Polyvagal theory (PVT) is a collection of proposed evolutionary, neuroscientific, and psychological constructs pertaining to the role of thevagus nerve in emotion regulation, social connection, and fear responses. The theory was introduced in 1994 byStephen Porges.[1] PVT is popular among some clinical practitioners and patients.[2] However, multiple aspects of the theory are widely criticized for being at odds with known science. For example,neuroanatomists point out that the theory is incorrect in claiming direct communication between thebrainstembranchiomotor nuclei and the visceromotor portion of thenucleus ambiguus.[3]Evolutionary biologists consider the presence ofmyelinated vagus nerve fibers inlungfish leading from the nucleus ambiguus to the heart a contradiction of the theory's view of the mammalian nucleus ambiguus.[4]
Polyvagal theory takes its name from the vagus nerve, acranial nerve that forms the primary component of the parasympatheticnervous system.[5][6][7] The traditional view of theautonomic nervous system presents a two-part system: thesympathetic nervous system, which is more activating ("fight or flight"), and theparasympathetic nervous system, which supports health, growth, and restoration ("rest and digest").[8] Polyvagal theory views the parasympathetic nervous system as being further split into two distinct branches: a "ventral vagal system" which supportssocial engagement, and a "dorsal vagal system" which supports immobilization behaviors, both "rest and digest" anddefensive immobilization or "shutdown". This "social engagement system" is a hybrid state of activation and calming that plays a role in the ability to socially engage.[9]
Thevagus, or tenthcranial nerve, is a primary component of theautonomic nervous system, which operates the internal organs. It transmitsparasympathetic signals to and from the heart, lungs, and digestive tract.[10] The vagal system is claimed to be inhibitory of primal instincts by being part of theparasympathetic nervous system, in opposition to thesympathetic-adrenal system, involved in mobilization behaviors.[9]
Polyvagal theory was developed in 1994 by Porges, who at the time was director of the Brain-Body Center at theUniversity of Illinois at Chicago.[11] It focuses on the structure and function of the two efferent branches of the vagus cranial nerve, which originate from themedulla.[12] Each branch is claimed to be associated with a different adaptive behavioral strategy; the ventral branches more restful in nature and the dorsal ones more active in nature.[13]
According to the theory, three organizational principles can be distinguished:[vague]
Porges describes the three neural circuits as regulators for reactive behavior. His findings were taken into account by some theorists ofchildhood trauma, with related techniques used by trauma therapists such asBessel van der Kolk,[16]Peter A. Levine and Marianne Bentzen.
Polyvagal theory combines ideas fromevolutionary biology and neurology, to claim that autonomic reactions have adapted to the phylogenetic development ofneural circuits.[9] It claims that the sympathetic nervous system, and two distinct branches of the parasympathetic nervous system, arephylogenetically ordered and activated for responses.[12] The branches of the vagal nerve are claimed to serve different evolutionarystress responses in mammals: the more primitive branch is said to elicit immobilization behaviors (e.g., feigning death), whereas the more evolved branch is said to be linked to social communication and self-soothing behaviors.[17] These functions are claimed to follow aphylogenetic hierarchy, where the most primitive systems are activated only when the more evolved functions fail.[9]
According to the theory, these neural pathways regulate autonomic states and the expression of emotional and social behaviour. It claims that in mammals, facial expressions are connected to internal physical reactions, such as cardiac and digestive changes,[17] and in general physiological state dictates the range of behaviour and psychological experience.[9]
Claims about the nature of stress,emotion, andsocial behaviour, are traditionally studied via peripheral indices of arousal such asheart rate,cortisol level and skin conductance.[1] Polyvagal theory champions the measurement ofvagal tone as a new index of stress vulnerability and reactivity, including in populations withaffective disorders.[18]
The dorsal branch of the vagus nerve originates in thedorsal motor nucleus and is postulated by polyvagal theory to be the phylogenetically older branch.[1] This branch isunmyelinated and exists in most vertebrates. Polyvagal theory calls this the "vegetative vagus" because it sees it as being associated with primal survival strategies of primitive vertebrates, reptiles, and amphibians.[19] Under certain conditions, these animals "freeze" when threatened, conserving their metabolic resources. This draws on the simplifying claims of thetriune brain theory which are no longer considered accurate due to the many exceptions to this rule (seeTriune brain § Status of the model).[1]
The DVC provides primary control of subdiaphragmatic visceral organs, such as the digestive tract. Under normal conditions, the DVC maintains regulation of these digestive processes. However, prolonged disinhibition can be lethal for mammals, as it results inapnea andbradycardia.[12][dubious –discuss]
