Polyvagal Theory debunked in comprehensive new study

A recent paper co-authored by 39 leading scientists names the Polyvagal Theory (PVT) ‘untenable.’ It’s the work of two decades, with agreement from experts in wide-ranging fields. But some in the psychological community are hesitant to let PVT go.

InSight+ spoke with lead author Professor Paul Grossman about this latest paper, a lifetime of studying the topic, and why he thinks this truth is important.

Professor Paul Grossman has spent most of his career studying how the autonomic nervous system (ANS) affects the heart during challenging situations, and the last two decades challenging the validity of PVT, one of psychotherapy’s biggest hits.

Professor Grossman is a psychologist and psychophysiologist, and Emeritus Research Director of Psychosomatic Medicine at the University Hospital Basel, Switzerland. His most recent paper, ‘Why the Polyvagal Theory is Untenable,’ co-authored with 38 ANS scholars, was published in Clinical Neuropsychiatry.

The paper debunks key tenets of the Polyvagal Theory (PVT) from evolutionary and physiological standpoints.

Disconfirming Polyvagal Theory

The Polyvagal theory was developed by Dr Stephen Porges, PhD, in the mid ‘90s. The Polyvagal Institute describes PVT as ‘through the process of evolution the mammalian ANS [Autonomic Nervous System] has a primary repertoire of three principle states:’ ‘Relaxed,’ ‘Immobilised’ and ‘Mobilised.’ The theory emphasises the role of the Autonomic Nervous System (ANS), and in particular the vagus nerve, in regulating the behaviour of mammals, which it says is unique to mammals.

Professor Grossman and his co-authors refute five key premises of the PVT in the recent paper. He spoke to InSight+ from Germany.

“The base of the Polyvagal Theory is that there are two vagal areas in the brainstem: the dorsal vagus — the dorsal motor nucleus, in fact — and the ventral area, which is named the nucleus ambiguous,” said Professor Grossman.

“They do exist. And they do have different functions. But they’re not the functions that the PVT mainly attributes to them.”

“Particularly the dorsal vagus nucleus, which predominantly influences control of gut function. There is some influence upon heart rate, but it is usually small or very small in most species of mammals examined.”

“PVT confidently asserts quite the opposite, that the dorsal vagus can induce massive and even lethal heart-rate slowing under conditions of immobility due to extreme emotional circumstances (eg, emotional freezing and psychological dissociation).”

“There is absolutely no evidence to support this role of the dorsal vagus, and much to speak against the theory.”

“The ventral vagus nucleus ambiguus (NA), on the other hand, does, in fact, contributes to the how fast the heart beats. Increased vagal impulses to the heart, originating in the brainstem NA, serve to slow heart rate.”

“Under normal conditions, we cannot directly and noninvasively measure vagal activity to the heart, so researchers have relied upon a particular phenomenon to index cardia vagal activity indirectly. This phenomenon previously known as respiratory sinus arrhythmia has recently been renamed respiratory heart-rate variability (RHRV), in order more accurately to describe phenomenon. RHRV is characterized by quickening of heart rate during inspiration, and slowing of heart rate during expiration.” RHRV is almost only the only noninvasive index we have of vagal influences upon heart rate and is the linchpin to all vagal research relating the vagus nerve and psychological functioning.”

“However, RHRV is an imperfect index of the extent of vagal traffic from brain to heart; it’s an approximate measure of the vagal effects upon heart rate, and merely reflects vagal contributions to the coordination of phase of breathing and heart rate, that is, the variations of heart rate occurring from inspiration to expiration. As an index of overall ventral vagal influence upon the heart, RHVR is subject to many limitations. PVT, on the other hand, proposes that it is a direct measure of such brainstem ventral-vagal influences upon the heart, which is clearly false.”

“Additionally, PVT proposes that the dorsal vagus is an evolutionarily primitive, reptilian area of thr brainstem that turns on during emotionally defensive situations, such as extreme danger. It posits that the dorsal vagal nucleus is essentially responsible for shutting down the autonomic nervous system during emotional freezing and dissociation.” Once again, the ventral vagus is responsible for parasympathetic control of heart rate (including RHRV).”

“Additionally, there are several studies and a meta-analysis showing that during emotional freezing associated with psychological dissociation, there is typically very little or no change in heart rate, certainly not a massive decrease, as in bradycardia.”

