The Problems with The Polyvagal Theory

Maxwell Pearl, Ph.D.

Introduction

I fell in love with neurons and brains watching a presentation on neural networks in college.

During my junior year, I took a neuroscience course, and was awed and sometimes frustrated by the

complexity of how nervous systems worked, even the ones of simple animals. It’s been a long time since

my doctoral studies in neuroscience, and I’ve traveled a long way to become a teacher of mindfulness,

self-compassion and embodiment. But in those 35 years of time, I’m still, really, a neuroscientist at

heart, and I want the work that I do to be informed by what we know of the nervous system.

One of the most salient questions about how we work as human beings is how our minds and

bodies interact. We want to understand how they work together to help us handle danger, regulate our

emotions, and interact with each other socially. We want to understand why, for example, we

sometimes freeze when we get triggered, or fly into anger or fear. I continue to be interested in the

ways in which our body’s unconscious physiological responses are central to our emotional experience,

and I want to understand how our emotional experience can creating avenues for healing and regulation

of our emotional lives.

We know a lot about how our behavioral responses to danger and threat affect our minds and

bodies, and, importantly, how chronic stress can create long term physiological and psychological

effects. What we don’t know a lot about is the very specific mechanisms of these in our brains and

bodies.

Science, frankly, is complicated. It is littered with results, theories and laws that are later either

proven, revised, or debunked. Any solid scientific conclusions involve years of research by many

scientists. They involve many, sometimes conflicting primary research papers which can be difficult to
understand by most people who don’t work in the specific field in which they were written, let alone

non-scientists.

The study of human neuroscience is a particularly complex undertaking. Our ability to examine

and experiment on human beings is, for very good reasons, rather limited. So, our understandings of our

brains come from a wide variety of indirect avenues. We look at brains from deceased people, which

gives a once-in-time detailed anatomical snapshot but doesn’t tell us much about function. We study

animals of all sorts: from invertebrates to primates. The results of our research from animal studies have

no guarantees that we specifically function in the same exact way. We can confirm some animal studies

using behavioral and psychological research on humans, which can tell us a lot about behavior, but not a

lot about the brain. Brain imaging studies, especially the newer techniques, like functional MRI, or EEG

tomography, are helpful as well, but have a much lower resolution in terms of detailed brain structure

and activity than animal studies or anatomy of brains after death.

Stephen Porges’ Polyvagal Theory is a theory that has captured the interest of many people

outside of the field of social neuroscience. It tries to explain the ways in which our Peripheral Nervous

System (PNS) interacts with our Central Nervous System (CNS) in times of threat, stress, and social

engagement. It attempts to help us understand better how our responses to threat interrupt and

interact with our ability to engage with other human beings in social settings. It has been used in many

fields to provide a jumping off point for therapies relating to chronic stress, trauma, and dissociation. It’s

relatively simple to understand and seems to encompass our behavioral observations.

In the Polyvagal Theory there are three different hierarchical levels in the nervous system: The

Social Engagement System, the Sympathetic Nervous System, and the Parasympathetic Nervous system.

These systems act differently when “neuroception” has told us whether we are in a state of threat or

safety. In a state of threat, we first try the Social Engagement System: negotiation, appeasement, etc. If

that doesn’t work, we move to fight or flight via the Sympathetic Nervous System. If the situation
becomes life threatening, we move to freeze – immobilization, faint, etc. via the Parasympathetic. If we

are in a state of safety, our Sympathetic system allows for mobilization – dancing, sport, etc., and our

Parasympathetic allows for rest and sleep. In the safe state, our Social Engagement system allows for

play, sexuality, etc. There are underlying evolutionary, neuroanatomical and neurophysiological

suppositions to this larger hierarchal framework.

This larger hierarchical framework isn’t really in a form that neuroscience can validate

experimentally, but the underlying suppositions are. Scientifically, the Polyvagal Theory isn’t

experimentally verified, and doesn’t really help to explain anything we hadn’t already been able to

understand. It both oversimplifies and overemphasizes the role of the vagus nerve in terms of its

involvement in threat and social engagement. There is evidence against many of its core suppositions.

There have been critiques of the Polyvagal Theory in the neuroscience literature for many years, but

these have not made their way out of that field into the open. Here are a few of the most important of

those critiques.

“Polyvagal = Bivagal” and evolutionary age

The term “Polyvagal” is a misnomer, although “poly” does sound sexier than “bi”. There are

only two efferent (that is, moving outward from the central nervous system (CNS) to the body, effecting

what happens in the body) systems: dorsal (back) and ventral (front). In Polyvagal Theory (PVT), the

dorsal, unmyelinated (slow), system emerges from the dorsal motor nucleus (part of the medulla,

located in the brain stem) of the vagus, which is largely responsible for gut innervation. Porges’ PVT

associates this system, supposedly evolutionarily older, with immobilization and dissociation

(freeze/faint.)

