as a real one. The effect consisted entirely of the expectation of recovery following the (sham) procedure. But when a PVT-informed therapist does something that helps, and clients recover, regulate, and feel what they had not felt for a long time, they are asked to demonstrate the mechanism, or it is said that working in this way is unethical. The standard shifts according to what is convenient.

The fourth is the language of evidence itself. “Not evidence-based” sounds like an objective judgment: neutral, scientific, beyond question. But the term is not neutral. The dominant model of scientific evidence was developed for standardized interventions: a pill, a protocol, or a procedure. That model works reasonably well for medications or surgery. It works less well for explanatory theories about physiological processes, relational safety, or the functioning of the autonomic nervous system. Theories that do not describe a single intervention but an underlying principle, such as the PVT, which does not prescribe what a practitioner should do but explains why people respond the way they do under pressure, in connection, in danger, and in safety. Those who use “evidence-based” as the sole standard without acknowledging its limitations are, from the outset, excluding part of reality. And calling that objectivity.

The fifth is the reversed burden of proof. In the debate around the PVT, the claim is regularly made that polyvagal-informed practice is harmful. But that claim has never been substantiated with evidence. No one has presented documented cases. No one has cited formal complaints. No one has provided case reports. The burden of proof for efficacy is stringently demanded, but the burden of proof for the alleged harm caused is not delivered. That is not what we call scientific reasoning; it is an unsubstantiated claim and a line of argument that does not apply to itself the very norm it insists upon. That is dishonest and perhaps even lacking in integrity.

Which brings us to the ethical dimension. In the debate, working from a polyvagal perspective is sometimes described as outright unethical because the theory “does not hold” or is insufficiently proven. That is a bold claim. A claim that, applied consistently, would also require removing paracetamol from the market, prohibiting disc surgery, and striking EMDR from clinical guidelines. No one draws that conclusion there. That raises the question of whether it is ethically defensible to assert that working with the PVT is unethical, and therefore who is actually violating an ethical norm here.

The way in which criticism is currently being expressed does not sound like science. It sounds more like politics. And those who look more closely at the tone, the consistency, and the targeted nature of the criticism of the PVT may well ask themselves whether scientific integrity is the driving force here, or something else entirely6.

Read here part 1 of this two-part series, in which I invite clients and professionals to share their experiences with the polyvagal theory, both positive and negative.

If you found this article worth reading and (not yet) feel like getting a paid subscription, you can always treat me to a cappuccino!

OK, I'll buy you a cappuccino!

References

Ainsworth, M.D.S. & Wittig, B.A. (1969). Attachment and exploratory behavior of one-year-olds in a strange situation. In B.M. Foss (red.), Determinants of infant behaviour (Vol. 4, pp. 111–136). Methuen.

Cipriani, A., e.a. (2013). Lithium in the prevention of suicide in mood disorders: updated systematic review and meta-analysis. BMJ, 346, f3646. https://doi.org/10.1136/bmj.f3646

Cuijpers, P., e.a. (2020). Eye movement desensitization and reprocessing for mental health problems: a systematic review and meta-analysis. Cognitive Behaviour Therapy, 49(3), 165–180. https://doi.org/10.1080/16506073.2019.1703801

Davidson, P.R. & Parker, K.C.H. (2001). Eye movement desensitization and reprocessing (EMDR): a meta-analysis. Journal of Consulting and Clinical Psychology, 69(2), 305–316. https://doi.org/10.1037/0022-006X.69.2.305

Fraley, R.C. (2002). Attachment stability from infancy to adulthood: Meta-analysis and dynamic modeling of developmental mechanisms. Personality and Social Psychology Review, 6(2), 123–151. https://doi.org/10.1207/S15327957PSPR0602_03

Grossman, P., e.a. (2026). Why the polyvagal theory is untenable. An international expert evaluation of the polyvagal theory and commentary upon Porges, S.W. (2025). Clinical Neuropsychiatry.
https://doi.org/10.36131/cnfioritieditore20260110

Högestätt, E.D., e.a. (2005). Conversion of acetaminophen to the bioactive N-acylphenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system. Journal of Biological Chemistry, 280(36), 31405–31412.
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Kok, B.E. & Fredrickson, B.L. (2010). Upward spirals of the heart: Autonomic flexibility, as indexed by vagal tone, reciprocally and prospectively predicts positive emotions and social connectedness. Biological Psychology, 85, 432–436.
https://doi.org/10.1016/j.biopsycho.2010.09.005

Lee, C.W. & Cuijpers, P. (2013). A meta-analysis of the contribution of eye movements in processing emotional memories. Journal of Behavior Therapy and Experimental Psychiatry, 44(2), 231–239. https://doi.org/10.1016/j.jbtep.2012.11.001

Malhi, G.S., e.a. (2013). Potential mechanisms of action of lithium in bipolar disorder. CNS Drugs, 27(2), 135–153.
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Mallet, C., Desmeules, J., Pegahi, R. & Eschalier, A. (2023). An updated review on the metabolite (AM404)-mediated central mechanism of action of paracetamol (acetaminophen): experimental evidence and potential clinical impact. Journal of Pain Research, 16, 1081–1094. https://doi.org/10.2147/JPR.S393809

Moncrieff, J., e.a. (2022). The serotonin theory of depression: a systematic umbrella review of the evidence. Molecular Psychiatry, 28, 3243–3256. https://doi.org/10.1038/s41380-022-01661-0

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Porges, S.W. (2026). When a critique becomes untenable: A scholarly response to Grossman et al.’s evaluation of polyvagal theory. Clinical Neuropsychiatry.
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Quintana, D.S., Guastella, A.J., Outhred, T., Hickie, I.B. & Kemp, A.H. (2012). Heart rate variability is associated with emotion recognition: Direct evidence for a relationship between the autonomic nervous system and social cognition. International Journal of Psychophysiology, 86(2), 168–172.
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A theory that does not reach people changes nothing. The polyvagal theory (PVT) has reached a worldwide audience over the past thirty years, and a question that has been on my mind for some time is what those people have gained from it.

In debates around the PVT, the suggestion has recently been made with some regularity that working from a polyvagal-informed perspective is unethical or even harmful. Characterizations that do not fit my experience at all1, but that I am not willing to simply dismiss. There is, after all, a chance that there is some truth to them—and these suggestions, made without any supporting evidence from client stories, made me not only angry but also curious.

In the comments below this article, I would therefore like to collect experiences. From clients, therapists, colleagues, and participants who attended a training with me. I am doing this partly to illustrate the value of the polyvagal theory for clinical practice with concrete examples and partly to collect cases in which harm may have been caused by the polyvagal theory. To my knowledge, this has not been done systematically before, which makes this call all the more relevant.

The article you are about to read forms, together with my article on evidence, double standards in science, and the ethics of criticism, a two-part series that aims to take an honest look at what the PVT gives people and where things go wrong—because decisions about what professionals may or may not use must be grounded in facts, not unfounded claims, and because the clinical value of the PVT is too great to lose to an unfair debate.

Words for what had no name

One of the most common reactions from people encountering the PVT for the first time is a variation on the same theme: “Finally, I understand why I do what I do.” The account of how the autonomic nervous system works is more than a cognitive explanation; it provides recognition and often feels like a relief. Exculpatory is a word that fits here.

People who spent years believing they were “weak” because they froze in stressful situations learn that freezing is not a character flaw but a biological survival response—older than language and older than human consciousness. People who describe themselves as “always switched on” recognize sympathetic activation as something their nervous system has learned, not something they are. The shift from judgment—and often self-judgment and shame—to understanding is, for many people, the beginning of recovery (Porges, 2011).

A client who worked with exercises developed by Deb Dana described it this way: “It was an eye-opener to understand why my nervous system reacts the way it does. I was constantly in a state of activation and felt empty by the end of the day. Once I understood where I was on the ladder (the ladder is a tool developed by Dana to explain the PVT to clients), I started to relate to myself differently. My brain catastrophized far less.” (Muller & Vu, 2022)

In the consulting room

For therapists working with trauma, the PVT has fundamentally shifted the focus from the story told in words to the physiology—the story the body tells. From “what happened” to “what is the body doing now.” That is not a small change.

Polyvagal-informed practitioners learn to work more consciously with cues of danger and safety: in the treatment room and in the way they make contact—through posture and tone of voice, for instance. The therapeutic relationship becomes less about words and more about a physiological process of co-regulation (Porges & Dana, 2018). Early research suggests that the quality of the therapeutic bond is associated with clients’ autonomic regulation and that heart rate variability has something to say about how safe a client experiences the relationship—and even about the outcome of therapy (Blanck et al., 2019).

This has practical implications. Therapists working from a polyvagal perspective attend to vocal prosody, eye contact, and the layout of the room. They understand that a client who “cannot make contact” is not unwilling but physiologically unavailable, and they do not fall into the trap of applying more pressure or asking more questions. They work with the nervous system rather than against the behaviour.

Children, schools, and early development

The PVT has also found its way beyond the consulting room—into education, childcare, and neonatology. Pediatrician Marilyn Sanders and child psychiatrist George Thompson describe how polyvagal-informed care can make a difference for children who have experienced early trauma or attachment difficulties. Not by talking more, but by organizing safety physiologically. Caregivers who learn how a child’s nervous system signals and processes safety can have a significant positive influence on that child’s development (Sanders & Thompson, 2022).

In Spain, 585 primary school pupils took part in a breathing and heart rate variability training program based on polyvagal principles. Afterward, the children showed significantly lower levels of anxiety and stress (Ruiz-Aranda et al., 2022).

All of this research points consistently in one direction: working with the nervous system pays off, even outside the consulting room.

The Safe and Sound Protocol

One of the most practical applications of the PVT is the Safe and Sound Protocol (SSP), a listening program using filtered music that trains the auditory system to recognize human vocal frequencies as safe while becoming less attuned to lower tones (associated with predators) and higher tones (associated with alarm calls). It was developed by Porges himself and is now used worldwide.

Initial studies with adults with autism showed improvements in social responsiveness, particularly in the area of social awareness (Kawai et al., 2023). These are pilot studies with small groups; larger, controlled studies are needed. People with anxiety, ADHD, and trauma report in practice a reduction in sensory hypersensitivity, improved emotional regulation, and a greater capacity for connection—experiences that are illustrative, not scientific proof.

The SSP is, of course, not a miracle cure. Some people find the stimulation too intense, particularly when the build-up is too rapid. This underlines something essential: every tool requires skilled use. And here, I believe, lies a mechanism behind some criticism directed at the PVT. Negative experiences with the SSP travel well in professional circles and can cast a shadow over the entire polyvagal theory. It is an understandable mechanism, one we encounter more broadly, and one where double standards are sometimes applied. I will address this in depth in next week’s article.

Somatic Experiencing

Another approach that connects seamlessly with polyvagal principles is Somatic Experiencing® (SE), developed by Peter Levine. Where the PVT describes how the nervous system responds to danger and safety, SE offers a method for gently discharging survival responses that have become stuck. Levine observed that animals in the wild literally shake and tremble after a threatening situation—a physiological discharge of accumulated mobilization energy. In humans, this discharge is often blocked. SE works with precisely that blockage: not by reliving the trauma, but by slowly guiding the nervous system towards completion of an interrupted response (Levine, 1997).

What connects SE and the PVT is a shared starting point: the body is not the problem, but the pathway to recovery. SE practitioners work with what Eugene Gendlin, founder of focusing, called the “felt sense”—a concept that Levine adopted and placed at the heart of his method. The felt sense might be described as the subtle, bodily awareness that precedes emotions and thoughts (Gendlin, 1978). By attending to this, at a pace the nervous system can manage, space opens up for regulation that talking alone cannot achieve. Clients often describe a feeling of relaxation after SE sessions that they had not known for a long time—not as an achievement, but as something the body did by itself once it had the space and safety to do so.

From a polyvagal perspective, this is no coincidence. SE is most effective when the client has sufficient ventral vagal tone to tolerate the experience—the zone in which activation remains manageable and integration becomes possible (Dana, 2018); what Daniel Siegel called the “window of tolerance” (Siegel, 1999) and what Levine described in comparable terms. A nervous system deeply in shutdown cannot yet handle discharge. The therapist therefore works first on safety and contact, then on regulation and mobilization, and only then on completion and integration. This is precisely the sequence that the polyvagal hierarchy predicts: ventral regulation as a prerequisite for everything that follows.

SE and the PVT describe essentially the same landscape: the PVT as the map2, SE as the route. Levine and Porges have been friends for decades, and Levine embraced the PVT early on, because it gave him an explanation for what he had been observing in his clients for years3.

Creativity, movement, and the arts therapies

The PVT has also provided a theoretical foundation for fields that had long worked with the body and the senses but could not always account for why. Art therapy, psychomotor therapy, music therapy, and dance—all of these work directly on the autonomic nervous system through sensory and movement experiences. The PVT offers a neuroscientific language for this.

Researchers at HAN University of Applied Sciences in Nijmegen describe how polyvagal principles—attention to physical and sensory experience, co-regulation, and working from a place of safety—connect seamlessly with what arts therapists and psychomotor therapists were already doing. The theory gives their work an academic language and deepens the understanding of why certain interventions work (Haeyen, 2024).

What the PVT offers that cognitive models do not

People who have spent years—sometimes many years—in cognitive therapy and “know” that their anxiety is irrational but continue to feel it often recognize something important in the polyvagal theory: thinking alone does not shift your physiology sufficiently towards safety. You cannot reason yourself out of a state of shutdown. You cannot argue away the flight response. The nervous system operates at a level that words do not reach, and it calls for a different approach.

Porges captured this in a reformulation of Descartes: not “I think, therefore I am,” but “I feel myself, therefore I am” (Porges, 2022). It sounds philosophical, but it speaks to something many people in therapy are missing: recognition that the body is not the enemy but the guide. That the reactions standing in their way are not weaknesses, but marks left by something that once helped them survive. And then there is something else many people recognize: the feeling of not truly feeling oneself, as if watching one’s own life from a distance4. From a polyvagal perspective, this is an understandable phenomenon: a nervous system that has closed itself off to survive.

This reframe—from pathology to adaptation (from disorder to adjustment)—is for many clients and therapists, the core of what the PVT offers. Not a diagnosis, but a story that is recognized and that can be worked with.

My own experience

I have now been working for over six years as a mindfulness therapist in the day treatment unit of the Psychiatry Department at Gelre Hospital in Apeldoorn, the Netherlands. I provide group and individual mindfulness sessions, into which I regularly weave elements of Somatic Experiencing. The people who come to the groups and individual sessions have, alongside a psychiatric diagnosis, a physical component to their presentation—which is precisely why they are seeing a hospital psychiatrist. For nearly all of them, the idea of feeling into their body is, to put it mildly, something they would rather avoid. They have become unaccustomed to it, and have a disturbed relationship with their body, ranging from chronic frustration to outright hatred of it.

In every group, after several weeks, I explain the polyvagal theory. I do so using simple language—something I have also had to learn—and fill the whiteboard with drawings and notes.

One of the most common reactions to a whiteboard full of diagrams is, “Well, you can put my name up there,” meaning recognition. Things click into place. People see connections, better understand why they react the way they do, and become more convinced that their nervous system is actually giving a “normal” response to the abnormal events that have occurred in their lives. Whether it was abuse, bullying, an accident, an emergency operation, serious illness, or another overwhelming event—the body has lost its sense of safety and has adjusted—sensibly, but unfortunately often with unwanted consequences for the here and now—by moving more readily into a defensive autonomic state. Outside conscious control or will, intending to protecting.

In my view, the polyvagal theory is enormously helpful. It gives direction to sessions and motivates people to practice—even though learning to feel in one’s body again is demanding—with the meditations I offer and to engage with exercises during our sessions, to reflect on them afterward, and to gradually become better at recognizing and growing signals of safety.

That said, I have regularly noticed that clients did not fully understand my explanation, and I have had to learn which words and exercises work and which do not. To my knowledge, I have been able to resolve the resulting misunderstandings in the great majority of cases, and over time I have practiced increasingly at explaining the PVT in plain language without losing too much nuance. There is probably a phenomenon here that can never be entirely prevented: how is your explanation heard and remembered?

Share your story

All of this is important information. Not (or not yet?) as scientific evidence, but as living knowledge—which I will also share with the Polyvagal Institute Netherlands.

The road to evidence-based often runs through practice-based.

Your stories help me understand how the PVT really lands in practice, and they form a richer basis for conversation than abstract debates about neuroanatomy alone.

And also: where did things go wrong?

My working hypothesis—and I call it explicitly a hypothesis, not a prejudice—is that when polyvagal-informed practice causes harm, the cause is not the theory itself. I suspect it will often involve insufficiently trained therapists applying the theory too simplistically. Or misrepresentation of the PVT: over-popularization in which nuance is lost and people are confronted with overly confident claims. Or general therapeutic incompetence that has nothing to do with the PVT but that damages both the client and the theory’s reputation. Stephen Porges himself has described that the PVT is sometimes applied in wellness and coaching contexts in ways that do not reflect the scientific depth of the theory and that this is a matter of training and responsibility in translating the theory into practice, not of the theory itself (Porges, 2025).

In all of these cases, harm can occur, and I can well imagine that it does. That is serious, and every such case is one too many. But misinterpretation of the theory and therapist incompetence cannot be attributed to the polyvagal theory itself.

