Polyvagal theory
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.
Polyvagal theory combines ideas from evolutionary biology and neurology, to claim that autonomic reactions have adapted to the phylogenetic development of neural circuits.
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, emotion, and social behaviour, are traditionally studied via peripheral indices of arousal such as heart rate, cortisol level and skin conductance.
[1] Polyvagal theory champions the measurement of vagal tone as a new index of stress vulnerability and reactivity, including in populations with affective disorders.
Polyvagal theory calls this the "vegetative vagus" because it sees it as being associated with primal survival strategies of primitive vertebrates, reptiles, and amphibians.
[17] Note: While the vagus nerve's role in downregulating the heart rate is well-established, the notion that a fight-or-flight response can be triggered without engaging the sympathetic nervous system is not substantiated by any evidence.
In order to maintain homeostasis, the central nervous system responds constantly, via neural feedback, to environmental cues.
[25] That is, RSA is proposed as a measurable, noninvasive way to see how the vagus modulates heart rate activity in response to stress.
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'.
[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."
[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.
Doody, Burghardt & Dinets [34] consider several ways of assessing and classifying animal sociality and state that "Porges’ dichotomy is incorrect.
Polyvagal theory proposes a relationship between RSA responses and forms of psychopathology, but a meta-analysis finds the empirical evidence to be inconclusive.
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.