The second efferent system is the myelinated (fast) ventral vagus, which is supposed to be

evolutionarily newer, and has the ability to down-regulate immobilization as well as fight/flight
responses. It is associated with the nucleus ambiguous (also in the medulla). In PVT, it regulates the

heart and lungs, and allows for social engagement, down-regulating in “safe” environments.

A core supposition of Polyvagal Theory is that there is a phylogenetic (that is, evolutionary) shift

between reptiles, who only use the “older” dorsa vagus, and mammals, who use the “newer” ventral

vagus in addition, which allows for a “face-heart” connection that is involved in social engagement, and

allows social interactions, environment, and visceral state to influence one another.

The problem is, there is no evidence of this evolutionary (phylogenetic) shift. You find myelinated

ventral vagus nerves in cartilaginous fish (like lungfish and sharks), which are evolutionarily older than

reptiles.

The nucleus ambiguus is ambiguous

In PVT, responses to the environment fall into three categories: life-threatening, danger, and

safety. And they are related to the social engagement system, allowing for facial expressions, vocal

expression, etc. – inhibiting them when the environment is dangerous or life-threatening, disinhibiting

them when the environment is safe. The nucleus ambiguus, where the “phylogenetically newer” (not

correct, as explained above) ventral vagus originates, does have cardioinhibitory neurons (for down-

regulation of fight/flight,) and also does have neurons for laryngeal, pharyngeal and esophageal muscles

(for vocalization, etc.) but does not control facial expression nor hearing. The facial nucleus, which does

control facial expression, does not affect the nucleus ambiguus.

Other cranial nerves have more to do with coordination and control of the facial muscles than

the vagus nerve.

The dorsal vagus doesn’t do bradycardia

originates, downregulates fight/flight by slowing the heart rate (technically known as bradychardia.) For

a long time, bradychardia has been known not to be affected by the dorsal motor nucleus under any but

the most extreme conditions (and even in that case, there is little evidence and a lot of doubt.)

Neuroception isn’t simple

An important part of the Polyvagal Theory is the idea that we evaluate our environment, and

determine whether it is safe, dangerous, or life threatening via a process called “neuroception”.

Neuroception is defined in PVT as “…a neural process that enables humans and other mammals to

engage in social behaviors by distinguishing safe from dangerous contexts.”

The problem is, “neuroception” is very complex, and involves several categories of psychological

phenomena, including fear, threat perception, social behavior, and emotional regulation. Each of these

has been studied in some depth by many researchers, and a large number of brain structures unrelated

to the vagus nerve are known to be involved. PVT does not explain any of these with any precision.

Conclusion

There are other neuroanatomical and neurophysiological critiques of PVT, but I won’t detail

them here, as they are not so easy to explain. Basically, the most important core suppositions of the

Polyvagal Theory don’t seem to have much in the way of evidence to support them, and a fair bit of

evidence against them. Further, PVT doesn’t help to explain what we didn’t already know, in a scientific

(psychological or neuroscientific) sense.

One of the things that is great about science is that it does, in very clear methodical ways, help

us understand the world. However, it is not simple, and it takes a lot of work to translate what scientists
do and know to folks who aren’t scientists. I can understand why the Polyvagal Theory has become so

popular in non-scientific circles, even though most neuroscientists dismiss it.

The basic framework of the Polyvagal Theory, describing differences in our physiological

responses and availability of behavior based on perception of threat, and that chronic activation of our

threat system leads to psychological and physiological damage and harm, is important and useful for

therapeutic applications and embodiment work. But none of that was particularly new to PVT – the

understanding of those have been around for a while. The Polyvagal theory did have a way of tying it all

together in a neat, relatively easy to understand bow. But that bow doesn’t have any scientific

foundation.

The problem with this is that it means that there are things we’ll miss if we take Polyvagal

Theory as The Way Things Are. Avenues of understanding we might not embark on, questions we won’t

ask, different theories that are harder to understand but more scientifically valid (there actually is at

least one) will be dismissed, or at least not talked about in therapeutic or embodiment circles. We don’t

always need (and will not always find) neuroscientific evidence for why certain therapies or

embodiment practices work. But we shouldn’t let theories with scientific evidence against them drive

the way we think about our brains. This is complex stuff, and we have to be willing to embrace the

complexity and understand that there may never be a theory that neatly ties this together, because

human brains are messy, and understanding human brains is even messier.