But my hypothesis is a hypothesis. And hypotheses deserve to be tested. So if you—as a client, therapist, supervisor, or trainer—know of situations in which polyvagal-informed practice demonstrably contributed to harm, I would like to hear about them. Concrete cases, documented situations, formal complaints. It is important to start collecting this to learn from it. Because if that evidence exists, I want to know it. And if it does not exist—that too is an answer to the question of how dangerous the polyvagal theory actually is. An answer that deserves to be heard.

Read here part two of this two-part series on evidence, double standards in science, and the ethics of criticism.

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References

Blanck, P., Stoffel, M., Bents, H., Ditzen, B., & Mander, J. (2019). Heart rate variability in individual psychotherapy: Associations with alliance and outcome. Journal of Nervous & Mental Disease, 207(6), 451–458. https://doi.org/10.1097/NMD.0000000000000994

Dana, D. (2018). The polyvagal theory in therapy: Engaging the rhythm of regulation. W.W. Norton & Company.

Gendlin, E.T. (1978). Focusing. Everest House.

Haeyen, S. (2024). A theoretical exploration of polyvagal theory in creative arts and psychomotor therapies for emotion regulation in stress and trauma. Frontiers in Psychology, 15, 1382007. https://doi.org/10.3389/fpsyg.2024.1382007

Kawai, H., et al. (2023). Initial outcomes of the Safe and Sound Protocol on patients with adult autism spectrum disorder: Exploratory pilot study. International Journal of Environmental Research and Public Health, 20(6), 4862. https://doi.org/10.3390/ijerph20064862

Levine, P. (1997). Waking the tiger: Healing trauma. North Atlantic Books.

Muller, R.T. & Vu, L.H. (2022). Polyvagal theory: An approach to understanding trauma. Psychology Today, June 2022. https://www.psychologytoday.com/us/blog/talking-about-trauma/202206/polyvagal-theory-approach-understanding-trauma

Porges, S.W. (2011). The polyvagal theory: Neurophysiological foundations of emotions, attachment, communication, and self-regulation. W.W. Norton & Company.

Porges, S.W. (2022). Polyvagal theory: A science of safety. Frontiers in Integrative Neuroscience, 16, 871227. https://doi.org/10.3389/fnint.2022.871227

Porges, S.W. & Dana, D. (Eds.) (2018). Clinical applications of the polyvagal theory: The emergence of polyvagal-informed therapies. W.W. Norton & Company.

Porges, S.W. (2025). Polyvagal theory: Current status, clinical applications and future directions. Clinical Neuropsychiatry, 22(3), 169–184. https://doi.org/10.36131/cnfioritieditore20250301

Ruiz-Aranda, D., et al. (2022). Reducing anxiety and social stress in primary education: A breath-focused heart rate variability biofeedback intervention. International Journal of Environmental Research and Public Health. PMC9407856. https://doi.org/10.3390/ijerph191610181

Sanders, M.R. & Thompson, G.S. (2022). Polyvagal theory and the developing child: Systems of care for strengthening kids, families, and communities. W.W. Norton & Company.

Siegel, D.J. (1999). The developing mind: How relationships and the brain interact to shape who we are. Guilford Press.

Over the years, Grandmaster William C. C. Chen has never stopped developing. There is a remark of his that I heard him make somewhere in the 1990s and will not easily forget: “After 50 years of practicing Tai Chi, I discovered something.” He would then share this discovery, and we would spend the entire day exploring it in our training, trying to find or apply it ourselves. It is the hallmark of a true master: always remaining a student.

William Chen was always a very practically oriented Tai Chi teacher, with a strong focus on martial applications and boxing. The subject of health was not something he emphasized greatly—that began to change around 2012 and beyond. In 2015 he wrote the article below, which he gave me permission to translate, with assistance from my teacher, Master Laura Stone.

The translated article appeared in TQT Magazine, which no longer exists. I felt it was worth making it available to the public once more. Voilà:

Tai Chi Practice and the Prevention of Heart Disease

The most important steps in preventing heart disease are movement, together with healthy nutrition, healthy sleep, and healthy thinking. Exercise helps to relax the muscles of the rib cage and give the organs sufficient room to function.

Improving the lubrication and oxygenation of the organs is one of the fundamental ways to remove bacteria, viruses, and toxins and contributes to the better functioning and health of all organs—especially to the vitality of the heart.

There is nothing magical about the positive effects of the magical art of Tai Chi practice on heart disease. It is simply a matter of relaxing the muscles of the rib cage while the arms float upward and the elbows move slightly outward to keep the armpits open, thereby increasing the volume of the torso. This helps the organs to function effectively through the enlarged space in the chest cavity. At the same time, deep breathing provides sufficient oxygen to the blood and removes carbon dioxide from the body, allowing us to live long and in good health. This is the primary purpose of the slow tempo of the movements.

Synchronizing the soft, slow movements with deep diaphragmatic breathing is one of the best ways to prevent heart disease. Exhaling calms the nerves and relieves muscular tension. When the muscles of the rib cage are relaxed, the arms float upward and the armpits open slightly. The result is an increase in the volume of the torso, giving the organs more room to function optimally.

Deep diaphragmatic breathing brings more oxygen into the lungs than ordinary breathing. More oxygen-rich blood from the heart stimulates the functioning of the immune system, making it easier for the body to detoxify. We aim to keep the heart functioning well.

The heart is the hub of the organs, pumping oxygen-rich blood (氣血) throughout the body. All major aspects of fitness, health, and life itself depend on the functioning of the heart. The organs depend on the heart for their proper functioning. Every organ, tissue, and cell in the body depends on the blood pumped by the heart for optimal performance.

Although emotional stress is a natural part of life, the excessive and persistent worry, anxiety, and despondency that accompany stress are highly damaging. Stress causes the muscles of the rib cage to contract. The diaphragm rises and the arms fall against the rib cage. This reduces the volume of the torso, impairing blood flow to the organs and potentially overburdening the heart.

A poorly functioning heart pumps less oxygen and nutrients to the organs and removes fewer waste products, toxins, and carbon dioxide from the body. This inevitably leads to tissue poisoning and organ failure, resulting in a number of heart-threatening conditions.

Heart disease is the leading cause of death in the United States, with nearly 2,000 deaths per day. Each year, approximately 720,000 Americans suffer a heart attack—515,000 of them for the first time, and 205,000 having had a previous heart attack. A major cause of heart disease is excessive strain on the organs. Lack of space and poor circulation of the heart gives rise to disease.

The importance of exercise in preventing heart disease has been repeatedly demonstrated by experts in the field. The CDC Division for Heart Disease and Stroke Prevention (DHDSP), for example, states in its summary of risk factors and recommendations that adults are advised to engage in two and a half hours of physical activity per week.

The Ohio State University Medical Center lists fitness as a means of preventing heart disease. Exercise is nature’s medicine—more powerful than any pharmaceutical in restoring and rejuvenating the human heart and organs.

Daily movement is essential for the heart. Researchers have concluded that exercise is a superior method for keeping our hearts healthy, noting that regular gentle movement is better than short, intense, and more strenuous workouts. Exercise helps to loosen overtaxed muscles throughout the body, allowing everything to function more smoothly and efficiently.

The slow-motion practice of Tai Chi Chuan is strongly recommended by physicians. The slow movements calm the nervous system and relieve excessive preoccupation with worry, anxiety, and despondency. The muscles of the rib cage relax and the volume of the torso increases, creating more space and improving organ function.

Enlarging the space of the torso allows the lungs to function better by enabling a full inhalation and exhalation. At the same time, the toes press into the ground and the fingers push against the resistance of the air, generating a powerful flow of energy through the body. This creates a dynamic jetstream wave effect within the torso, capable of flushing out organ impurities. This is comparable to the water jets in a dishwasher, which rinse the dirt from the dishes and leave them clean and ready to be used again.

The same principle applies to the brain cells. Dr. Maiken Nedergaard, a leading neuroscientist, explains in “The Power of Sleep” (Alice Park, Time Magazine, November 9, 2014) how changes in brain cells during sleep create greater opportunity for cerebrospinal fluid to flow. “It is like a dishwasher rinsing away the dirt,” she writes.

The Tai Chi movements support the return of blood from the legs to the heart. When we take a slow step and place the foot down softly so that the calf muscles remain relaxed, blood can pool in the lower leg. As we gradually shift our weight from heel to toe and press the toes into the ground, the calf muscle pumps the blood upward toward the heart, increasing blood supply to the heart.

This supporting action of the calf muscle in pumping blood toward the heart is important for us. Research shows that “it takes only one heartbeat to pump blood from the heart to the lower legs, but several strong heartbeats to pump it back up to the heart.”

The mechanism of stepping and releasing in Tai Chi Chuan is critically important for the return of blood to the heart while simultaneously improving circulation in the legs. This calf muscle pump is sometimes called the second heart of the body.

Physicians advise airline passengers to stand up and walk around regularly during long flights. It stimulates circulation in the legs but also promotes healthier circulation of the organs in the torso. The cramped seats of modern commercial airlines force the arms against the rib cage, limiting the volume of the torso and compressing the organs together. This prevents the heart from functioning normally.

Good health depends on the organs of the body. When the organs are healthy and strong, ailments and diseases will occur less frequently. We should not allow stress to reduce the volume of the torso, restricting organ function and impairing the heart.

Stress is not always harmful. We sometimes need tension to stimulate us. Positive stress brims with life energy. Many martial artists, athletes, and performers know how to channel stress into high-energy performance. Properly directed stress can truly work in our favor. The ambition to succeed is the feeling of our conscious heart that provides the energy to realize our aspirations.

Negative states of fear, worry, and despondency, on the other hand, are the cause of muscular tension. The muscles of the rib cage contract and pull the diaphragm upward, while the upper arms simultaneously fall against the rib cage. The space available for the organs in the torso diminishes, circulation deteriorates, and hazardous conditions develop that can result in serious heart disease.

Mother Nature has bestowed upon us a metabolic process capable of renewing the organs of the body. Our torso is like the interior of a dishwasher, and the organs are like reusable plates. We must cleanse the organs as frequently as possible, even before toxins begin to accumulate. Regularly cleansing the organs to keep them in optimal condition is our priority.

Happy people are healthier and live longer than unhappy people. When we are happy, the muscles of the rib cage relax. When we are sad, worried, or unhappy, the muscles of the rib cage contract. The limited space in the torso makes it harder for the organs to function.

The muscle-free movements of Tai Chi Chuan arise from releasing and activating the flow of energy, generating a powerful energetic wave through the body while the muscles—particularly those surrounding the arteries—remain relaxed, producing vasodilation. This creates a constant flow of nutrients and oxygen-rich blood throughout the entire vascular system. This powerful internal energy flow extends far beyond organ cleansing; it helps to purify everything in the body.

Relaxing the rib muscles is the best care we can offer our organs, as it enables them to increase the volume of the torso. This promotes the cleansing of the organs so that they can perform their work effectively and helps to keep the heart vital and in peak condition.

The concept of heart disease prevention has its origins in an insight from my teacher, the world-renowned Grandmaster Professor Cheng Man-Ching, who observed, “The organs of cats and dogs are healthier than those of humans, because their organs hang freely in the body as they move about. This helps to lubricate and oxygenate the organs to keep them healthy, in contrast to the unhealthy human organs that often jostle against each other in the body.”

The information I have gathered and researched through my daily practice with students over the past sixty years leads me to this positive conviction: cleansing the organs is the foundation of staying healthy. The analogy of “organ cleansing as a dishwasher” is one I have carried with me for many years.

This article is part of my lifelong dedication to Tai Chi practitioners. The inner practice of Tai Chi Chuan is like cleansing the body from within. Regularly cleansing the organs, cells, arteries, veins, and tissues of the body is of vital importance to the health of the heart. Cleansing through Tai Chi movements can also help to prevent kidney and liver disease, as well as cancer. It is undeniably helpful in reducing other ailments, diseases, and stress.

Daily practice of Tai Chi Chuan, with heart and mind attuned to feeling the flow of energy pulsing through the body, will keep the doctors at bay. Consistent daily practice of these slow movements is particularly helpful in reducing the burden on hospital staff and physicians.

Dutch article: Tai Chi en het voorkomen van hartaandoeningen

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Written by Yang Style T’ai Chi Ch’uan Grandmaster William C. C. Chen. Original publication: Spring 2015, International Magazine of Tai Chi Chuan, Vol. 39, No. 1. Translation: Ronald de Caluwé, with assistance from Laura Stone. Previously published in TQT Magazine, Vol. 3, No. 10, June 2015.

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In the final session of a mindfulness or compassion training, there is always attention for what comes next. Because once you’re on your own after eight weeks of intensive practice, choices have to be made. Recently I wrote about how you might continue after your training. This piece is about a very common stumbling block in meditation.

When practice stalls

Eventually every practitioner encounters it: meditation quietly slips into the background for a while. A busy period at work, worries at home, a trip away—there are plenty of reasons why practice falls by the wayside. Or perhaps simply a break after all those weeks of training.

For me, the practice dip very often falls in the holiday season. And that’s where I learned an important lesson.

Good intentions

When I first felt, years ago, that meditation was truly something for me—that I was benefiting from it and that it had found a permanent place in my life—I wanted to hold onto that feeling at all costs. So I resolved to take my meditation cushion on holiday. So I wouldn’t lose ‘the feeling.’

At that time we went every year to the island of Ameland in our old caravan. A wonderful island, with plenty of time to read and meditate. The cushion was the first thing packed when we loaded the caravan.

Three weeks later, when we got home, it was the last thing to come back out.

Lost everything?

It had been an incredible holiday, as it almost always is on the Wadden Islands. Wonderfully relaxed, books read, hours enjoyed on the beach and at various terraces and beach pavilions. But meditate? Not once.

Despite the lovely holiday, I felt genuinely disappointed. A familiar inner voice made itself heard: now I’ve lost everything, I’ll have to start from scratch; it was all for nothing.

I heard similar things from former participants I spoke with afterward: once the motivation is gone, there’s no point anymore. Too late. You might as well stop. And then comes the self-criticism: Useless. You can’t even keep that up.

When I recognized that in myself, I finally understood just how powerful that mechanism is.

But wait a moment…

Because—what is meditation actually about? What is the essence that all those famous teachers whose books I had studied keep pointing to?

Is meditation really an achievement you build up and can then lose again? Do past results guarantee future ones?

No—meditation is precisely about sitting down each time as if it were the first time. That is precisely the beginner’s mind we want to cultivate. When that truly landed for me, I realized nothing had been lost, and a weight lifted from my shoulders.

What do you actually lose when your practice stalls for a while? And is there a better option than simply starting again, picking up where you left off? No—more than that: it was always the only option you ever had: just begin again.

Make music

If you haven’t played the piano for a while—a metaphor I like to use, and one I’ll work out fully in an article someday—your fingers may feel a little stiff. There may be resistance to lifting the lid again. You might conclude that there’s no point anymore. But you wouldn’t throw away years of piano lessons, would you?

A pianist sits down and plays. And soon notices that the stiffness fades, often sooner than expected. After enough practice, the music lives in you; you pick it up quickly again—your fingers seem to know it too.

Meditation works no differently. You can stop, or you can simply begin again. Whether the last time was yesterday or three months ago. That is the heart of it: beginning again, always. Without seeking a result, without expecting progress, without demanding calm or a quiet mind. And then being surprised to find that the meditation is still there in you.

Welcome back

So: if your practice has lost its momentum and you’re suffering under the illusion that it’s too late—rest assured. You can let go of the self-criticism and simply begin again. Just as every other practitioner does every day, including those whose practice just happens not to have lapsed right now.

In meditation, there is always another chance. With every breath, even.

Or, as the Sufi mystic Rumi wrote:

Come, come, whoever you are!
Wanderer, worshipper, lover of leaving.
It doesn’t matter.

This is not a caravan of despair.

Come, come.
Even if you have broken your vows a thousand times.
Come,
come again,
come!

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There is something paradoxical about meditation: the more you think about it, the further you drift from its essence.

Most people who sit on a meditation cushion for the first time arrive with an expectation. Sometimes that expectation is “relaxation,” sometimes something like “coming back to yourself,” and sometimes “silence”—inner silence. All of that sounds perfectly fitting and adequate, and yet there tends to be an underlying assumption that the brain has a kind of volume knob that you can turn down to zero once you master the right technique.

But the brain “thinks” otherwise. Thoughts simply arise—whether you want them to or not. You might conclude that you’re doing it wrong, but you could also “see” them as evidence that you are alive. The real question is not how to stop your thoughts, but what you “do” in the moment you notice them. That moment is brief, almost invisible; before you “know” it, it has passed. You were briefly caught up in a thought, and now you’re back. That is the entire “work.” Not an empty head, but that fraction of a second in which you return—without fuss, or at least without judgment about the fuss.

Sharon Salzberg calls this a different relationship with thoughts. The word “relationship” deserves attention. It implies that there are two parties who don’t always agree. That can be true of you and your thoughts as well. You don’t have to like your thoughts. You don’t have to believe them either. They are there, they come and they go, they move—and you can be the one who watches, who “registers” them as “things” that exist and with which you need do nothing.