Professor Grossman says that while emotional immobility (shutdown) and psychological dissociation occur and are genuine physiological events, the best evidence indicates those experiences are not regulated by the ANS alone, certainly not primarily by the dorsal vagus, but by various brain centres.

Lizards, mammals, and the ventral vagal

Another central idea of the PVT is that the mammalian ventral vagus is evolutionarily advanced, and dorsal vagus represents a ‘left-behind’ reptilian vagus.

“Porges himself used to talk about the “smart” and the “dumb” vagus in the 1990’s,” said Professor Grossman.

“PVT maintains that the ventral vagus in mammals has been “repurposed” to be responsible for positive, affiliative psychological processes including social regulation, safety and co-regulation. And that other vertebrates — for example fishes, reptiles, amphibians and birds — do not show complex social behaviours.”

“Reptiles, particularly, have been depicted as emotionally defensive animals, who primarily react to threat.”However, there is ample evidence of complex social behaviours in nonmammal vertebrates. There is no evidence that the ventral vagus has been repurposed in mammals to facilitate higher-level social processes.”

A career of sharing knowledge

Professor Grossman wrote his first major article on relations between psychological processes, breathing and  parasympathetic control of heart rate over 40 years ago, entitled “Breathing, Stress and Cardiovascular Function.

“My interest originally focussed upon trying to measure vagal influences on the heart. Early and later collaborations with expert physiologists led me to see what we do and do not know about the parasympathetic and autonomic nervous system in relationship to psychological processes, as well as the serious problems we have assessing vagal activity.”

“I understood quite early that my primary training as psychologist did not adequate prepare me to understand the complexities of autonomic physiology, and so I would need to communicate and to work with experts in that area.”

“This became very clear as I was preparing my first critiques of, and alternative to, PVT published in 2007, when I first sent emails to the very top evolutionary specialists I could find. I asked four of them for reprints of their papers, and whether they’d heard of the PVT and what they thought. Within 24 hours, all four wrote back that they considered the theory to be untenable.”

“One of the four was Edwin W. Taylor, certainly the most distinguished living scholar of ANS evolution, who then accepted my invitation to co-author of one of the 2007 publications.”

“As a result of my experiences, one of my primary motivations, when exploring mind-body relations, has long been to contribute to improved understanding between physiologists, on the one hand, and psychologists and other healthcare professionals, on the other. Otherwise, the danger exists that that those untrained in physiology may over-simplify and over-interpret the modest knowledge they do have regarding neurophysiological processes. This can easily lead to providing erroneous information to vulnerable patients.”

What about the therapies?

Professor Grossman’s conclusion is that psychologists, psychiatrists, psychotherapists and allied professionals currently influenced by PVT should reorient and consider other already existing, as well as novel, psychophysiological explanations to explain states related to psychological trauma or other disturbances.

“There’s a relatively sound psychophysiological literature that has more refined, more complex explanations for psychological or physiological responses to stress or emotional freezing,” said Professor Grossman.

“Additionally, although there are certainly physiological processes going on during these and other states, we may not be able to specify what those processes are for individual patients. In the end, we are all —patients and nonpatients — left with our lived experience of physical sensations and perceptions during stressful situations, for example, a sense of laboured breathing, a pounding heart, gut discomfort, sweating or muscle tension. We definitely cannot feel our vagus nerve nor know exactly what caused these symptoms. I, in fact, wonder whether that is important for patients, who often merely want their symptoms to be acknowledged as real.”

“Nonetheless, dismissing somatic therapies, or psychotherapy, is not the point. Many of these practices relate to our lived experiences of body and mind. They have also been around well before the PVT ever came into existence. For example, there are whole areas of meditation, yoga and relaxation practices, employed for millennia, which many have found helpful, without any accompanying autonomic explanation.”

Body of evidence

Professor Grossman continues to be inspired by working with groups of expert colleagues who provide one of the prime criteria for deciding on what is “scientific evidence.” “Remember that, siince the 1600s, when Robert Boyle first discovered the vacuum with a group of experts looking on, group agreement among experts has been a key cardinal principle for establishment of empirical evidence.”

“This paper is similar to the ones written in 2007 and 2023, but it has been notably improved by the contributions of the other authors, 38 true luminaries of autonomic nervous system scholarship. Regarding the level of accord, agreement among us was remarkably easy and fully unanimous.”

Becca Whitehead is a freelance journalist and health writer. She lives in Naarm and is a regular contributor to the MJA’s InSight+.

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