Chapter Nine — The Autonomic Story: Polyvagal Theory and What the Evidence Supports

Chapter Nine.

The Autonomic Story: Polyvagal Theory and What the Evidence Supports.

The practices can be sound even when the story explaining them is disputed. It is worth knowing which is which.

"The body keeps its own counsel, and it is usually trying to help."

Nerve does not yet know

which story explains it best —

still, the exhale works.

Polyvagal theory has been enormously influential in trauma-informed practice, and it appears in nearly every popular account of ADHD and emotional overwhelm — including the first edition of this book, where it was presented as settled science. It is not settled. This chapter tells you what the theory claims, what is contested, and what remains usable regardless of how the dispute resolves.

What the theory claims.

Polyvagal theory proposes that the autonomic nervous system is organised into three hierarchically ordered states with distinct evolutionary origins and distinct vagal pathways: a ventral vagal state associated with social engagement and felt safety, a sympathetic state of mobilisation, and a dorsal vagal state of shutdown or immobilisation. It further proposes that respiratory sinus arrhythmia can serve as an index of ventral vagal tone, and it introduced neuroception — subcortical appraisal of safety and threat below conscious awareness.

What is contested.

In 2023 Grossman published a systematic critique in Biological Psychology arguing that all five foundational premises of the theory are inconsistent with current neurophysiology — including the proposed functional division between vagal nuclei and the use of respiratory sinus arrhythmia as a general index of vagal tone. In 2026 a multi-authored paper co-signed by a large group of autonomic researchers argued in Clinical Neuropsychiatry that the theory is untenable as stated. Porges published a detailed rebuttal in the same journal, arguing that the critique engages a reconstructed version of the theory rather than its peer-reviewed formulation. At the time of writing, the dispute is live and unresolved.

What does this mean for you, sitting with a nervous system that plainly does something dramatic when a message arrives? Less than you might fear. The observations the theory organises are not in dispute: people shift between mobilised, shut down, and settled states; those shifts are involuntary and fast; safety cues from other people change them measurably; and slow breathing changes subjective arousal and heart-rate variability. What is disputed is the anatomical and evolutionary explanation. A practice is not invalidated when its rationale is revised — but you are entitled to know that the rationale is under revision, rather than being handed a certainty that does not exist.

What holds, whatever happens to the theory.

Interoception is real and trainable. The perception of internal bodily state is supported by identified neural substrates, and interoceptive accuracy is distinguishable from interoceptive awareness — the two correlate only modestly, which is why noticing that you are activated is a separate skill from being right about it. Body-scan practice trains the second.

Co-regulation is real. Whatever the mechanism, another person's calm voice, unhurried pace, and steady face change your state. This is why the tone of a clinician matters more than the technique, and why one steady friend outperforms an hour of self-talk.

Slow breathing helps many people, measurably. Use it. Describe it accurately: "this settles me," not "this activates my ventral vagal complex."

State-dependent capability is a useful clinical fact. What you can do at intensity two and intensity eight are different lists. Plan for both. The window-of-tolerance metaphor remains a helpful description even though it is a metaphor and not a measurement.

Evidence at a glance.

Well supported: Interoception as a neurally grounded, measurable capacity with distinguishable components.

Moderately supported: Mindfulness and body-awareness training in adult ADHD.

Clinical model: Polyvagal theory's core physiological premises — actively contested in the peer-reviewed literature.

Clinical model: The window of tolerance — clinical metaphor, not a measured construct.

Bringing This to Your Clinician.

If you have found real relief using polyvagal language ("I was in shutdown"), you do not need to abandon it. It is worth knowing — and saying to your clinician if it comes up — that the underlying theory is scientifically contested; what you can rely on is the practice's effect on you, described in your own words, rather than the mechanism behind it.