There is, then, a difference between being inside a thought and seeing a thought. The first is what many people consider normal, and in that state they are likely to merge with their thoughts entirely. There is no longer a thought and someone in whom that thought exists—instead, you become the thought; you are the worry about tomorrow, you are the replay of yesterday’s conversation. Seeing a thought asks nothing more than a small measure of distance. The distance that brings clarity. In ACT therapy, the term “defusion” has been coined for this—a felicitous find: becoming disentangled from thoughts.

The space that Salzberg speaks of, which she describes as both peace and freedom, is not something you need to “create.” It is more that you uncover it—because it was already there. Beneath the layers of interpretations, judgments, reactivity, and stories that the thinking mind continuously produces, there is something that simply … is. Without drama or fuss, simply present.

For some people, this is a startling discovery in meditation: that stillness is not reached by overcoming thought but by no longer being completely swept away by it. As I sometimes say, it’s not about being free from thoughts but about becoming free with your thoughts.

You don’t need to be a good meditator. In fact, that’s not really possible. All you need to do is begin—and when you’ve drifted away, which will often happen, simply begin again. That’s it. Beginning again and again. That is where you find peace and freedom.

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A new wave of messages has recently surfaced, claiming that polyvagal theory (PVT) has been scientifically debunked. The trigger is an article by Paul Grossman titled Why the Polyvagal Theory Is Untenable. Despite an adequate response from Stephen Porges, the piece has left a number of therapists and psychologists in doubt. But when you place the criticism alongside the theory itself, a striking pattern emerges: Grossman is once again—and still—largely arguing against a version of PVT that its founder, Stephen Porges, never actually described.

Alongside the work I am doing on several in-depth articles on the subject, I came across a video by Justin Sunseri this week in which he clearly explains several key points. I decided to write a summary about it.

The Vagal Paradox: Two Different Questions

Polyvagal theory begins with a neurological puzzle that Stephen Porges called the vagal paradox. His question was concrete: how can one and the same nerve—the vagus nerve—be both life-protecting and life-threatening? If RSA (respiratory sinus arrhythmia) is understood as a marker of healthy vagal regulation, how do we explain that other vagal responses—such as bradycardia (a slow heart rate) and apnea (cessation of breathing) in premature infants—are associated with life-threatening dysregulation? This paradox formed the basis for Porges’ hypothesis that the vagal system is divided into distinct functional units.

Grossman reformulates this question and turns it into a measurement problem: RSA is simply an imprecise measure of vagal cardiac tone, and that explains the apparent contradiction. But in doing so, he answers a different question than the one Porges was asking. Porges was not asking whether RSA is a reliable measurement instrument. He was asking why the same nerve produces opposing survival outcomes. That is a neurobiological question, not a methodological one.

This distinction matters. The vagal paradox was the driving force behind Porges’ research into the brainstem, which ultimately led to the identification of two anatomically distinct vagal pathways arising from different brainstem nuclei and serving fundamentally different functions. Grossman does not address the vagal paradox in the form Porges posed it, nor does he engage with the anatomical distinction between different vagal circuits that Porges proposed as its explanation.

RSA as a Measurement Tool, Not a Foundation

A large part of Grossman’s article is devoted to the shortcomings of RSA as an index of vagal cardiac tone. If RSA is unreliable, the reasoning seems to go, then the entire theoretical edifice of PVT collapses. But this misrepresents what Porges himself has written about RSA.

In a 2023 publication, Porges explicitly states that RSA is a window onto the function of the ventral vagus—a measurement tool for testing polyvagal-informed hypotheses—but not a foundation of the theory itself. The comparison to a thermometer is illuminating here: if a fever thermometer measures inaccurately under certain conditions, it does not follow that fever as a criterion for infection is untenable. Criticism of the instrument does not touch the underlying reality it is trying to measure.

Grossman cites the relevant 2023 article by Porges. He is therefore aware of it. Why he nonetheless treats RSA as the pivot around which the entire theory turns remains unclear.

Freeze and Shutdown: Two Different States

Another point of criticism concerns the relationship between bradycardia and the freeze response. Grossman argues that bradycardia does not occur during freeze and uses this as an argument against the theory. But in polyvagal theory, freeze and shutdown are described as two distinct states.

Shutdown is a dorsal vagal response: a limp, passive collapse—think of a mouse going limp in a cat’s mouth. Bradycardia fits within this as a physiological response. Freeze, by contrast, is a combined state: immobility resulting from the simultaneous activation of the dorsal vagal system and the sympathetic nervous system. The body is still, but internally under high tension—comparable to a panic attack in which someone freezes. In that combined state of activation, bradycardia is precisely what one would not expect.

So bradycardia does indeed not occur during freeze—exactly as both Grossman and PVT assert.

Admittedly, the terminology around freeze, shutdown, and collapse is not always consistent in the literature; this is an area where confusion regularly arises. Grossman does not make this distinction either, which considerably weakens his argument on this point.

Myelinated Nerves in Non-Mammals

Grossman points to research showing that non-mammals—sharks, fish, and reptiles—also possess fast-acting myelinated nerves capable of directly influencing heart rate. His conclusion: if this anatomy is not exclusive to mammals, it cannot represent a special mammalian innovation for social engagement.

But polyvagal theory never claimed otherwise. Porges has clarified this point repeatedly: the theory is not about whether fast-acting vagal nerves are exclusive to mammals. It is about the evolutionary relocation of the brainstem nucleus from which those nerves originate. In mammals, a so-called ventral shift is described: an evolutionary reorganization of vagal control, in which—alongside the older projections from the nucleus dorsalis motorius (hence the dorsal vagus)—a prominent role emerges for vagal pathways originating in the nucleus ambiguus, located more ventrally in the brainstem (hence the ventral vagus).

This organization is functionally crucial, because the nucleus ambiguus is closely connected to nuclei involved in facial expression, vocalization, and auditory processing. This gives rise to an integrated system in which cardiac regulation and social communication are intertwined. That is the evolutionary claim of PVT—not that fast vagal nerves are uniquely mammalian.

Social Behavior in Reptiles

Grossman notes that modern reptiles display far more complex social behavior than was long assumed: long-term pair bonding, shared parental care, and social learning. As an argument against polyvagal theory, this misses the mark—and Porges has responded accordingly.

PVT is not concerned with the social behavior of modern reptiles as such, but with the specific evolutionary transition from a common extinct ancestor to mammals. Whatever modern reptiles have developed since then follows a separate evolutionary trajectory. To the extent that similarities in social behavior exist, these can be understood as examples of convergent evolution, in which comparable behaviors arise via different underlying biological systems.

Moreover, the theory describes a very specific integration: the coupling of cardiac regulation to facial expression, voice, and hearing, such that social signals—a warm tone of voice, eye contact, a smile—can bring about physiological calming in others (co-regulation). That is something quite different from the social behavior Grossman describes in reptiles.

For Whom Did Grossman Write His Article?

Beyond the substantive objections, something about the article’s design stands out. The abstract and introduction are explicitly directed at therapists and other practitioners who use PVT in their work. The final three of the twelve conclusions address psychology and treatment and encourage care professionals to abandon the theory.

That is remarkable, because the article contains no new arguments against PVT. Grossman is repeating positions he has been publishing for years, to which Porges has responded on multiple occasions. The article presents itself in scientific terms while simultaneously targeting readers who do not systematically follow the primary literature.

That makes it harmful to a fair assessment of PVT: those unfamiliar with the theory’s original formulations have little basis for evaluating the criticism on its merits. The gap between what Grossman argues against and what Porges actually claims only becomes visible when you place theory and critique side by side. The effect is already apparent: therapists and various popular psychology channels have adopted the conclusions without checking whether the criticism described actually corresponds to the theory.

Since this is not the first time Grossman has applied this strategy, it is difficult to characterize it as an innocent mistake.

Work to Be Done

That does not mean Grossman has no valid points. The question of how ventral vagal activity can be measured reliably remains open, even setting aside RSA as a foundation of the theory. The phylogenetic claims—concerning the evolutionary reorganization of vagal circuits in the transition to mammals—are plausible but less robustly supported than the anatomical part of the theory. And the terminology around freeze, shutdown and collapse is not always consistent within the PVT community itself, which complicates comparative research. These are real issues, and they deserve more serious attention than they have so far received.

Conclusion

Scientific criticism is valuable, and polyvagal theory is not immune to questions or refinement. There are legitimate debates about the degree to which RSA is useful as a proxy for ventral vagal activity, about how robust the evolutionary claims are, and about the precise anatomical boundaries of the social engagement system.

But Grossman’s article is largely not about any of that. It argues against a vagal paradox that Porges never formulated, treats RSA as a foundation that Porges himself has explicitly relativized, conflates freeze with shutdown, and misses the evolutionary core of the theory concerning the nucleus ambiguus. When you place the sources side by side, it becomes clear that the heart of the criticism does not connect with the heart of the theory.

Polyvagal theory is not dead. It is the subject of an ongoing scientific debate, and that is precisely where it belongs—only, that debate ought to concern different questions than the ones Grossman is asking.

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In a compelling interview, Dr. Bessel van der Kolk—one of the most influential psychiatrists of our time—shares his insights on trauma and its lasting effects on body, brain, and mind. His work, expressed most powerfully in the bestseller The Body Keeps the Score, has transformed the way the world understands psychological distress and trauma. Rather than viewing trauma as a mental problem, he emphasizes that it is above all a bodily and relational wound—a disruption in the way we experience ourselves and others.

The interview—with the populist title “The Body Trauma Expert: This Eye Movement Trick Can Fix Your Trauma! The Body Keeps the Score!”—runs for two hours. It was well worth watching, and I have written this summary article about it—though it has grown rather long—with a link to the interview at the bottom.

Trauma Is Not a Memory, But a Reliving

One of Van der Kolk’s most striking claims is that trauma does not unfold only in the mind but literally becomes lodged in the body. It is not a bad memory but an experience that is relived over and over again as if it is happening in the here and now. This is visible in brain scans: when people re-experience a traumatic event, the rational part of the brain shuts down while the emotional networks become overactive. The sense of time dissolves. What factually belongs to the past feels as though it is happening now.

This also explains why talking about trauma does not always help. “Trauma is a speechless terror,” says Van der Kolk. “You cannot reason people out of their pain, because in that moment their brain is not functioning rationally.” This makes traditional approaches like cognitive behavioral therapy often insufficient. They focus on ‘correcting’ thought patterns, while trauma disrupts the neurological structures that lie far beneath conscious thought.

The Impact of Early Childhood

In his clinical practice, Van der Kolk sees time and again how devastating childhood trauma can be—and how common it is. Around 90% of his patients struggle with the consequences of a difficult childhood. But trauma need not always have been visible or violent. The deepest scars often arise from neglect, belittlement, or the feeling of being unwanted. Children who are consistently made to feel they are not relevant develop a fundamental sense of unsafety. “You become how you are seen,” he says. “If no one really sees you, you essentially do not exist.”

It is precisely these so-called ‘small-t ’traumas’—critical remarks, subtle rejections, emotional absence—that embed themselves deep within identity. Children often draw the conclusion that something is wrong with themselves because their environment has taught them this implicitly or explicitly. That self-image travels with them into adulthood. So these ‘small-t traumas’ are not so small after all…

The Body as Gateway to Healing

Because trauma affects the body so fundamentally, Van der Kolk has advocated for body-oriented therapies for decades. Qigong, dance, massage, and theatre—these are not alternative whims, he argues, but direct pathways to help the body rediscover itself as a safe place. Many people with trauma have (unconsciously) left their body because feeling was too painful. Recovery begins with daring to be present again in one’s own body.

EMDR

EMDR (Eye Movement Desensitization and Reprocessing) has also proven remarkably effective. By combining the reliving of a trauma with back-and-forth eye movements, the brain is enabled to recognize the experience as ‘past’ rather than ‘present.’ Van der Kolk calls EMDR his “gateway drug” into the world of effective treatments—a first step that taught him trauma can indeed be transformed, provided you work at the right level. In the interview he gives a brief demonstration with the host.

What Happens in the Brain During EMDR?

During an EMDR session, a person consciously brings a traumatic memory to mind, including the images, feelings, sounds, and physical sensations associated with it. At the same time, the eyes follow a rhythmically moving object—often the therapist’s fingers or a light—from left to right. This bilateral stimulation activates brain pathways that are not normally active simultaneously.

Van der Kolk explains that these eye movements likely activate certain networks between the temporoparietal junction (the area where we locate our ‘self’ in time and space) and the insula (the center of bodily awareness). This enables the brain to stop experiencing the memory as ‘present’ and to classify it as something that happened in the past.

“Your brain is able to say, ‘Oh, this is what happened to me, but that happened in the past.”

This is essential: trauma is not a memory but a re-living. In the moment of traumatic activation, the brain makes no distinction between then and now. EMDR appears to help restore this distinction by literally moving the brain across the midline—from left to right hemisphere.

Van der Kolk’s own research confirmed the effectiveness: in 78% of adults with single-incident trauma (such as assault or a car accident), EMDR led to complete symptom relief. Complex childhood traumas are more stubborn, but even there EMDR can be a powerful tool, provided it is embedded within a broader, safe therapeutic relationship.

The Body Knows the Way to Healing

That the body and movement are central to trauma recovery became even clearer to Van der Kolk during a visit to China in the 1990s. The country was just emerging from the Cultural Revolution—a period of suppression, violence, and collective silence. In conversations with residents, he was struck by how little people openly spoke about what had happened. Regarding the Tiananmen protest, for example, people simply said, “That never happened.”

And yet he saw something different in the public parks: hundreds of people practicing Tai Chi and qigong together each morning. Slow, flowing movements. Body and breath in a rhythm. No words. No explanations. But something is working deeply on the nervous system.

For Van der Kolk, this was a revelation. “This is how they survive,” he thought. Where the West focuses on talking, analyzing, and taking medication, he discovered a different gateway to recovery: regulation through rhythm, movement, and synchronization. Not through the head, but through the body. Not alone, but together.

It set him thinking about how different cultures cope with pain and dysregulation. In the West, we invest in ‘understanding’—in ’talking about trauma. But what if you have no words for it? What if language disappears, as it does for so many people with deep trauma? Then the body—in movement, in repetition, in rhythm—can open a new path.

Since then he has argued ever more explicitly for recovery through physical processes. Not as a replacement for, but in collaboration with, more conventional approaches. Whether yoga, qigong, dance, breathwork, or martial arts, the path to yourself runs through your body. And often through another person as well.

How Trauma Changes Perception Itself

During his work with traumatized war veterans, Van der Kolk began to explore how trauma affects not only feelings and behavior but literally alters the way people perceive reality. One of the most revealing discoveries came through the use of the classic Rorschach test—the well-known inkblots that invite people to describe what they see.

What Van der Kolk and his team discovered was that traumatized people consistently saw different images than non-traumatized individuals. Where some recognized abstract shapes or animals, war veterans saw blood, mutilated bodies, or violence. Women with a history of sexual abuse saw torn bodies or threatening figures. What was identical on paper was interpreted in entirely different ways internally.

These observations confirmed something Van der Kolk had long suspected: we do not all live in the same reality. Trauma essentially programs a different ‘filter’ into the brain—a lens through which the world is constantly scanned for danger, loss, or betrayal. Even when nothing appears to be wrong, the body remains in a heightened state of readiness. “We all live in different worlds,” he says, “shaped by what we have previously experienced, often without our awareness.”

This insight has far-reaching implications for therapy. It means that healing begins not with persuasion, but with restructuring the sensory and emotional foundations of a person’s reality. Only when the body learns it is safe can the brain begin to rewrite its story.

What Trauma Does to the Brain

Van der Kolk’s work is distinguished in part by its focus on the neurobiological traces of trauma. Using brain scans, he demonstrates that traumatic memories are not merely ‘stories we recall’ but deeply ingrained physical responses in specific brain regions. When someone relives a traumatic experience, the brain responds in a characteristic way.

It begins at the most primitive core: the periaqueductal gray, deep in the brainstem—what Van der Kolk calls the “cockroach center” of our brain. This area, once danger is perceived, directly activates the body in a reflexive fight, flight, or freeze response. In people with trauma, this alarm continues to sound faintly, even without direct cause. The result is a constant state of tense vigilance, as if something is always threatening1.

Above this sits the amygdala, the brain’s ‘smoke detector.’ At traumatic triggers—a smell, a sound, a glance—this area reacts with lightning speed. It recognizes threat patterns based on past experience, often before the rest of the brain has time to think logically. In traumatized people the amygdala is frequently overactive, causing even harmless situations to feel threatening.

At the same time, the prefrontal cortex—the rational brain—is deactivated. This region, particularly the dorsolateral prefrontal cortex, is responsible for overview, sense of time, self-reflection, and the ability to contextualize. When this area ‘goes offline,’ the awareness that something belongs to the past disappears. What remains is the immediate, overwhelming experience as if the trauma is happening again right now.

Another crucial player is the insula, the brain region that links body and feeling. It is through the insula that we feel what we feel: heartbeat, tension, breathing, and goosebumps. In people with trauma, this connection is often disrupted. Some can barely feel their body at all—as if it has been ‘switched off’—while others are hypersensitive to every internal sensation. In both cases the relationship with one’s own body is fundamentally dysregulated.

