Polyvagal theory
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Polyvagal theory (PVT) is a collection of proposed evolutionary, neuroscientific, and psychological constructs pertaining to the role of the vagus nerve in emotion regulation, social connection and fear response. The theory was introduced in 1994 by Stephen Porges.[1] There is consensus among experts that the assumptions of the polyvagal theory are untenable.[2] PVT is popular among some clinical practitioners and patients,[3] but it is not endorsed by current social neuroscience.[4][5][6][7][8][9]
Polyvagal theory takes its name from the vagus, a
Theory
The
Polyvagal theory was developed in 1994 by Porges, who at the time was director of the Brain-Body Center at the
According to the theory, three organizational principles can be distinguished:[vague]
- Hierarchy: The autonomic nervous system reacts in three reaction patterns, which are activated in a specific order.
- Neuroception: In contrast to perception, it is here a cognition without awareness, triggered by a stimulus such as danger.[14][19]
- Co-regulation: The need to feel safe enough to allow oneself to be in relationships, which is difficult for traumatized people.[20]
Porges describes the three neural circuits as regulators for reactive behavior. His findings were taken into account by some theorists of
Anatomical hypothesis
Polyvagal theory combines ideas from
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,[22] and in general physiological state dictates the range of behaviour and psychological experience.[14]
Claims about the nature of stress,
Proposed dorsal vagal complex (DVC)
The dorsal branch of the vagus nerve originates in the
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 in apnea and bradycardia.[17][dubious ]
Proposed ventral vagal complex (VVC)
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.
Vagal tone as a marker of stress
In order to maintain
RSA is the widely used measure of the amplitude of heart rate rhythm associated with the rate of spontaneous breathing.[25] Research has shown that amplitude of RSA is an accurate indicator of the efferent influence of the vagus on the heart.[25] 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.[25] These complications may reduce one's capacity to respond to stress appropriately.
Clinical applications in the human fetus
Healthy human fetuses have high variability in heart rate, which is mediated by the vagus.[27] On the other hand, heart rate decelerations, which are also mediated by the vagus, are a sign of fetal 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 produces bradycardia (very low heart rate). However, the onset of this deceleration is commonly preceded by transitory tachycardia, which is reflective of the immediate effects of Ventral Vagal Complex withdrawal.[28]
Reception
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."[2]
Although proponents like Bessel van der Kolk praise the theory's explanatory power,[21] Grossman considers the theory an unnecessary and unsubstantiated conflict imposed on the public dialogue.[29]
Neuroscientific claims
Neuhuber and Berthoud (2022) state that polyvagal theory's "basic phylogenetic and functional-anatomical tenets do not withstand closer scrutiny".[30] 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'."[31]
Evolutionary claims
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.[29]
A more recent paper by Monteiro et al. (2018) finding myelinated vagus nerve fibers of lungfish 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.[32] 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".[2]
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".[33] 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.[31]
The dichotomy between asocial reptiles and social mammals subscribed to by polyvagal theory has been contested. Doody, Burghardt & Dinets [34] 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."
Claims regarding cardiac functioning
Polyvagal theory proposes a relationship between RSA responses and forms of psychopathology, but a meta-analysis finds the empirical evidence to be inconclusive.[35]
According to Grossman and Taylor,[29] 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".[2]
Scientific standards
In a 2021 publication, Porges stated that "the theory was not proposed to be either proven or falsified".[36] Falsifiability is a central tenet of the scientific method.
See also
- Popular psychology
- Fringe science
- Emotional dysregulation
- Fight-or-flight response
- Freezing behavior
- Tend and befriend
- Autonomic nervous system
References
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- ^ "Polyvagal theory in practice". Counseling Today. 2016-06-27. Retrieved 2020-10-31.
- ISBN 978-0-19-972406-2.[page needed]
- ISBN 978-1-317-43918-9.[page needed]
- ISBN 978-0-674-72897-4.[page needed] Litfin, Karen T.; Berntson, Gary G. (2006). Social Neuroscience: People Thinking about Thinking People. MIT Press.ISBN 978-0-262-03335-0.[page needed]
- ISBN 978-0-19-969297-2.[page needed]
- ISBN 978-0-691-16727-5.[page needed]
- ISBN 978-0-19-534216-1.[page needed]
- ^ Anthony, Andrew. "Stephen Porges: 'Survivors are blamed because they don't fight'". The Guardian. Retrieved 2021-09-17.
- ISSN 0362-4331. Retrieved 2021-09-17.
- ISSN 0017-8012. Retrieved 2021-09-19.
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- ^ Essex, Tori (14 July 2021). "New Episode of Transforming Trauma: The Rhythm of Regulation: Exploring the Polyvagal Theory with Deb Dana". PACEsConnection.com. Retrieved 2022-01-21.
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Further reading
- Ulrich F. Lanius, Sandra L. Paulsen, Frank M. Corrigan: Neurobiology and Treatment of Traumatic Dissociation: Towards an Embodied Self. Springer Publishing Co., 2014
- Porges, S. W. (2006). "The Polyvagal Perspective". Biological Psychology. 74 (2): 116–143. PMID 17049418. (Review).
- Holly Bridges: Reframe Your Thinking Around Autism: How the Polyvagal Theory and Brain Plasticity Help Us Make Sense of Autism ISBN 978-1849056724 Jessica Kingsley Publishers. 2015
- Robert Bright: The Polyvagal Theory: The Simplified Guide to Understanding the Autonomic Nervous System and the Healing Power of the Vagus Nerve – Learn to Manage Emotional Stress and PTSD Through Neurobiology. White Publishing, Ltd., 2020, ISBN 978-1801119689
External links
- The Polyvagal Theory – www.wam.umd.edu
- After 20 years of "polyvagal" hypotheses, is there any direct evidence for the first 3 premises that form the foundation of the polyvagal conjectures? Paul Grossman, University Hospital of Basle, Switzerland, on ResearchGate, with references and some discussion starting January 2016
- Dunning, Brian (25 January 2022). "Skeptoid #816: The Dark Side of Polyvagal Theory". Skeptoid.