With increased neural complexity as seen in mammals (due to phylogenetic development) there is said to have evolved a more sophisticated system to enrich behavioral and affective responses to an increasingly complex environment.[12][dubious –discuss] The ventral branch of the vagus originates in thenucleus ambiguus and is myelinated to provide more speed in responding.[12] Polyvagal theory calls this the "smart vagus" because it associates it with the regulation of sympathetic "fight or flight" behaviors by way of social affiliative behaviors.[19] These behaviors are said to include social communication and self-soothing and calming.[12] In other words, this branch of the vagus is said to inhibit or disinhibit defensivelimbic circuits, depending on the situation. Note: Attributing defensive behaviours purely to the limbic system is anoversimplification, as these are triggered by perceived threats, thus requiring an interplay of brain areas performing sensory integration, memory, and semantic knowledge with the limbic system to be elicited. Similarly, theregulation of emotions requires a complex interplay of higher cognitive areas with limbic ones.The vagus nerve mediates the control of supradiaphragmatic visceral organs, such as the esophagus, bronchi, pharynx, and larynx. It also exerts an important influence on the heart. When vagal tone to the heart'spacemaker is high, a baseline or resting heart rate is produced. In other words, the vagus acts as a restraint, or brake, limiting heart rate. However, when vagal tone is removed, there is little inhibition to the pacemaker, and according to polyvagal theory, rapid mobilization ("fight/flight") can be activated in times of stress, but without having to engage the sympathetic-adrenal system, as activation comes at a severe biological cost.[12] Note: While the vagus nerve's role in downregulating the heart rate is well-established, the notion that afight-or-flight response can be triggered without engaging the sympathetic nervous system is not substantiated by any evidence.
In order to maintainhomeostasis, thecentral nervous system responds constantly, via neural feedback, to environmental cues.[8] Stressful events disrupt the rhythmic structure of autonomic states, and subsequently, behaviors.[8] Since the vagus plays such an integral role in theperipheral nervous system via regulation of heart rate, Porges suggests that the amplitude ofrespiratory sinus arrhythmia (RSA) is a good index of parasympathetic nervous system activity via the cardiac vagus.[20] That is, RSA is proposed as a measurable, noninvasive way to see how the vagus modulates heart rate activity in response to stress. If true, this method could be useful to measure individual differences in stress reactivity.[21]
RSA is the widely used measure of the amplitude of heart rate rhythm associated with the rate of spontaneous breathing.[20] Research has shown that amplitude of RSA is an accurate indicator of theefferent influence of the vagus on the heart.[20] Since inhibitory effects of the VVC branch of the vagus allow for a wide range of adaptive, prosocial behaviors, it has been theorized that individuals with greater vagal tone are able to exhibit a greater range of such behaviors. On the other hand, decreased vagal tone is associated with illnesses and medical complications that compromise the CNS.[20] These complications may reduce one's capacity to respond to stress appropriately.
Healthy human fetuses have high variability in heart rate, which is mediated by the vagus.[22] On the other hand, heart rate decelerations, which are also mediated by the vagus, are a sign offetal distress. More specifically, prolonged withdrawal of vagal influence on the heart creates a physiological vulnerability to the influence of the dorsal vagal complex, which in turn producesbradycardia (very low heart rate). However, the onset of this deceleration is commonly preceded by transitorytachycardia, which is reflective of the immediate effects of ventral vagal complex withdrawal.[23]
A 2024 review inDevelopmental Psychobiology analyzed polyvagal theory's neurobiological aspects in light of 25 years of research, examining both strengths and limitations through evidence from comparative anatomy, embryology, epigenetics, and neuroscience.[24] A 2022 review in the Japanese journalBrain and Nerve described the theory's potential applications in psychotherapy, particularly regarding trauma pathophysiology and the role of social interaction in treatment.[25]
In a 2021 publication, Porges stated that "the theory was not proposed to be either 'proven' or 'falsified', rather to be informed by research and modified".[26] Falsifiability is a central tenet of thescientific method.
In a 2023 review of the literature, Paul Grossman lists five premises of polyvagal theory and states that "there is broad consensus among experts [...] that each basic physiological assumption of the polyvagal theory is untenable. Much of the existing evidence, upon which these consensuses are grounded, strongly indicates that the underlying polyvagal hypotheses have been falsified."[27]
Although proponents likeBessel van der Kolk praise the theory's explanatory power,[16] Grossman considers the explanations offered by the theory unsubstantiated.[28]
In a 2025 paper inClinical Neuropsychiatry, Porges responded to these critiques, stating that "contrary to claims that Polyvagal Theory lacks falsifiability, the theory has generated a range of specific, testable predictions," including hierarchical recruitment of autonomic states under threat, the influence of social cues on vagal tone, and the effects of acoustic interventions on emotion regulation.[29] Porges characterized the critiques by Grossman and Taylor as "misrepresentations" that "overlook the hierarchical structure of the autonomic nervous system or misunderstand the role of neuroception in mediating physiological state shifts."[29]
Neuhuber and Berthoud (2022) state that polyvagal theory's "basic phylogenetic and functional-anatomical tenets do not withstand closer scrutiny".[3] They argue that polyvagal theory incorrectly portrays the role of the different vagal nuclei in mediating the freeze response. According to their analysis, the evidence "does not support a role of the 'dorsal vagal complex' in freezing as proposed by the PVT" and the dorsal vagal complex "should not be linked to passive defensive behavior".Regarding the proposed "ventral vagal complex", they state that "the PVT, by construeing a 'new ventral vagal complex' encompassing the entire branchiomotor column ascribed to the vagus much more than it actually can serve." They see it as "misleading to propose that brainstem branchiomotor ('source') nuclei 'communicate directly with the visceromotor portion of the nucleus ambiguus'", and conclude that the relevant networks "should not be termed 'ventral vagal complex'. This terminology may insinuate that the vagus is a "prime mover". This not the case [...]".