What all this makes clear is that trauma is not a psychological weakness but a state of being—above all, a state of the brain. You are not ‘emotionally unstable’ or ‘oversensitive’—your brain has adapted to unsafety. And that also points the direction for recovery: if the brain has adapted, it can also learn to attune itself again—provided you find the right entry points and involve the body.

Psychedelics: A New Revolution

Recently Van der Kolk has also turned his attention to psychedelic therapy, including treatments with MDMA, ketamine, and psilocybin. The results from clinical studies are astonishing: people with chronic PTSD, who had previously derived no benefit from conventional therapies over many years, experience profound breakthroughs. Not only do symptoms diminish, but people rediscover compassion for themselves, feel reconnected with their body and surroundings, and can finally recognize the past as past.

Van der Kolk himself underwent an MDMA session as part of his research. To his own surprise, not pleasure or euphoria arose, but deep grief—a confrontation with the thousands of traumas he had heard as a clinician over the years. “I became a sadder but also wiser person,” he says. This underscores for him how essential the right setting is: safety, guidance, and human presence make the difference between healing and retraumatization.

Healing Requires Community

At least as important as therapy is connection with others. According to Van der Kolk, isolation is one of the most destructive factors in trauma-related conditions. People heal in relationships—through shared experiences, rhythm, and synchronicity. Sport, theatre, music, and dance: these are, in his view, age-old forms of collective regulation that are at risk of disappearing in our modern, digital society. Yet it is precisely there that recovery begins.

He describes how young people in criminal gangs often seek precisely that sense of belonging—the “band of brothers” they never had at home. Or how soldiers, through marching, singing, and training together, restructure themselves into a functioning unit. It is not the talking that heals them, but moving together, existing together.

Attachment: You Become Who Sees You

According to Van der Kolk, psychological well-being does not begin with reason or behavior, but with relationship—from the very first moments of life. He emphasizes that secure attachment to a caring parent or caregiver literally forms the blueprint for how a child experiences itself, others, and the world.

“You become how people see you,” he says. That sounds simple, but the implication is profound. When a child is consistently seen as valuable, loved, and welcome, it grows up with the sense that it is worthwhile. But when it encounters unpredictability, emotional distance, or rejection, that experience becomes a fundamental part of the personality. “If no one truly sees you, you essentially do not exist.”

He gives the example that children do not consciously ask themselves whether they are safe—they become safety, or they become fear. When a mother says, “You are too difficult; that’s why your father started drinking,” that is not merely a hurtful remark but a message that becomes lodged in body and self-image. Subtler forms of misrecognition—a parent who persistently tells the child it is ‘overreacting’ or ‘shouldn’t feel that ’way’—can also have deep consequences. The child then learns not to understand itself but to distrust itself.

Secure attachment does not mean parents are perfect. It means, above all, that there is consistency, availability, affection, and repair when something goes wrong. That a child knows, “When I am frightened, someone comes. When I fall, I am picked up. When I am confused, I am not shamed but understood.” That is the soil in which resilience grows.

Van der Kolk draws an important social conclusion from this. In a culture where parents often stand alone, where childcare and schools are under pressure, and where connection is giving way to screen time, children sometimes lose the mirroring that helps them construct a sense of self. Attachment is not a luxury, he argues, but a neurobiological necessity.

And just as with trauma, so too here: it is never too late to restore connection. People can still learn to experience themselves—and others—as safe. But it requires attention, a body, and a relationship.

From Burden to Baggage

Van der Kolk also points to an important paradox: although early wounds can leave deep scars, they can also become a source of strength. Those who have had to survive at a young age sometimes develop their own ways of overcoming obstacles. “It is often the people who have had to endure something,” he says, “who later come up with solutions others would never even consider.” Early struggle can kindle creativity and problem-solving capacity—not despite, but precisely because of the necessity to adapt.

Yet this is not available to everyone. Much depends on the environment, the possibilities for recovery, and the support network that happens to be present. For every success story of a ‘resilient survivor,’ there are countless others who have become quietly stuck. Van der Kolk therefore emphasizes that we must be careful about labeling trauma too positively: it can shape people but also break them—and usually does both at once.

How Do You Avoid Traumatizing Your Children?

On the question of how parents can protect their children from trauma, Van der Kolk is clear: make sure you do not do it alone. Children are not only harmed by abuse or mistreatment but also by emotional isolation, unpredictability, and the lack of safe co-regulation. And parents—however well-intentioned—inevitably carry their pain and patterns with them. Parents raising children alone, therefore, risk burdening their child with their own unconscious wounds simply because there is no other perspective in the household.

His advice is therefore radically simple: build a network. Ensure your child has multiple adults around them who are available, calm, and engaged—so that the child learns that safety is not accidental but reproducible. That father is sometimes strict, but grandmother is gentle. That the neighbor is patient when mother is stressed. In this way a child learns: my world is larger than one person’s mood. And I am safe, even when someone else temporarily is not.

Ultimately, says Van der Kolk, raising a non-traumatized child is not about doing everything perfectly but about being present, predictable, and attuned. And about letting the child feel: if you are overwhelmed, someone will come who stays.

Van der Kolk shares a particularly personal moment that moves him to this day. During a visit from his parents, his three-year-old daughter asserted herself at home in the way that is perfectly natural for a toddler. His mother reacted with irritation and said he should discipline her. He immediately felt that reflex rise—the impulse to intervene, to correct her, to repeat the patterns of his childhood. He had even risen to walk towards his daughter when suddenly the realization struck him: “I am about to become like my parents were.”

At that moment he consciously chose differently. He turned to his mother and said, “No, she can go to the bathroom.” For him this was a liberating moment—not only a choice in favor of his daughter but also a release from unconscious loyalty to his parents. It was, as he says, the first time he truly felt ownership of his parenthood and of himself.

Yet he also calls this a painful moment. Because breaking patterns often means leaving one’s ‘tribe’—the group one belonged to, even if it caused harm. “We want to belong somewhere,” he says, “that is deeply human. But when you truly change, you leave something behind. And that can be lonely.” It is a theme he frequently sees in patients: the desire for healing often collides with the implicit fear of being cast out. “You leave your tribe,” he says. “And then you must learn to find a new one.”

In therapy—or in parenting—it is therefore not only about healing but also about choosing: who do I want to be when I am no longer driven by fear, guilt, or old reflexes?

Both Agitated and Numb

One of the most confusing and exhausting consequences of trauma is what Van der Kolk describes as “being agitated and numbed out at the same time.” You feel driven, irritable, and alert—as if something is constantly wrong—and at the same time you are inwardly numb, empty, or shut down. Your body is taut with tension, but you feel nothing that provides direction. Van der Kolk calls this a characteristic state in people with a traumatized nervous system: the body is in a state of threat, while the feeling system has partially shut itself down to avoid being flooded. You can barely tolerate anything, yet at the same time you feel dull and far removed from yourself.

That paradoxical field of tension—hypersensitivity and numbness in one—makes life unpredictable and difficult to navigate. You do not know whether you are going to explode or collapse. It also makes it so difficult for the outside world to understand what is going on: you appear ‘flat’ or ‘disinterested,’ while inwardly you are flooded. Van der Kolk emphasizes that this state is not a character flaw but a neurological defense strategy of the body. And that from it—slowly, through safety, rhythm, and body work—one can emerge.

Mirror Neurons and Co-Regulation: How We Influence Each Other’s Nervous Systems

During the conversation, Van der Kolk points to the existence of mirror neurons—brain cells that become active when we see someone else do, feel, or undergo something. These neurons cause us to resonate with the other person, even when we ourselves are doing nothing. They form the neurological basis for empathy, attunement, and intuitive understanding. “We pick up each other’s energy,” says Van der Kolk, “often without noticing.”

This aligns seamlessly with the polyvagal theory of professor of psychiatry and neuroscientist Stephen Porges, in which the concept of co-regulation is central. According to this theory, our autonomic nervous system is not only attuned to internal signals (such as breathing or heart rate) but is constantly scanning the environment for social signals: voice intonation, facial expression, rhythm, and proximity. When we feel safe with another person—because their voice is calm, their face soft, and their breathing quiet—our own nervous system calms in turn.

In other words, we regulate each other. Not through words, but through eye contact, body language, voice, and rhythm. Van der Kolk and Porges describe, each in their own way, the same thing: that trauma is not a purely individual problem and that recovery rarely takes place in isolation. You cannot ‘talk yourself out of hyperarousal,’ but another person can—by being present, attuned, and safe—help your system to come to rest.

This is why Van der Kolk advocates for therapeutic approaches in which not only talking occurs, but where rhythm, proximity, and bodily attunement also have a place: from psychodrama to dance, from qigong or yoga to shared breathing. The body only learns to feel safe in the proximity of another body that radiates safety.

What Screens Take From Us

Precisely in light of these deeply relational processes, Van der Kolk is concerned about the advance of screen culture. Instead of bodily proximity, shared rhythms, and sensory attunement, we are spending ever more time in virtual worlds. Screens provide information, but not regulation. They offer stimulation, but not safety. “You get a small dopamine spike,” he says, “but you do not learn how to truly connect—with yourself or with others.”

The result is a society in which people increasingly live alone, fragmented, and disconnected from their bodies. Even young children grow up with less physical touch, fewer live facial expressions, and fewer shared rituals. In doing so they lose something fundamental: the capacity to attune their inner world to another. And that, warns Van der Kolk, makes us more vulnerable than ever to dysregulation, stress, and loneliness2.

Love as a Neurological Experience

For Van der Kolk, love is not a poetic side note to life—it clearly has a neurological foundation. “Love,” he says, “does not reside only in words, but in glances, touches, rhythms—in the subtle coordination of two nervous systems learning to trust each other. Someone says, I am here for you. And your body believes it.”

In his work with war veterans, he saw how deep, life-saving bonds can form under the most terrible circumstances. “Combat taught me more about male love than anything else,” he says. Real love arises where people protect, mirror, and carry one another—especially when it is difficult. Not the absence of danger makes love possible, but the experience that someone stays with you when you are afraid.

This is why healing is never a purely individual journey. We are wounded in relation to others—and we heal in relation too. Whoever is seen lovingly, touched, or held can gradually learn that the world may not, after all, be only unsafe. And that the body—in which the pain had lodged itself so tenaciously—can also become a place of homecoming.

The Culture of Loneliness

Beneath everything Van der Kolk says—about brains, attachment, rhythm, love, and recovery—lies a simmering warning: we live in a world that is slowly unraveling us from one another. A world in which screens replace faces, voices are filtered through earbuds, and physical proximity is increasingly experienced as uncomfortable. “The average American,” he cites, “now has zero people they can turn to in a crisis. Twenty years ago that number was three.”

It is as if society is being increasingly organized around autonomy, self-reliance, and productivity—but not around connection. And so we become ever more efficient, but also ever lonelier. We seek safety in information, distraction in pixels, and recognition in algorithms—but our bodies continue to long for something else: rhythm, touch, proximity, and togetherness.

Three Steps Toward Healing According to Bessel van der Kolk

Rather than beginning with a diagnosis or problem description, Van der Kolk starts his treatments with a simple but deeply personal question: “Tell me who you are.”

This question forms the beginning of a three-part approach he sketches in the interview3:

1. Self-inquiry: Who are you? What works? What blocks? Therapy begins with curiosity, not labels. Van der Kolk wants to know who someone is, what gives them energy, what gets stuck, what has helped before, and what has not. Not “How ill are you?” but “What does your inner world look like?” This first phase revolves around meaning-making, self-knowledge, and building a respectful therapeutic relationship.

2. Bodily regulation: first calm the nervous system. Only when the body feels safe is there space for processing. Many people with trauma are constantly flooded or numbed, or both at once. Van der Kolk uses techniques such as yoga, neurofeedback, breathwork, massage, or EMDR to help stabilize the nervous system. “If you are overwhelmed, don’t start with talking,” he says, “but with moving, feeling, and regulating.”

3. Processing the core experience: gently touching the trauma. Only once sufficient safety is established is the core experience itself approached. This can occur through EMDR, psychedelic therapy, psychodrama, or other experiential methods. The memory is relived, but this time from the here and now, in a controlled, guided context in which the brain learns to feel the difference between then and now. Central is not digging in the past but reprogramming the senses and the nervous system.
   
   “That was then. And now it is safe.”

Trauma Is Never One Story

Gabor Maté, another prominent voice in the trauma field, argues that ADHD, addiction, and many forms of psychological suffering can very often be traced back to early childhood trauma or stress. Van der Kolk recognizes himself partly in this view but also emphasizes that reality is more complex. Not everything is trauma—and not everyone develops difficulties from the same origin.

“Almost all traumatized children meet the criteria for ADHD,” he says, “but that does not mean everyone with ADHD necessarily has a trauma.” He points to multiple causes: genetics, neurodiversity, environmental factors, and toxins during pregnancy—all can contribute. Psychological symptoms are, in his view, often the tip of the iceberg; what lies beneath varies from person to person.

The nuance he introduces is essential: it is not about imposing trauma as the explanation but about remaining curious with each person about the story beneath the symptoms—whether that is trauma, temperament, or chance. Healing does not begin with a label, but with listening.

A System That Falls Short

Van der Kolk makes no bones about it: the current psychiatric diagnostic system—as codified in the DSM (Diagnostic and Statistical Manual of Mental Disorders)—falls seriously short. “It totally sucks,” he says bluntly. Not because psychological distress is not real, but because the system categorizes symptoms without looking at the context from which they arise. Whether someone is anxious, withdrawn, aggressive, or addicted—the DSM does not ask, “What happened to you?”

According to Van der Kolk, this leads to treatments that focus on managing behavior rather than understanding causes. And this suits a society more interested in productivity than in healing. Instead of helping people recover, their suffering is medically translated into ‘disorders’—often ’with an accompanying prescription, but without genuine contact.

“The focus is not on healing, but on keeping the system running.”

What he proposes is no simple alternative, but a radically different approach: listening, slowing down, and looking at the whole story—body, brain, relationships, and history. Not: What is wrong with you? But what happened to you?

No Scientific Foundation

According to Van der Kolk, most psychiatric diagnoses are not based on hard science but on consensus agreements between experts—often reached in meeting rooms, not in laboratories. There is little to no biological grounding, and most categories are superficial descriptions of behavior, not of causes.

“They’re just very primitive ways of categorizing the human mind.”

An exception, in his view, is PTSD (post-traumatic stress disorder), which does have brain scans, neurobiological patterns, and clinical research as its foundation. Not coincidentally, Van der Kolk himself was involved in introducing PTSD into the DSM in the 1980s. But even there he sees limitations: PTSD focuses primarily on single-incident trauma (such as accidents or violence), while early childhood, relational trauma—which leaves deep traces in the brain and in attachment patterns—is barely recognized within official diagnostics.

In short, the system gives names but no insight. It describes symptoms but does not ask about the origin. For Van der Kolk, this is unacceptable. Psychological pain deserves more than a label—it deserves a context, a story, a human being.

A Message of Hope

Despite the weight of the subject, Van der Kolk is emphatically hopeful. “Everything that has been disrupted can be set in motion again.” Trauma is persistent, yes—but not unchangeable. The key lies in taking bodily and relational processes seriously, in daring to experiment with new forms of therapy, and in cherishing genuine connection.

His message is clear: we must stop treating people as symptoms and learn again to listen to their story—with heart, mind, and body.

That movement is not a straight line. It requires time, attention, and proximity—and sometimes new forms of therapy that do not proceed only through language but through touch, rhythm, breath, and space. And above all, it requires something that costs nothing but has become rare: genuine presence. People who stay. People who look without judgment. People who say, I see you. I am not going anywhere; I will stay with you.

Based on the interview with Dr. Bessel van der Kolk, The Diary of a CEO, March 2025.

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Recently I have become increasingly aware of the possible effects of word choice and language use. Partly through my interest in how journalism shapes the way we experience the news. But also because years of working as a mindfulness and resilience trainer have taught me a great deal about the impact of language on what someone learns—or what insight arises—during a training day. And writing articles, which I have been practicing for some years now, has been its own teacher.

Even so, one of the most formative experiences of the past few years was an article I read about how perpetrators and victims are ‘handled’ in news reporting—and how this has a profound effect on the way society treats victims.

When I recently watched a TED talk about how the language you speak influences how you describe a bridge, I decided the time had come for an article about language and grammar. So here we go.

Guilt or Accident

Imagine you witness an…

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This article is part of “The Polyvagal World” on RelaxMore.net and is intended as an accessible starting point for anyone who is new to polyvagal theory. Additional articles on RelaxMore.net and in the Relaxicon explore specific themes such as neuroception, co-regulation, and fawning in greater depth. Questions are welcome in the comments.

Introduction

Polyvagal theory is about the communication between the brain and the body. It describes how internal and external signals—largely outside our conscious awareness—influence our sense of safety and guide our behavior. The theory offers insight into the intelligence of our evolutionary heritage: over millions of years, that heritage has shaped our nervous system with one purpose in mind: to protect us and enable us to function optimally within our environment.

The theory touches on several disciplines at once: psychology, physiology, evolutionary biology, and neurology. This synthesis sometimes complicates it, but also especially valuable—it connects what mainstream medicine still too often treats in isolation.

Are you a therapist or healthcare provider interested in this material?

I have developed a two-day training program (in Dutch): “Polyvagal Theory and Trauma Responses” — in-depth theory with practical application.

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The Science of the Feeling of Connection and Safety

It is remarkable that William James already sensed in 1914 how decisive our nervous system is for our well-being. Exactly eighty years later, Stephen Porges gave this scientific grounding in polyvagal theory. Safety—or rather, the inner experience of safety—plays a central role:

What Is Polyvagal Theory About?

The autonomic nervous system—the part that unconsciously regulates all kinds of bodily functions—turns out to be more than just a control system for our physiology. It also contains the core structures that allow us to experience safety or threat. Polyvagal theory describes what one might call the language of our autonomic nervous system.

Professor of psychiatry and neuroscientist Stephen Porges published the theory in 1994. He shows how the evolution of our autonomic nervous system explains why we respond to stress, threat, and social contact the way we do. In doing so, he draws connections between autonomic dysregulation and a broad range of physical and mental complaints.

Polyvagal theory is increasingly concerned with connection and love: with the factors that make connection possible, and with what happens when that connection is absent. In this way, it also offers guidance for broader social questions: how do we make the world a safer place?

Polyvagal theory is about how our body responds to the various challenges of life. These responses are rooted in the evolution of our autonomic nervous system. Throughout our evolutionary history as vertebrates, that autonomic nervous system has gradually changed. In the process, new pathways or circuits have emerged. These circuits function in a hierarchy; the newer circuits inhibit the older ones. Those older circuits are the defense or protection circuits. In medicine and various therapies, we are now gaining greater insight into the role that a dysregulated autonomic nervous system plays in many diseases, especially chronic ones. The autonomic nervous system also exerts a significant influence on mental health.

A poorly regulated autonomic nervous system—in other words, one that is dysregulated, or out of balance—may, according to polyvagal theory (PVT), help explain several gastrointestinal complaints (including constipation, irritable bowel syndrome, and spastic colon), most post-traumatic symptoms, sensory hypersensitivity, and some features associated with autistic traits.

What is particularly valuable about Porges’ work is that he not only developed a theory but also foresaw its practical implications. He proposes alternative, more body-oriented treatment options, which have already produced good results. Recently, Porges has devoted increasing attention in his work to the practical implications of polyvagal theory.

Polyvagal theory is increasingly about love and connection. The theory sheds light on the factors that make connection possible, but also on the factors that play a role when we miss or lose connection. Through this new science, we can learn what in our society will help make the world a more loving place.

What Does ‘Polyvagal’ Mean?

Poly means ‘multiple’; vagal refers to the vagus nerve, one of the most important cranial nerves in our body. Polyvagal therefore, means ‘multiple vagal pathways.’ The impression may arise that the theory is only about the vagus nerve, but that is not the case. Four other cranial nerves also play a role, and the theory describes the entire autonomic nervous system as an integrated whole.

How Does Polyvagal Theory Stand Scientifically?

Polyvagal theory has found broad acceptance in clinical practice—in trauma care, body-oriented therapy, and developmental psychology. Pioneers such as Peter Levine (Somatic Experiencing®), Bessel van der Kolk, and Pat Ogden recognized in Porges’ work the neurobiological explanation they had been searching for—the one that confirmed what they had been observing in the treatment room for years: the path to trauma healing runs through the body.

At the same time, there is scientific debate. The most prominent criticism comes from researchers Grossman and Taylor, who raised questions about a number of anatomical and evolutionary details of the theory—particularly regarding the interpretation of the vagus nerve and the evolutionary ordering of vagal circuits. Porges has responded to this criticism and refined parts of his formulation. That debate is not fully closed, and rightly so: this is how science works.

The core of polyvagal theory—that our autonomic nervous system operates within a hierarchy of survival circuits and that safety is the foundation for connection and recovery—stands firm as a clinical explanatory model and continues to be substantiated. Elsewhere on this website I discuss the scientific debate in greater depth; the website of the Polyvagal Institute (and here the Dutch foundation) is also worth following in this context.

The Three Pillars of Polyvagal Theory

Polyvagal theory rests on three interconnected insights. In most accounts, these pillars are listed in the same order: (1) Autonomic Hierarchy, (2) Neuroception, and (3) Co-regulation.

The first pillar receives the most attention in the literature, but that is not, in my view, a reason to describe it first in this overview. I now prefer a ‘chronological sequence’: what happens, step by step, in real life? That gives a different order:

1. Neuroception (the scanning process that sets everything in motion), and then, on the basis of that scanning, the regulation of the…

2. Autonomic hierarchy.

3. Co-regulation comes third, though it remains a somewhat tricky concept wherever you place it.

Ordinarily, a paywall would appear here — but because I consider this an important article for anyone with an interest in polyvagal theory, I have removed the paywall for this article.

Pillar 1: Neuroception — Our Unconscious Safety Radar

Our nervous system continuously scans the environment, our body, and the relational field for signals of safety or threat. This happens at lightning speed, automatically, and entirely outside our conscious awareness. Porges calls this process neuroception: the neural detection of safety, danger, or life threat.

Neuroception differs from perception. Perception is conscious awareness; neuroception is a deeper, older system that responds before the cerebral cortex has processed the information. This explains why we sometimes feel tense in a situation that ‘objectively’ seems safe or why we relax while others remain worried: our neuroception is responding to subtle signals we do not consciously notice.

The Three Information Channels of Neuroception

Neuroception draws on three streams of information to determine whether the current place and moment are safe or whether there is danger or life threat:

• External signals: environmental sounds, light intensity, spatial openness or enclosure, the familiarity of a place, and all other information coming in through the senses.

• Internal signals: muscle tension, heart rate, breathing, gut feelings, pain, fatigue, nausea, temperature sensation, hunger, thirst—in short, everything that arrives via interoception (the ‘inner senses’).

In people with a chronic condition, this channel is especially relevant and often especially problematic: the body continuously sends signals of unsafety or threat—pain, exhaustion, discomfort—causing neuroception to be structurally colored toward danger, even when no external threat is present. This explains why chronic pain and fatigue are so closely intertwined with autonomic dysregulation.

• Relational signals: these are signals that come directly from the nervous system of another person—tone and quality of voice, facial expression and eye contact, body posture and movement, and the quality of touch. It is not the environment or context as such, but what the other body radiates and what our nervous system picks up from it, before we do anything consciously with it.

Based on this scanning process—which takes place around the clock, using ancient brain structures in the brainstem and surrounding subcortical areas to analyze the incoming information from all three streams — the nervous system determines which autonomic state (Pillar 2) is appropriate, and automatically ‘switches’ to it. We do not choose this; our body does it for us.

Where our consciousness enters the picture is when we notice that our autonomic state has changed—for example, that our heart rate has gone up or that we feel more or less tense.

When Neuroception Makes ‘Mistakes’

We are all generally born with a reasonably well-calibrated neuroception. Our neuroception is ‘trained’ by the experiences we go through and can become dysregulated in the process. In people with a trauma history, neuroception may detect danger where none exists, or miss genuine threat signals. A relatively neutral remark from a colleague is experienced as an attack; a crowded room triggers panic; intimate contact feels unsafe. This is not a conscious choice or ‘overreacting’; it is a nervous system that has learned to be extra vigilant.

In people who experienced severe stress very early in life—for example, a premature birth, medical interventions as a newborn, or even significant stress in the womb — neuroception may be calibrated toward threat from very early on. In my articles on GHIA, I write more about this.

These insights have major consequences for how we relate to people who react strongly to situations that seem neutral to us. The question should not be ‘Why is he or she making such a fuss?’ but rather ‘What is this person’s nervous system detecting that mine is not?’ or perhaps even better, ‘What have you been through?’

Our neuroception does not make mistakes; it has been calibrated based on our experiences. Its intention has always been, and still is, to help us survive in a way that costs as little energy as possible.

Pillar 2: The Evolutionarily Shaped Autonomic Hierarchy

Now that we understand how the nervous system scans the environment (neuroception) — and how this forms the basis for regulating autonomic state—let us look at what the available options actually are.

Polyvagal theory describes that we humans share the same survival strategies as other mammals. When we feel safe, we are more inclined to seek connection with one another. This happens via the so-called ventral vagal circuits. One might also call this the ‘connection system’. In this state, we are able to feel compassion, comfort others, and behave in a friendly and understanding way. We feel more caringly connected to ourselves, and we are able to learn.

When neuroception detects a threat, a number of responses become available. These are often presented as a predictable, stepwise sequence of responses. Reality is somewhat less linear, but for now we will use the standard sequence.

First, we try to resolve a threatening situation by establishing a social connection. We ask for help or offer to help. The connection system is further activated. If this does not lead to a restoration of safety and connectedness, we then automatically engage our sympathetic nervous system (the action system) to flee from or fight against the source of threat. Fight and flight sometimes occur literally, but today more often figuratively—for example, raising one’s voice or blaming others (fight) or changing the subject or acting very busy (flight).

If activating the action system does not produce the desired effect, we ultimately fall back on the dorsal vagal circuits (let us call this the rest-and-withdrawal system), which immobilizes us in a freeze response. In this state, we feel helpless, powerless, and shut down.

Polyvagal theory thus describes three levels for dealing with stress and threat: three hierarchically organized subsystems of the autonomic nervous system.

The confusion often lies in the word hierarchical. The hierarchy is not so much about which state is activated after which; rather, it refers to evolutionary age and the fact that ‘newer’ systems inhibit the ‘older’ ones. In evolutionary terms, the rest-and-withdrawal system is the oldest, followed by the action system, with the connection system being the most recent.

We use our higher, newer brain structures to inhibit our older defense systems when there is no danger. An evolutionarily determined hierarchy—or, in more formal language, a phylogenetic ordering (i.e., the developmental history of a species).

Summary

For clarity, the following sequence is useful:

• In safety, or when safety is in question: seeking contact and social connection via the connection system. If that is not sufficient…

• When there is danger or apparent danger, switching to mobilization—the action system activates via the fight-and-flight response. If that also fails…

• Then there is apparently a life threat: a response of immobilization or freezing arises via the rest-and-withdrawal system.

This sequence suggests too rigid an order; for sensitive readers, a value judgment may also seem implicit—as if having the connection system activated is somehow better than having one of the other two active. The sequence fits with the concept of an autonomic ladder, an image widely used to explain polyvagal theory and one that has been very helpful but for which we now have better alternatives.

As we already concluded in the section on neuroception, the goal of the whole process is to ensure our survival. There are therefore no ‘wrong’ autonomic states; they are all adaptive—a response to the situation as neuroception has interpreted it.

Not Only in the Face of Threat

These systems do not only activate in response to stress and threat; they are also active in daily life. Our autonomic nervous system is always ‘on,’ 24 hours a day. Even when we experience no threat, the three systems are active in some combination. When exercising, the action system is active—but without threat being present; when meditating, the rest-and-withdrawal system comes to the foreground—again, without threat. This is an important addition that polyvagal theory has contributed.

Mixed States

Another aspect of autonomic regulation is that the three systems do not switch on and off like light switches but shift gradually. For this reason I have moved away from the ladder metaphor and developed an autonomic mixing panel.

This yields an even more nuanced picture of how the three systems work together and allows us to name states in which two systems are simultaneously in the foreground. When you are sitting with your partner on the sofa, for example, the chances are that both your connection system and your rest-and-withdrawal system are active. Often during exercise, not only the action system is running, but the connection system is also engaged. There are countless examples of how the autonomic mixing panel might be set at any given moment.

In recent years, considerable attention has also been paid to the concepts of fawning and please-and-appease—both of which are also examples of mixed states.

In this picture, neuroception is the hand that operates the mixing panel:

Free Choice?

No one consciously chooses to enter a fight-or-flight response or to freeze. Many survivors of violence or abuse carry feelings of guilt about not having resisted or having resisted less than they feel they should have. The response to life-threatening events, however, is not a voluntary choice; our body makes that choice based on neuroception.

In polyvagal theory, there is no such thing as a bad response—there are only adaptive survival responses.

No Fixed Sequence

Which autonomic state is activated in a given situation—whether safe or threatening—and how it is expressed differs from person to person. The evolutionary hierarchy is fixed; the three systems have developed in the sequence described. But the hierarchy does not mean that you always move from the connection system to the action system; this ‘phase’ can be skipped entirely, and someone may shift directly into the rest-and-withdrawal system.

Earlier experiences can cause the connection system to be less developed or to become depleted quickly, so that even a mild threat leads someone to slide into action or withdrawal. A very severe situation may also mean that the connection system is not further activated; after all, there is no point in seeking help when your house is on fire—you need to run (action system → flight).

Structures Involved

Central to all of this is the evolution of several cranial nerves, with the vagus nerve playing the most prominent role. You can read a great deal about this same vagus nerve these days on so-called social platforms. In addition to the vagus, four other cranial nerves play a role in the polyvagal story. And from there, the whole body, the entire hormonal system, and the entire metabolism are involved.

Pillar 3: Co-Regulation—Regulating Together

Our nervous system is not a solo performer. As mammals, we are naturally oriented toward connection with others, and that connection has a direct physiological effect. The presence of a calm, safe other person literally calms our nervous system—and when we are in a calm state ourselves, we can help others calm down too. This is what we call co-regulation: the mutual influence of nervous systems on one another.

How Does Co-Regulation Work?

The ventral vagal circuit (the connection system)—the evolutionarily newest and most developed part of our autonomic nervous system—is neurally connected to the muscles of the face, voice, and head. This connection enables social communication: a soft voice, an open facial expression, gentle eye contact. Through these channels, our nervous system constantly ‘reads’ the state of the other person’s nervous system.

A calm therapist, an attentive parent, a settled friend—their regulated nervous system functions as an external regulator for ours. This is not a metaphor or poetry. It is neurobiology.

Co-Regulation in Practice

The concept of co-regulation is helpful in explaining how and why young children develop their nervous system in the context of a caregiver and why early attachment is so important.

We also know that the therapeutic relationship can itself be healing, independent of the method the therapist uses; in this sense, the therapist ‘does’ something simply by being present. Most people have experienced, at some point, how someone in crisis can be calmed simply by being fully present—and conversely, how someone in panic is not helped by a loved one who also falls into panic. In groups, the dynamic can be powerful in both directions: co-regulating as well as destabilizing.

To make optimal use of co-regulation, it is important that professionals themselves have a well-regulated autonomic nervous system and can remain regulated even when their client is not.

Co-regulation is listed here as the third pillar, but you may well understand by now that its effect becomes visible through neuroception in an autonomic state. Co-regulation could therefore also be placed first in the sequence! Polyvagal theory is describing a genuinely dynamic system.

Self-Regulation as a Complement

If you learned to co-regulate well as a child, the capacity for self-regulation develops. Techniques such as mindfulness, breathing exercises, Tai Chi, and Qigong help calm the nervous system from within.

Why Is Polyvagal Theory Important?

The theory does not only offer an explanation for what happens in the nervous system—it also has direct implications for how we relate to people, to complaints, and to recovery.

Education and Child-Rearing

A safe environment is not a luxury; it is the physiological prerequisite for learning and development. A nervous system operating in defense mode—with the connection system less active—cannot learn optimally. Children who grow up in unsafety develop a nervous system that is constantly on alert. The consequences are measurable well into adulthood, as extensively demonstrated by research into Adverse Childhood Experiences (ACE).

For the (Psycho)Therapeutic Practice

Polyvagal theory shifts the therapeutic gaze from ‘What is wrong with this person?’ to ‘What survival response has this nervous system learned?’ That is an important and less stigmatizing perspective. Body-oriented therapies such as Somatic Experiencing® work directly with autonomic state, far less through talking and cognitive processing.

For the Professional Themselves

Co-regulation makes clear that a professional does not only apply techniques, but is present with their own nervous system. A regulated professional offers a regulated space. This may well be the most active ingredient of any therapy or coaching session. As Stephen Porges said:

For Medication and Treatment Choices

Insight into autonomic dysregulation helps explain why certain treatment methods work and others do not. It also offers entry points for new interventions—from HRV biofeedback to voice use, from group therapy to body work.

For Society

At the societal level, polyvagal theory asks: which environments create safety, and which create chronic threat? This touches on architecture, policy, healthcare, and education — everywhere that people live and work together.

For each of these points, articles will be appearing on this website in the coming period—stay tuned!

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Implications of Polyvagal Theory

When Porges published polyvagal theory in 1994, he did not yet anticipate that pioneers such as Peter Levine (founder of the body-oriented trauma therapy Somatic Experiencing®) and Bessel van der Kolk (professor of psychiatry specializing in post-traumatic stress disorders) would take such a keen interest in his work.

Porges had not yet interpreted immobilization as a defense strategy in animals as a potentially traumatic response in human beings. But his theory finally explained what Levine, Van der Kolk, Ogden, and a number of other body-oriented pioneers had known for so long: the path to trauma healing runs through the body. This is how the sense of safety can be trained and restored.

We are, and will remain, both human beings and mammals—and for our survival, we need relationships and interaction with others. These are, for many people, the most challenging areas of life, and here lie clear links with themes such as attachment, intimacy, love, and friendship.

Video?

This wonderful short film with Dutch subtitles offers a clear and accessible explanation of the entire polyvagal theory.

If you have questions after reading this article, please post them in the comments below so that others may benefit from your question too.