Taylor, Wang & Leite (2022) similarly regard it as "invalid to refer to this as a 'vagal system' or to postulate the existence of a 'smart vagus'."[30]
Grossman and Taylor (2007) argue that there is no evidence that the dorsal motor nucleus (DMN) is an evolutionarily more primitive center of the brainstem parasympathetic system than the nucleus ambiguus (NA), and review evidence to the contrary.[28]
A more recent paper by Monteiro et al. (2018) finding myelinated vagus nerve fibers oflungfish leading from the nucleus ambiguus to the heart also indicates that polyvagal theory's hypothesis that the nucleus ambiguus is unique to mammals is incorrect.[4] They state that "the mechanisms [Porges] identifies as solely mammalian are undeniably present in the lungfish that sits at the evolutionary base of the air-breathing vertebrates."
Grossman (2023) concurs, stating that "the polyvagal notion that the ventral vagal area is unique to mammals is opposed by years of evidence" and that the "findings, as a whole, firmly and consistently contradict the polyvagal hypotheses that propose the [dorsal vagal motor nucleus] as the "source nucleus" of unmyelinated pathways and the [nucleus ambiguus] as the "source nucleus" of myelinated pathways in mammals".[27]
Results reviewed by Taylor, Leite and Skovgaard (2010) also "refute the proposition that centrally controlled cardiorespiratory coupling is restricted to mammals, as propounded by the polyvagal theory of Porges".[31]In Taylor, Wang & Leite's 2022 review, the evidence for the presence of cardio-respiratory interactions similar to respiratory sinus arrhythmia (RSA) and their potential purpose in blood oxygenation in many vertebrate species (both air- and water-breathing) leads them to conclude that RSA may be a relic of older cardio-respiratory systems, contrary to polyvagal assumptions.[30]
The dichotomy between asocial reptiles and social mammals subscribed to by polyvagal theory has been contested. Doody, Burghardt & Dinets[32] consider several ways of assessing and classifying animal sociality and state that "Porges' dichotomy is incorrect. While many mammals (particularly humans) may show more complex social behavior than reptiles, there is considerable overlap in social tendencies between the two groups. The labels 'social' and 'asocial' are too crude to have utility in a comparative framework of social behavior and should not be used to describe taxa". Listing examples of social behavior in reptiles and other non-mammal vertebrates, they observe that "PT appears to rest upon 20th century folk interpretation of vertebrate evolutionary biology rather than on current scientific understanding of it."
Polyvagal theory proposes a relationship between RSA responses and forms of psychopathology, but a meta-analysis finds the empirical evidence to be inconclusive.[33]
According to Grossman and Taylor,[28] the existing research indicates that respiratory sinus arrhythmia is not a reliable marker of vagal tone, since it is subject to both respiratory variables and sympathetic (beta-adrenergic) influences in addition to vagal influences. In addition, they argue that the results of Porges' 2003 study on two species of lizard was flawed due to incorrect measurements of heart rate variability.
Reviewing more recent evidence, Paul Grossman again finds RSA not "a direct measure of cardiac vagal tone" due to confounding factors. In addition, he concludes that contrary to polyvagal claims "there is no credible evidence that the [dorsal vagal motor nucleus] plays any role in massive bradycardia", and that it "appears to have almost no effect upon vagal heart rate responses".[27] In a 2025 paper inClinical Neuropsychiatry, Porges responded to these critiques, stating that "contrary to claims that Polyvagal Theory lacks falsifiability, the theory has generated a range of specific, testable predictions," including hierarchical recruitment of autonomic states under threat, the influence of social cues on vagal tone, and the effects of acoustic interventions on emotion regulation.[29] Porges characterized the critiques by Grossman and Taylor as "misrepresentations" that "overlook the hierarchical structure of the autonomic nervous system or misunderstand the role of neuroception in mediating physiological state shifts."[29]
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