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I remember an afternoon when I came home from a bike ride in the rain. Not a dreary drizzle, but a real, solid downpour—the kind that soaks your clothes through and through and seems to rinse your thoughts clean at the same time. I stepped inside, changed, made coffee, and noticed something I found hard to name: I felt present. Not relieved to be indoors or sad that the ride was over, but simply present. Fully in the here and now.

It didn’t last long—a moment later I had picked up my phone, was typing a message, and was thinking about tomorrow. But for those few minutes, I had taste…

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For decades I have been fascinated by “how things work.” By “things” I mean above all our body, our brain, and our nervous system—but pursuing that curiosity quickly leads to the question of how all of this came to be1. From there it is only a small step to evolutionary theory, the emergence of the human sciences, and, from there, Buddhist philosophy and psychology.

Over the years I have collected and studied a fair amount of reading material on these themes2, but also on science in general. What struck me repeatedly while reading about scientific developments was how painfully slow the acceptance of new insights can be—especially when those insights connect different disciplines or domains.

In the current wave of negativity surrounding the polyvagal theory I see a parallel, and that is why I felt it was time to examine and write an essay about a number of past scientific discoveries and their journey toward acceptance. What can these stories teach us about how science deals with criticism3?

A scientist who poisoned himself

In 1984, the Australian physician Barry Marshall did something his colleagues considered completely insane. He took a petri dish in which he had cultured a bacterium, mixed the contents with a small amount of liquid, and drank it. Not just any bacterium, but a micro-organism he claimed caused stomach ulcers.

The medical establishment at the time was absolutely convinced of its wisdom: stomach ulcers were caused by stress, too much coffee, spicy food, and a hectic lifestyle. Everyone knew that. Treatment consisted of sedatives, antacids, and advice to slow down. That a bacterium might cause stomach ulcers? Impossible. The stomach was far too acidic for bacteria to survive in. That was basic biology, and Marshall apparently was not clever enough to grasp it.

A few days after his self-experiment, Marshall began to feel terrible. He suffered from bloating, his breath became foul, and he was vomiting in the mornings. When he underwent an endoscopy, his stomach lining was found to be severely inflamed. The bacterium he had swallowed—later named Helicobacter pylori—had struck. Marshall had proved what he set out to prove: this bacterium caused inflammation of the stomach lining, and from that inflammation a peptic ulcer could develop.

It would take nearly ten more years before the medical world took him seriously. In 1994, a major conference in the United States finally concluded that he was right: stomach ulcers were indeed caused by a bacterium, and they could be cured with antibiotics. In 2005, Marshall and his colleague Robin Warren received the Nobel Prize for their discovery.

Why did it take so long? Why did a scientist have to literally make himself ill to be heard? And why is this pattern—a scientist discovers something, is ridiculed, and years later is vindicated—so persistently recurring throughout history?

The man who moved continents

If you look at a world map, you notice something remarkable. The eastern coastline of South America fits suspiciously well into the western coastline of Africa—as if someone had pulled two puzzle pieces apart. German scientist Alfred Wegener made the same observation in 1912, but he went further than merely looking. He gathered evidence from several corners of science.

Wegener was, in fact, a meteorologist, someone whose work concerned weather and climate, but his interests were broad. Reading articles on fossils, he encountered something puzzling: the same ancient plant and animal species were found in both South America and Africa. How was that possible? Those creatures could not have swum across the ocean. Traces of ancient glaciers appeared in places that are now tropically warm. And rock formations on either side of the ocean resembled each other strikingly.

Wegener conceived an explanation that at the time seemed utterly nonsensical: the continents had once been joined. He called this supercontinent Pangaea, meaning “all lands.” Roughly 300 million years ago, this mega-continent had broken apart, and ever since, the various pieces had been drifting slowly away from each other. South America and Africa had literally drifted apart.

The geological community’s reaction was devastating. Wegener was not a real geologist—what could he possibly know about it? Moreover, he could not explain how continents might move across the hard ocean floor. The prominent British geophysicist Harold Jeffreys calculated that it was physically impossible. The forces Wegener proposed—a kind of pull from the Earth’s rotation—were far too weak to displace enormous landmasses.

At a 1926 conference in New York, Wegener was publicly ridiculed. Speakers were sarcastic and sometimes outright insulting. A geologist who later recalled that period said, “I once asked one of my professors why he never spoke about continental drift. He answered scornfully that he might consider it if I could prove that a force existed capable of moving continents. The idea was complete nonsense, I was told.”

Wegener died in 1930 during an expedition in Greenland, aged fifty. He never knew he was right. It would be until the 1960s before his ideas were taken seriously.

In the 1950s, an American cartographer, Marie Tharp, began working with data from the ocean floor. Tharp was not permitted to join the research ships herself—women were not welcome on board—so she worked in the office with the measurements sent back from sea. From those dry numbers she constructed detailed maps of what lay beneath the water.

There she discovered something remarkable: running straight through the Atlantic Ocean was an enormous mountain range, the Mid-Atlantic Ridge. More striking still was a deep cleft running along the center of that range, a rift valley. When she told her colleague Bruce Heezen, he was skeptical—it seemed as though she wanted to breathe new life into Wegener’s old fantasies. But Tharp was right.

That mountain range turned out to be the place where new ocean floor was being created. Molten rock welled up, solidified, and pushed the older ocean floor aside. Other scientists found magnetic patterns in the rocks that confirmed it. Gradually the realization grew: the ocean floor is continuously renewed. New crust appears along underwater mountain ridges; old crust disappears into deep trenches. And those moving plates carry the continents with them.

By the mid-1960s, plate tectonics—the refined version of Wegener’s continental drift—was generally accepted. But Wegener himself had died thirty years earlier, ignored and mocked by the scientific establishment. And Marie Tharp, whose maps had provided the crucial evidence, received recognition only decades later. Her name was often absent from the publications her work had underpinned.

Darwin and the earth that was too young

Charles Darwin wrote his famous book On the Origin of Species in the two decades before its publication in 1859. The idea was simple yet revolutionary: species change over time. Through natural selection, better-adapted variants survive and pass their traits on to their offspring. Over millions of years, this leads to enormous diversity and the emergence of new species.

Within twenty years, most scientists were convinced that evolution was a fact4. Species had not been created in immutable form but developed over time. Yet there was one colossal problem to which Darwin had no answer: the time required.

William Thomson (later Lord Kelvin), one of the most respected physicists of his era, had calculated the age of the Earth. Starting from a molten fireball that gradually cooled, he concluded the Earth was between 24 and 400 million years old. That sounds impressively ancient—certainly far older than biblical accounts suggest—yet it was far too short for Darwin’s gradual evolution. Darwin needed billions of years, not millions.

Darwin was keenly aware of the problem. In 1869 he wrote to his colleague Alfred Wallace, “Thomson’s views on the recent age of the world have been one of my sorest troubles.” He believed he was right but could not substantiate it with hard figures.

There were further difficulties. How were traits passed from parents to children? Darwin did not know. Genetics did not yet exist5. There were also great gaps in the fossil record. Where were all the transitional forms? Critics such as the engineer Fleeming Jenkin argued that variations had a natural ceiling: you could selectively breed larger cattle, but growth eventually stopped. How then could you move from one species to an entirely different one?

Interestingly, biologists did accept evolution, but often not Darwin’s mechanism of natural selection. In France, Lamarck’s theory remained more popular well into the twentieth century. Lamarck held that organisms passed on traits acquired during their lifetime to their offspring: a giraffe that repeatedly stretched its neck to reach the highest leaves would produce offspring with longer necks. This theory also sat more comfortably with the moral climate of the time—you could improve yourself, and that improvement would be inherited.

The breakthrough came only in the 1930s: the integration of Mendelian genetics with Darwinian natural selection. The discovery of mutations and heredity via genes solved the problem of inheritance. Radioactive dating showed that the Earth was billions, not millions, of years old. Lord Kelvin had simply not accounted for radioactivity, a phenomenon unknown in his day6. The “Modern Synthesis,” or Neo-Darwinism, integrated genetics with evolutionary theory. Only then—seventy years after Darwin’s publication—was natural selection fully accepted.

Germs in a world of miasmas

Well into the nineteenth century, physicians and scientists believed that diseases were caused by “miasmas.” Miasma comes from Greek and literally means “pollution” or “contamination.” A kind of toxic vapor, it was thought, rose from rotting material. If you came near sewers, swamps, or corpses, you inhaled that poisonous air and fell ill7. The Black Death, the plague that killed millions across Europe, was explained by such noxious emanations.

Against that backdrop, in the 1860s a French chemist named Louis Pasteur proposed a radical theory. Diseases were not caused by bad air but by microscopically small organisms: bacteria. These germs were so tiny they could only be seen through a microscope, yet they were everywhere8. And when they entered the body, they could cause illness.

The resistance was immense. Rudolf Virchow, a celebrated German pathologist, mocked Pasteur. He is said to have declared that he had never looked through a microscope and had no intention of doing so. His argument against germ theory sounded logical: “If microbes were responsible for diseases, and they are everywhere, we would all be ill.” What Virchow did not understand was that the immune system can fight off most germs and that disease results only under specific circumstances.

Across Europe and also in the United States, Pasteur’s theory was vigorously contested by medical professionals who did not want to accept the change. This was a fundamental shift in how medicine was practiced. If diseases came from germs, then instruments had to be sterilized, hands had to be washed, and patients had to be isolated—a completely unique proposition from simply ensuring fresh air.

Pasteur himself was not a physician but a chemist. He had begun by studying wine fermentation and discovered that micro-organisms were responsible for the process. He then applied that knowledge to diseases in silkworms and later to infectious diseases in humans and animals. He was, in short, an outsider to medicine who solved a medical problem from an entirely different discipline.

Other scientists added pieces to the puzzle. The Hungarian physician Ignaz Semmelweis showed that puerperal fever occurred far less often when doctors washed their hands. The English physician John Snow traced a cholera outbreak in London to a specific water pump contaminated with sewage. The English surgeon Joseph Lister began sterilizing instruments with carbolic acid, and suddenly far more patients survived operations.

By the end of the nineteenth century, most scientists were convinced. The German physician Robert Koch formulated criteria in 1884 for establishing whether a specific bacterium causes a specific disease. He identified the bacteria responsible for anthrax, tuberculosis, and cholera. Germ theory became a cornerstone of modern medicine. The journey from miasmas to microbes had taken roughly thirty years—thirty years during which physicians like Semmelweis suffered mental breakdowns because no one believed them, patients died of infections that could have been prevented, and a new truth fought against old certainties.

Proteins that cause infection

In 1982 neurologist Stanley Prusiner made a claim that overturned much of what biologists and physicians knew about infection. He had isolated the infectious agent responsible for scrapie, a disease in sheep. It turned out to be neither a virus nor a bacterium. It was a protein—an ordinary protein, without DNA or RNA.

That was impossible. The central dogma of molecular biology states that information flows from DNA to RNA to protein. That is how organisms reproduce, how life “works.” A protein without genetic material that can replicate itself? This contradicted everything that was known.

Prusiner named this infectious protein a “prion,” derived from “proteinaceous infectious particle.” His idea was that a normal protein found in everyone’s body sometimes assumes the wrong shape. That misfolded form is stable and can force other, normal proteins to adopt the same wrong shape—a kind of domino effect. These misfolded proteins accumulate in the brain and cause fatal diseases such as BSE (mad cow disease) and, in humans, variant Creutzfeldt–Jakob disease.

The scientific world reacted with enormous skepticism. Prusiner was contradicted and ridiculed. For two decades he endured the mockery of his colleagues. Even prominent scientists such as David Baltimore, himself a Nobel laureate, were among the doubters. Some scientists persisted in claiming that an undiscovered virus must be involved. A protein alone simply could not transmit disease.

But Prusiner held on. He identified the specific protein and demonstrated that it occurred in two forms: a normal variant present in everyone and a disease-causing form folded differently. He conducted experiments showing that prions were resistant to treatments that normally kill viruses and bacteria—such as radiation that damages DNA—indicating that this was not a virus but a protein, albeit one extraordinarily stably folded and resistant to most methods that ordinarily break proteins down.

In the 1990s the BSE epidemic broke out in Great Britain. Thousands of cattle fell ill and had to be destroyed. Worse still, people who had eaten infected meat developed a variant of Creutzfeldt-Jakob disease. Suddenly this was no longer a theoretical discussion but a real public health emergency.

The tide turned. More and more scientists concluded that Prusiner might well be right. In 1997, fifteen years after his first publication, he received the Nobel Prize.

What these stories share

When you place all these examples side by side, several patterns emerge.

First, not one of these scientists could tell the complete story at the time of their first publication. Marshall had not conducted randomized trials. Wegener did not know how continents moved. Darwin did not understand how traits were inherited. Pasteur could not yet determine which specific bacterium caused which disease. Prusiner could not explain every detail of prion replication.

Yet the absence of a complete mechanism proved to be no reason to reject the entire theory. Later research and the growth of knowledge filled the gaps. For Wegener, it was oceanography that provided the key. For Darwin it was genetics. For Pasteur it was microbiology. For Marshall it was clinical trials with antibiotics. For Prusiner it was the structural biology of proteins.

Second, all of these theories ran directly counter to established convictions. Continents did not move—everyone knew that. Species had been created immutably. Diseases came from bad air. Stomach ulcers came from stress. Infectious diseases came from viruses or bacteria, always with DNA or RNA. These ideas formed the paradigms of their time—the worldview on which scientists based their work, the firmly anchored scientific consensus.

Third, these scientists were often not taken seriously because they were “outsiders.” Wegener was a meteorologist, not a geologist. Darwin was a naturalist without a formal academic position—essentially an amateur—not an established scholar at a university. Pasteur was a chemist, not a physician. Marshall was a gastroenterologist, not a microbiologist. Prusiner was a neurologist, not a molecular biologist or biochemist. That they came from another field was used against them. They could not possibly grasp the finer points of the discipline.

But it was precisely that outsider status that gave them an advantage: they saw connections that specialists overlooked. Wegener combined geography, paleontology, and climatology. Darwin brought biology and geology together. Pasteur applied chemical knowledge to medical problems. Marshall linked clinical observations with microbiology. Prusiner united neurology and biochemistry. They looked over the fence of their discipline and saw a larger picture.

It is inevitable that you become an outsider when you publish a theory spanning multiple fields. That also explains a significant part of the fierce resistance: cross-domain theories are judged by each discipline at their weakest points.

The problem of crossing domains

That last point—the cross-disciplinary character—deserves closer examination because it explains much of the resistance.

Scientific disciplines are like countries with their language, culture, and laws, written or unwritten. Geologists employ different methods than biologists. Anatomists look at the world differently than psychologists. Every discipline has its standards for what counts as evidence, its journals, and its experts who determine what is publishable.

If you develop a theory that fits within a single field, your work is assessed by experts in that domain. They examine your methods, your data, and your reasoning. If it is sound, they accept it. If it is weak, they reject it. That system works reasonably well.

The paradox is that precisely the apparent “weakness”—not “being fully at home in a given field”—is what creates space for out-of-the-box thinking. A specialist would never ask certain questions because they do not fit within the paradigm of that field. An outsider asks exactly those uncomfortable questions.

Geologists looked at Wegener and saw the mechanism does not work; the forces are too weak. That was true. But they did not see the strength of the paleontological and climatological evidence because that was not their area of expertise.

Biologists looked at Darwin and saw the mechanism of inheritance was missing; the timescale was wrong. Also true. But they missed the geographical and anatomical patterns that Darwin found so compelling.

With Pasteur it was clinical medicine. He was not a physician; he had not treated patients. That was accurate. Medical practitioners looked down on this chemist who thought he could tell them how diseases worked. But they did not see the strength of his experimental evidence.

With Marshall it was the absence of large clinical studies. One self-experiment does not make science, critics said. Where were the randomized trials? Yet his microbiological observations were correct, and when the trials came, they confirmed his hypothesis.

With Prusiner, it was the apparent impossibility of proteins without nucleic acid. That contradicted molecular biology. Critics kept searching for hidden viruses. Yet his biochemical work was meticulous and careful.

And today? Anatomists look at the polyvagal theory and see the anatomical details do not match exactly as described. Porges suggests that different vagal systems operate independently, but anatomists observe that the nerve fibers that slow the heart originate from different nuclei in the brainstem and work together rather than as separate entities. That too may be true. But anatomists do not necessarily see the clinical value, the therapeutic applications, or the explanatory power for trauma responses—because that is not their area of expertise.

The problem is that no one surveys the complete picture. Each discipline judges the work on the aspects that concern it and that it understands. And when you work across domains, there is almost always a discipline where your work is vulnerable—perhaps because you do indeed make errors in that field, perhaps because you are not familiar with the latest insights there, or perhaps simply because you, as a generalist, do not have the depth of knowledge of a specialist.

This is why cross-disciplinary theories attract so much criticism. Every discipline sees the weak spots within its domain. And that criticism can be entirely valid. Darwin genuinely did not know genetics. Wegener genuinely lacked a mechanism. Those points of criticism were legitimate.

But what critics often miss is the synthetic power of a theory—its capacity to bring together different puzzle pieces from different fields into a new picture. That is precisely where the strength of a cross-domain theory lies, and it is precisely what specialists do not always see.

The role of time and technology

In virtually all of these examples, time played an important role. It took decades before the theories were accepted—sometimes because new generations of scientists grew up unencumbered by the old prejudices, but often because new technologies produced evidence that had previously been impossible to gather.

Wegener’s theory only gathered momentum when sonar techniques could map the ocean floor, when scientists used magnetometers to measure magnetic patterns in the seabed, and when seismographs could trace earthquakes across the globe. None of those techniques existed in Wegener’s time.

Darwin’s theory was confirmed when genetics developed, when microscopes became powerful enough to observe chromosomes, and when radioactive dating revealed the true age of the Earth. Darwin did not have those tools.

Germ theory benefited from better microscopes, from techniques for culturing bacteria, and from the discovery of viruses as microscopes grew still more powerful.

Marshall’s work was confirmed when antibiotics became available and it could be shown that stomach ulcers disappeared when the bacterium was killed.

Prusiner’s work gained support when proteins could be purified and their structure determined at a molecular level.

Occasionally an idea is simply ahead of its time. The tools to prove it do not yet exist. The framework to understand it is not yet in place. That is why a theory may have to wait decades before the rest of science catches up.

Not every criticized theory is rehabilitated

There is another important aspect that belongs in this essay. For every theory that survived criticism and was eventually accepted, many others were criticized and rightly rejected. Those stories deserve attention too, because they show that criticism can have good reason.

Consider the phlogiston theory of the eighteenth century. Scientists believed that combustible materials contained a substance released during burning—phlogiston. This theory had adherents for decades, was defended by prominent chemists, and seemed to offer an elegant explanation for a range of phenomena: why things burn, why fire goes out in an enclosed space, and why metals rust. But there was a problem: metals became heavier when they burned, not lighter. The theory required increasingly elaborate adjustments to explain this, such as “negative phlogiston.” In the end, Lavoisier’s oxygen theory made the entire construction superfluous.

Or consider cold fusion in 1989. Two scientists claimed to have achieved nuclear fusion at room temperature—which, if true, would have solved the energy crisis. The press was euphoric. Laboratories across the world attempted to reproduce the results. A few claimed success. But gradually it became clear that it did not work. The original experiments had rested on measurement errors and overconfidence.

Or polywater in the 1960s and ‘70s. A Russian scientist believed he had discovered a new form of water with bizarre properties. International labs studied the phenomenon; publications, conferences, and discussions followed. It turned out to be nothing more than contaminated water.

Or vitalism—the idea that living organisms contain a special “life force” that makes them fundamentally different from dead matter. Popular in the nineteenth century and enjoying considerable scientific support, vitalism was gradually undermined as biochemistry and molecular biology demonstrated that life processes are simply complex chemical reactions. No special force required.

These theories shared something with the examples that eventually proved successful: they were defended by eminent scientists, they had supporters and opponents, they attracted fierce criticism while their proponents held firm, and they promised revolutionary insights. Yet they were mistaken.

What makes the difference?

This is a meaningful question—particularly when we later look more closely at the polyvagal theory. If you are in the middle of such a scientific struggle, how do you know whether you are a Darwin or a defender of phlogiston? In hindsight it is easy to see, but during the process?

Patterns can be distinguished, though they offer no guarantees. Phlogiston required ever more complicated assumptions to explain observations. Cold fusion could not be consistently reproduced. Polywater vanished the moment more careful work was done. Vitalism became increasingly redundant as science advanced. These theories were not merely rejected because of new insights; above all, they eroded because they failed to deliver on their promises.

The theories that did survive—evolution, plate tectonics, germ theory, prions—had a different dynamic. They began rough and incomplete but became more robust as more research accumulated. They predicted things that were later confirmed. They opened fruitful lines of inquiry. They converged with evidence from an ever-growing number of disciplines, rather than diverging.

Darwin predicted transitional forms that were found decades later. Wegener’s continental drift received support from oceanography, seismology, and paleomagnetism—entirely different fields that independently arrived at the same conclusion. Pasteur’s germ theory led to antisepsis, vaccination, and antibiotics—practical applications that worked. Prusiner’s prions explained an ever-growing number of diseases as molecular biology advanced.

The difference lies not in the quantity of criticism nor in how long a theory withstands resistance. The difference lies in what happens as the investigation continues. Do the problems grow, or do they resolve? Do explanations become more complicated or simpler? Do different lines of research converge on the same conclusion or point in different directions?

For cross-domain theories, there is something more. The theories that survived—evolution, plate tectonics, and germ theory—ultimately became stronger through interdisciplinary research. Biologists collaborated with geologists, chemists with physicians, and neurologists with biochemists; the disciplines reinforced each other and filled each other’s gaps. With the theories that disappeared, such as vitalism or the ether theory, the opposite happened: as disciplines developed, they rendered the theory increasingly redundant.

This may be the most important distinction. A viable cross-domain theory builds bridges between disciplines that remain standing even as details are adjusted. It opens new fields of inquiry, poses new questions, and leads to productive collaborations. Flawed cross-domain theories merely fill temporary gaps in knowledge and disappear once those gaps are filled by other means.

But these too are criteria that can mainly be applied in retrospect. During the process itself, the distinction is often not sharp. That is precisely why scientific skepticism is so valuable: it ensures that only theories capable of withstanding continuous scrutiny survive.

The polyvagal theory in perspective

Against this background, it is interesting to look at the polyvagal theory. This theory, developed by Stephen Porges—who worked on it from the 1970s and formally introduced it in 1994—seeks to explain how our autonomic nervous system responds to safety and danger and how this influences social behavior and emotion.

The theory combines neurobiology, evolutionary biology, psychology, psychiatry, and trauma therapy. It is a cross-domain theory par excellence. And, like the historical examples, it attracts criticism from multiple directions.

Anatomists and neuroscientists point to anatomical details that do not hold up. The “ventral vagal complex,” as Porges describes it, is said not to exist as a separate anatomical entity. Claims about unique mammalian innovations in the function of the vagus nerve are disputed. The details about which fibers travel where do not always appear to match what anatomy reveals.

That criticism is important and must be taken seriously. If the anatomical foundation of a theory does not hold, that is a real problem.

Yet at the same time, therapists, psychologists, and other professionals find great value in the theory. The concepts of neuroception (the unconscious detection of safety or danger), of a hierarchy in stress responses, and of the connection between autonomic regulation and social behavior prove to be clinically very useful. Trauma treatment has been influenced by them. The understanding of autism, anxiety disorders, and PTSD has benefited from them.

A tension thus arises between science and practice. Different disciplines see different things. Anatomists see anatomical errors. Therapists see therapeutic value. Both observations can be true simultaneously.

We genuinely do not know how this story will end. The polyvagal theory is not yet complete—Porges himself does not dispute this. He is willing to adapt his theory, responds to criticism, and refines his claims. The scientific discussion is ongoing. And that is the difference from our historical examples: we look at those with the wisdom of hindsight. We know how their stories ended. With the polyvagal theory, we are still in the midst of the process.

Perhaps this theory will follow the same path as evolutionary theory and plate tectonics: a large core of truth that is initially rough and imprecise but is gradually refined and accepted. Perhaps it will emerge, fifty years hence, that Porges was essentially right, even if details had to be adjusted. The theory is already opening fruitful lines of inquiry, gaining support from multiple therapeutic traditions, and demonstrating practical value—all characteristics that the successful theories displayed as well. Perhaps a refined, more complete theory of the autonomic nervous system will be developed that integrates certain insights from Porges.

We simply do not know. The history of science does not teach us that every cross-domain theory that attracts criticism will ultimately be vindicated. It teaches us that such theories must be assessed in a particular way and that the process of acceptance or rejection can be complex and lengthy.

What we do know is that Stephen W. Porges has published more than 400 articles on the PVT9. These are not “unfounded” scientific claims. His work is a beautiful transdisciplinary synthesis, one that remains incomplete—and Porges himself is aware of that.

As Porges recently wrote10:

Polyvagal theory emerged from my efforts to bridge psychological processes and autonomic function, drawing on insights from neurophysiology, neuroanatomy, clinical medicine, and the study of brain–body connections across disciplines. Developing this theory illuminated a fundamental challenge in science today: disciplinary silos often restrict collaboration and the integration of knowledge, as specialized methods and language can inhibit the exchange of ideas. When research remains isolated, advancing collective understanding becomes more difficult. This study examines the development of PVT and articulates its core principles in light of interdisciplinary engagement—particularly with colleagues unfamiliar with the theory's foundational literature. Bridging such gaps requires not only sharing knowledge but also cultivating openness to new perspectives, intellectual flexibility, and a spirit of curiosity about ideas that challenge established assumptions.

What can we learn from this?

An important lesson seems to be that science always contains a tension between specialization and synthesis—and we need both. We need experts who know every detail of their field, who can spot errors, and who maintain standards. Without them, science would descend into speculation and fantasy.

But we also need generalists who draw connections between disciplines, who ask new questions, and who dare to think outside the box. Without them, science would become mired in ever-narrower specializations that no longer communicate with each other—leading ultimately, in the extreme case, to a specialist who knows everything about nothing.

What we see is that these two types of scientists often clash. The specialist sees the errors, the imprecisions, and the lack of depth. The generalist sees the new connections, the synthetic power, the larger picture. And both are partly right.

A second lesson is that time and patience matter. Wegener’s theory needed fifty years. Darwin’s vision needed seventy. Genuine insight and profound knowledge apparently take time. New generations must graduate without the old prejudices. New techniques must be developed. Puzzle pieces from different fields must come together.

A third lesson is that criticism is valuable, even when it ultimately proves unfounded. The criticism of Darwin forced evolutionary biologists to become better—to develop genetics to study fossil evidence more carefully. The criticism of Wegener forced geologists to investigate the ocean floor to discover mechanisms. Criticism sharpens theories, and by doing so may help them survive.

And despite all these lessons, we must be cautious with historical analogies. That Wegener was right does not mean that every scientist who attracts criticism will be vindicated. That Marshall won a Nobel Prize after years of ridicule does not mean that every rejected theory will be rehabilitated. Phlogiston, cold fusion, polywater, and vitalism remind us that criticized theories may be criticized with good reason.

A messy process

Some ideas come too early and die before their time arrives. Some scientists devote their lives to a theory that turns out to be wrong. Semmelweis ended his life in a psychiatric institution, broken because no one would take his handwashing hypothesis seriously.

Science beyond domain boundaries is not easy—neither for the theory nor for the scientist. It regularly invites criticism; it requires a particular way of evaluating, one that looks beyond the weak spots in individual fields and pays attention to the synthetic power of the whole.

But we must understand that we cannot use the past to justify the present. That Wegener was ultimately proved right says nothing about whether a current theory will be vindicated. Every theory must be judged on its merits—with nuanced criticism and attention to both weaknesses and strengths.

The stories of these scientists teach us above all: be open to new ideas, but also be critical. Do not dismiss too quickly, but do not accept too readily either. Pay attention to the criteria that distinguish successful theories from failures: convergence of evidence, predictive power, fruitful research programs, and practical applications that work. And recognize that science is a process unfolding over decades, with much uncertainty and few guarantees.

In conclusion

Can we say something meaningful about the polyvagal theory? I think so.

If we look at the criteria that distinguish successful theories from failures, we may recognize certain patterns in the polyvagal theory. It opens fruitful lines of inquiry: from the microbiome-gut-brain axis to parasympathetic biofeedback, from research into social signals to studies of body-based interventions. It is gaining support from different disciplines: not only psychotherapy, but also education, perinatal care, addiction care, and autism support are applying its insights.

There are practical applications that demonstrably work: trauma-sensitive care in hospitals and mental health settings, regulation interventions in education, and support for developmental trauma. Porges’s model serves as a physiological explanation for the success of various body-based trauma therapies, including Somatic Experiencing®.

And the theory is becoming more robust as research accumulates: Porges continues to respond to criticism and continues to publish—which is how science is supposed to work. It is precisely the pattern we saw with Darwin, Wegener, and many of the other scientists mentioned here: a rough beginning that is gradually refined, not a rigid construction that collapses at the first headwind.

The criticism that exists certainly contains elements that still need to be examined, and I will be writing about those in the period ahead. But that is, in my view, no reason to throw the baby out with the bathwater.

Something for a future essay: the manner in which the polyvagal theory is being criticized does not deserve a prize for elegance—it is more reminiscent of the heated debates of Darwin’s era than of a nuanced scientific exchange.

The question is not whether every anatomical detail is correct—Darwin did not know genetics; Wegener had no explanatory mechanism. The question is whether the theory is fruitful enough to advance our understanding and whether it brings different disciplines together in a way that proves durable. Of that I am convinced. The polyvagal theory has given me more insight into the connection between body, emotion, and behavior than any theory I have encountered in the past several decades.

Whether in fifty years Porges’s theory will look exactly as it does today? Probably not. But the same was true of Darwin’s theory of evolution.

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Around session four or five of the compassion training, I would often show the video below. It still moves me every single time. It is about sound and expectation—but for me it is above all about connectedness and our shared humanity, a central theme in compassion training.

In the video, Bobby McFerrin gives a whole new dimension to the phrase ‘playing the audience’… 😄 Watch and join in:

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Foreword

The article below was recently published in the Tijdschrift voor Begeleidingskunde (Journal of Guidance Studies), issued by the Dutch National Association for Supervision and Coaching (LVSC). I wrote it together with Cees van Elst.

In the course of writing the article, Cees and I decided to develop a Master Class: Polyvagal-Informed Guidance in Coaching Practice. You can read more about this on this page.

Our thanks go to the LVSC for the opportunity, and our compliments to them for their excellent and substantively rich journal—well worth reading for professional supervisors and coaches!—and to Cees for the enjoyable collaboration.

For the purposes of this English translation, we have revised and improved the original article in a number of places.

Polyvagal theory offers tools for working in a trauma-informed and process-oriented way, without taking the therapist’s seat. Coaches use knowledge of the nervous system to create a neurobiologically safe environment by centering self- and co-regulation rather than the coachee’s narrative. In this way, they naturally deal professionally with themes that involve insecurity.

The society in which we work is a performance-oriented, malleable society. The message is often, If things are not going well, something needs to be fixed (Schinkel, 2020). Pain, loss, disruption, and doubt are quickly medicalized (Trappenburg, 2021). Therapy and diagnoses are lurking, while many people do not actually need therapy but space and recognition. They are seeking a place where their experience can settle and slowly begin to move. In our practice as professional counselors, we increasingly see people who, from a medical perspective, appear to be ‘fine’ but who still do not feel free. They feel tired, tense, listless, or overwhelmed. They are not sure what is wrong, only that something appears to be wrong. And what about us as coaches or counselors? We sometimes have doubts too. Is this trauma? Is it burnout? Is it overwhelm? Should I refer them or stay? And if I stay, what can I ‘do’ with a person who is clearly not feeling well and where trauma may be playing a role?

We assume that many coaches know what to do: let them tell their story and offer ‘holding space’ in which the coachee feels safe, heard, and not judged (Plett, 2015). We assume that many coaches then also want to help coachees make sense of and fix their story. After all, that is often the request for help and the appeal: ‘Help me, I want to get rid of something; how do I do that? And where does it come from?’ In short, we start with the coachee’s story and too quickly descend into the psychological recesses of the soul, even though that is not our professional role. What if we were to involve physiology and unconscious bodily processes more consciously in our sessions?

In this article, we explore what coaches can achieve with physiological knowledge of polyvagal theory (Porges, 2011). In practice, this model has proven to be a workable framework that grounds our interventions. It has its origins in neuroscience and was initially applied mainly within trauma and psychotherapy practices (Porges, 2011; Dana, 2018). The theory provides language, insight, and scope for action in relation to what we sometimes already intuitively sense. We do not present ourselves as scientists but as practitioners. We explore how polyvagal theory can help professional counselors be present with their clients with greater confidence, gentleness, and somatic awareness. Because when viewed through a polyvagal lens, the question is not what happened, but what is happening here and now—in the body, in the space, in the relationship (Dana, 2020). The key question we are exploring is: how can a polyvagal-informed coach contribute to recovery, self-regulation, and meaningful movement—without it becoming therapy?

Polyvagal theory at a glance—a physical lens on human experience

Those who guide people always work with the body, even when the conversation remains entirely verbal. Polyvagal Theory (PVT), developed by psychologist and neuroscientist Stephen Porges (2011), offers an innovative and body-oriented perspective on how the autonomic nervous system constantly scans the world for safety and danger. More importantly, it shows how these unconscious processes determine what a person feels and thinks and how they behave. The theory does not provide counsellors with diagnoses, but rather a lens through which to understand behaviour and experience via the state of the nervous system.

Three Functional Systems

The autonomic nervous system (ANS) independently regulates those things that we do not need to use our minds for, such as body temperature, heart rate, breathing, digestion, pupil size, and other automatic processes that are vital to life. The ANS consists of the sympathetic part (activating, like a ‘gas pedal’) and the parasympathetic part (calming, like a ‘brake’). Examples include an accelerated heart rate during stress (sympathetic) and a slowed heart rate during relaxation (parasympathetic) (Bear, 2020).

Porges adds an extra layer to this in his polyvagal theory: he describes the ANS not as two, but as three functional systems that are organized hierarchically, based on evolutionary age. In response to unconscious assessments of (un)safety, the ANS shifts between three primary states (Porges, 2011; Dana, 2020):

1. Ventral vagal system: the evolutionarily youngest system, which focuses on social engagement and connection. This system becomes active when safety is experienced. People feel calm, connected, curious, and capable of social contact. In this state, they can reflect, play, learn, attune, and recover. When there is a mild threat—for example, someone looks angry after a comment—the ventral system can help prevent escalation by sending additional signals of connection and safety.

2. Sympathetic system: is older than the ventral part and comes to the fore in the event of threat or stress. The body prepares itself to fight or flee. People become alert, tense, angry, or anxious. Their focus narrows, and their connection with others diminishes. Even when safe, the sympathetic system can be activated. This creates sympathetic activation combined with connection, as we see in sports, play, and engaged work.

3. Dorsal vagal system: the oldest system. It becomes active when fighting or fleeing is no longer possible. This system switches to immobilization or freezing. People feel numb, withdrawn, powerless, or dissociative. In extreme forms, this leads to depressive or dissociative states (Dana, 2020). In safety, this system regulates our basic homeostatic processes, such as digestion and metabolism, and plays a vital role in our health.

This classification is often represented as an ‘autonomic ladder’ (Dana, 2020). We automatically move up and down this ladder continually throughout the day, depending on what the body registers as safety or threat. Although the ladder is widely used, it has shortcomings, just like any model. We have chosen to use an autonomic mixing panel as a metaphor for the three autonomic states (de Caluwé 2025).

Neuroception

The detection of safety or threat occurs outside of conscious awareness. Porges introduced the term ‘neuroception’ for this: an automatic and non-cognitive process in which the nervous system continuously scans signals from the body (interoception), the environment (exteroception) and interactions with others (co-regulation) (Porges, 2004). This process occurs in the oldest brain structures, though the exact mechanisms remain unclear. Neuroception determines whether a situation is perceived as safe or unsafe, even before thoughts or interpretations arise.

Voice use (prosody), facial expression, body posture and movement, the layout of a room (including its scent), and signals from the body can influence this assessment (Dana, 2018). You can think of neuroception as the hand that operates the autonomic mixing panel.

Our knowledge of neuroception provides coaches with a crucial tool for influencing autonomic states in their professional practice. This allows us to shift from psychological understanding to physiological comprehension.

Our bodies exist in an era for which they were not designed. Our nervous system and stress system are still the same as they were some 300,000 years ago. However, the amount of stress and stimuli has increased exponentially. Our ‘ancient’ stress system is unable to distinguish between physical danger (a sabre-toothed tiger chasing us) and psychological threat (a client sending a critical email).

A neuroception of unsafety increases the likelihood that our ventral vagus will be less active than ‘normal’—or more accurately, than what is natural and healthy. People with reduced ventral vagal tone experience diminished connection with others and have limited access to positive feelings, including (self-)compassion. Their learning ability also decreases.

Co-Regulation

Co-regulation is the effect of interpersonal interaction on the capacity to regulate one’s physiological state (bodily sensations and emotions). All relationships involving connection revolve around co-regulation. We learn to co-regulate in our early years, with the help of well-regulated parents or carers. Co-regulation is not a luxury; it is a biological requirement for our survival.

The need for human contact varies from person to person, but no one can do without it. People who claim they don’t need others likely live with a chronically activated nervous system.

As a coach or counselor, co-regulation means that you yourself serve as a regulatory instrument. Your tone, posture, speech, pace, and presence influence the state of your coachee’s nervous system and vice versa. Whether you invite connection or unintentionally evoke threat is largely registered somatically—not through rational reasoning.

If polyvagal theory can explain much of our behavior based on the functioning of the autonomic nervous system, then the theory is also relevant for coaches. For coaches, PVT-informed work means being consciously present with what emerges in the body and in the relationship, without analyzing or attempting to solve it. Because the nervous system does not want to be understood, it wants to be felt and encountered (Van der Kolk, 2014).

Example 1: Checking in

Marjan enters the practice hurriedly, her face red. “Phew, almost late,” she gasps, and sits down. “But I’m here!” She immediately begins her story about recent events. The coach notices that the coachee has clearly not yet landed (sympathetically activated) and indicates that it is important to check in first. “Breathe calmly and focus on your breathing.” Meanwhile, he counts her respiratory rate and notices it decreasing from 20 to 12 breaths per minute. He asks, “Are you more grounded now?” “Yes,” she says immediately. “Okay, Marjan, what do you want to talk about today?” Marjan immediately launches into her story.

In the above example, a lot seems to be going well. The coach notices the sympathetic activation (which was almost impossible to miss) and intervenes to help the coachee regulate so that the session time can be used effectively. However, signs suggest that Marjan remains sympathetically activated. The tone of her “Yes” is hurried, and she gets straight to the point. Activation to this degree means that the ventral part of the coachee’s autonomic nervous system may still be insufficiently active, preventing optimal connection and openness. That does not mean that the session cannot be valuable, but from a polyvagal perspective, a different start to the session would have been possible (please be patient; you are almost at example 2).

Applying polyvagal theory in a coaching session

Rather than responding immediately to the narrative content (’what happened?’), PVT invites us to first attune to the coachee’s physiological state (’what is the current setting of this person’s autonomic mixing panel?’). From this perspective, it becomes clear why one coachee talks actively and urgently (sympathetic activation), while another barely makes contact and appears absent (dorsal activation). Or why someone calms down when you, as coach, simply remain fully present without ‘doing’ anything (ventral regulation through co-regulation). What matters is that the coach offers connection without forcing the other person to connect as well. Any pressure on a trust-building process—which coaching fundamentally is—proves counterproductive. After all: if genuine trust exists, why would such pressure be needed? The coachee’s nervous system is often sensitive to this, especially in cases of trauma. The coachee might say something like, ‘I’m not very talkative today.’ However, this may be a rationalized explanation for an unsafe neuroception that arose because the coach unconsciously pressured the coachee. This can occur when the coach over-directs or absorbs the coachee’s arousal.

Slowing Down and Bearing With

The necessity of embodiment in the coach is therefore a key practical implication of PVT. In other words, as a coach, you are present not only cognitively but primarily through your body, breath, facial expressions, voice, and nervous system. You remain aware of your own state—even if slightly activated—provided you can ground yourself in it and slow down. Only a regulated nervous system can provide safety to another (Siegel, 2010).

Slowing down and bearing with are key concepts here: slowing down to notice what is happening somatically and bearing with to remain present with the other’s tension or discomfort without attempting to resolve it. This requires an attitude of ‘mutual inquiry’ (Epstein, 1999): exploring together, with curiosity, what the body is communicating, without judgment. ‘Mutual’ also implies ‘equal’—the coach need not have answers and must be able to abide in ‘not-knowing.’ Now we enter the ‘magical’ field where space can open, insights emerge, and discoveries unfold.

“Shut Up and Be Present!”

Co-regulation does not work through words, but through the relationship. The autonomic nervous system registers various safety signals that coaches can consciously employ. These include calm breathing, a warm vocal tone, and non-intrusive eye contact. This means that a simple coaching stance of silence and presence often proves more effective than any tool or technique (Dana, 2020).

The challenge for coaches is therefore not determining what to say or do, but rather how to be present. Am I regulated? Can I relate to the tension without taking it over, without pushing, without avoiding it?

Self-Regulation

Coaching from a polyvagal perspective means helping coachees recognize, normalize, and ultimately regulate their own autonomic responses. This requires coaches to develop somatic awareness, articulate physical sensations, and build experiential knowledge of ‘the mixing panel.’ Not through explanation alone, but through embodied experience, slowing down, and self-regulation. Self-regulation begins with learning to recognize signals: ‘When do I notice myself drifting, withdrawing, or accelerating?’ Co-regulation supports this process: through your attunement, presence, and calm, the other can re-experience safety. Only from that basis is reflection possible.

Example 2: Co-regulation

Marjan enters the practice hurriedly, her face red. “Phew, almost late,” she pants, and sits down. “But I’m here!” She immediately starts telling her story about recent events. The coach notices that the coachee has clearly not yet settled down (sympathetic activation) and also notices that this is affecting him; he experiences a restlessness that was not there a moment ago. He allows Marjan time to check in and breathe more calmly, then checks in with himself (slowing down). He consciously sits differently and breathes in and out calmly (slowing down, self-regulation). He notices himself calming down and can now look at Marjan with a gentle smile and ‘soft eyes’. Marjan says, “I’ve settled down now.” Nevertheless, he notices that Marjan still sits tensely, her eyes remain slightly widened, and her facial muscles appear somewhat ‘tight’. Moreover, her voice remains somewhat ‘elevated’, and her abdomen appears uninvolved in her breath. The activation has not really calmed down yet. “Okay,” says the coach, “I’m glad you feel you’ve settled, Marjan. How do you sense that in your body right now? Shall we explore that together?”

In this encounter, the coach invites the coachee to become curious and inhabit the here-and-now without hurrying (slowing down). The here-and-now is essential for connection and increased ventral vagal activation. A sense of calm emerges, creating space to explore the coaching question. Neither coach nor coachee knows where this will lead. But if the coach trusts that the coachee will discover insights and perhaps even answers, movement will emerge, allowing them to explore the question together from within the connection.

Traces of Trauma

Most coaches are not therapists. Yet it is virtually impossible for coaches not to encounter trauma. This is not because everyone is severely traumatized, but because trauma, broadly defined, is inherent to being human. In this example we don’t know whether a trauma part of Marjan was triggered, but her sympathetic activation could be related to this. Coaches speak of wounds, losses, shame, blockages, or unexplained reactions. These often contain traces of trauma, even if they are not identified as such.

The polyvagal theory also provides insight here and makes it possible to approach these themes without pathologizing or treating them. The nervous system’s response translates into behavior and aims to manage the situation as adaptively as possible. If someone could have avoided the freeze response through different means, they certainly would have. We won’t elaborate on what trauma is precisely, but we want to share Gabor Maté’s insight: ‘Trauma is not what happens to you, but what happens to you as a result of what happens to you.’

In example 2, we see that the coach creates an atmosphere of safety and connection, even though he does not know exactly what the underlying triggering problem is. From this position of not knowing, the coach can still slow down together with the coachee and create space so that the sympathetic activation can decrease. And then the coachee enters an entirely different session than in example 1.

Trauma-Sensitive Work

In our experience, many coaches recoil from signs of possible trauma dynamics: inexplicable reactions, intense emotions, avoidance behavior, ‘checking out,’ or freezing. Ien van der Pol wrote a clear guide for coaches on this topic: ‘I want the fear to disappear and for working with the effects of traumatic events to become more widely known among professional counsellors’ (Van der Pol, 2020). Practice reveals that the danger lies not in trauma’s content, but in how we engage with it. Attempts to fix, probe deeply, or accelerate can prove dysregulating (Van der Kolk, 2014; Van Elst et al., 2022). Repair implies something needs fixing—that something is ‘wrong’ with the coachee. In the ventral vagal state (calm, connection, and self-awareness, where nothing is ‘not-right’), both coach and coachee can welcome new perspectives and release old patterns (Dana, 2020).

A trauma-sensitive coach notices when the coachee becomes sympathetically or dorsally activated. The coach thus recognizes that the coachee’s autonomic nervous system detects something from the there-and-then in the here-and-now, triggering an unsafe neuroception and activating their survival mechanisms.

From a PVT-informed perspective, coaching focuses not on ‘repairing’ or resolving trauma, but on strengthening capacity for self- and co-regulation (containment). It is a fundamental way of supporting people in rediscovering their own movement, with the body as compass and the relationship as bedrock.

The coach as holding environment, not as solution machine

As we’ve seen, presence itself is physiological information. Rather than fixating on story or analysis, lived experience itself becomes the anchor of the coaching journey. This aligns with the polyvagal approach, in which the coachee’s state—not their story—guides the work. Hence the principle: ‘Story follows state’ (Porges, 2011).

This way of coaching requires not only knowledge of the nervous system but also ongoing self-reflection. The examples reveal how coaches can sometimes get swept up in their own survival responses: fixing, avoiding, over-regulating, and filling in gaps. Coaches can only provide a safe bedrock if they know themselves and can access their own ventral state. Professional coaches therefore work in trauma-informed and process-oriented ways but do not process trauma unless specifically trained to do so. Concretely, this means that training programs for professional coaches must invest not only in methodology but also in:

• (Neuro)physiological knowledge;

• Somatic awareness and interoception;

• Self-regulation skills;

• Knowledge of trauma responses;

• Creating space for trauma-sensitive reflection;

• Embodied learning, not just theoretical knowledge.

Fortunately, several such training programs in the Netherlands are recognized by the LVSC (Dutch National Association for Supervision and Coaching).

In a world where stress, burnout, and disconnection seem more the rule than the exception, coaching has become an in-between practice. Not therapy, not nothing, but something that moves in the space between. It is precisely in this space that polyvagal theory offers a workable lens: a way of seeing people that requires not diagnosis, but presence. This enables us to work with people who might otherwise benefit from therapy.

Key Element

When coaching people, you always work with the autonomic nervous system—whether aware of it or not. That is the central conclusion of this article. PVT-informed coaching means not treating trauma but learning to recognize someone’s autonomic state and how to offer safety at the nervous system level. This demands a fundamental shift in coaching practice:

• From analyzing to attuning: story follows state, not the reverse.

• From solving to regulating: you need not fix anything but must be able to hold and bear with it.

• From method to humanity: your presence is often your most powerful instrument.

Especially in our current era, when existential discomfort is often medicalized, coaches need language for life’s inherent pain, whether large or small. Language that normalizes rather than pathologizes. Polyvagal theory offers such language: practical, somatic, and relational. In this article, we have shown what that can look like. Coaches who work in a PVT-informed way:

1. Recognize signs of autonomic activation;

2. Can slow down rather than speed up;

3. Can remain present without ‘doing’;

4. Create space where regulation and healing can emerge, without directing.

These four capacities can be trained but demand an integrated, embodied foundational stance. The key lies in the coach’s fundamental trust that open exploration of an issue or question offers the greatest possibility for a fruitful session. In our view, coaches need more training in stress and autonomic nervous system physiology, self-awareness to recognize their own signs of autonomic activation, and supervision grounded in PVT-informed practice.

The authors will offer several masterclasses on ‘Polyvagal-informed and embodied coaching’ in 2026.

More information is available at www.relaxmore.net and www.heartfulatwork.nl.

You can download a PDF of the article:

The Bridge Between Nothingness And Therapy - De Caluwe and Van Elst

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Authors:

Ronald de Caluwé (1963) engages in compassionate bodywork through mindfulness, tai chi, and qigong. He is fascinated by polyvagal theory, writes about it regularly, and is a board member of the Dutch Polyvagal Institute. Website: www.relaxmore.net. Email: ronald@relaxmore.net.

Cees van Elst (1962) is an LVSC-registered coach working for the Academy for Medical Specialists. He is the owner of ‘HeartfulAtWork Coaching & Consultancy’ and a board member of the Dutch Polyvagal Institute. Website: www.heartfulatwork.nl. Email: cees.van.elst@heartfulatwork.nl.

References:

Bear, M. F., Connors, B. W., & Paradiso, M. A. (2020). Neuro-science: Exploring the Brain (4e editie). Wolters Kluwer.

Dana, D. (2018). The polyvagal theory in therapy: Engaging the rhythm of regulation. W. W. Norton & Company.

Dana, D. (2020). De polyvagaaltheorie in therapie: Het ritme van regulatie. [The polyvagal theory in therapy: Engaging the rythm of regulation]. Mens!

De Caluwé, R. (2025). Een nieuwe samenvatting van de polyvagaaltheorie. [A New Overview of Polyvagal Theory]. Online: https://www.relaxmore.net/p/een-nieuwe-samenvatting-van-de-polyvagaaltheorie.

Epstein, R. M. (1999). Mindful practice. JAMA, 282(9), 833–839.

Grossman, P., & Taylor, E. W. (2007). Toward understanding respiratory sinus arrhythmia: Relations to cardiac vagal tone, evolution and biobehavioral functions. Biological Psychology, 74(2), 263–285.

Plett, H., Smit, M. & Elstak, P. (2021) De kunst van Holding Space: Lessen in liefde, loslaten en leiderschap. [The art of Holding Space: lessons in love, letting go and leadership]. Het Noorderlicht.

Porges, S. W. (2004). Neuroception: A subconscious system for detecting threats and safety. Zero to Three, 24(5), 19–24.

Porges, S. W. (2011). The polyvagal theory: Neurophysiological foundations of emotions, attachment, communication, and selfregulation. W. W. Norton & Company.

Schinkel, W. (2020). De nieuwe democratie: Naar andere vormen van politiek. [The new democracy:towards alternative forms of politics]. Boom.

Siegel, D. J. (2010). The mindful therapist: A clinician’s guide to mind-sight and neural integration. W. W. Norton & Company.

Trappenburg, M. (2021). De zorgval. [The healtcare trap]. Boom.

Van der Kolk, B. A. (2014). The body keeps the score: Brain, mind and body in the healing of trauma. Viking.

Van der Pol, I. G. M. (2020). Coachen waar het pijn doet: Werken met trauma in coaching en begeleiding. [Coaching where it hurts: working with trauma in coaching and guidance]. SWP.

Van Elst, C., Van Rijssel, M., & Smit, L. (2022). Van vermijding naar bevrijding: Drie coachingswegen naar Zijn. [From avoidance to liberation: three coaching pathways toward embodied Presence]. Samsara.

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