Polyvagal theory

Polyvagal theory is a set of ideas about the autonomic nervous system (the body's automatic regulator of heart rate, breathing, and digestion) proposed by neuroscientist Stephen Porges in 1994 and 1995. The theory suggests that the vagus nerve (the tenth cranial nerve, running from the brainstem to the heart, lungs, and gut) has two distinct branches in mammals: an older dorsal vagal pathway, proposed to govern immobilisation responses, and a newer myelinated ventral vagal pathway, proposed to support calm states and social engagement. A third element of the theory is "neuroception": a proposed process by which the nervous system unconsciously scans the environment for cues of safety or threat before conscious awareness registers them. Together, these circuits are said to create a hierarchy of responses, from social engagement, to fight-or-flight, to shutdown or freeze.¹

The theory has become influential in trauma therapy and somatic practice. At the same time, several of its core anatomical and evolutionary claims are contested in the comparative physiology and neuroscience literature. Critics argue that key premises, including the claimed distinction between dorsal and ventral vagal circuits and the evolutionary narrative about myelinated vagal fibres in mammals, are not supported by current neurophysiological evidence.²

The theory proposes a hierarchy of physiological states governed by which vagal circuit is active at any moment. In perceived safety, the myelinated ventral vagal pathway acts as a "brake" on the heart, allowing calm, flexible responses and social engagement. When the nervous system registers threat, that brake releases and the sympathetic nervous system drives fight-or-flight responses (raised heart rate, mobilisation). Under extreme or inescapable threat, the theory says the older dorsal vagal pathway produces a shutdown or freeze response. This proposed hierarchy, and the idea that felt safety is a physiological prerequisite for social connection, has been widely adopted in trauma and somatic therapies. Its influence in clinical settings is real and widely documented. However, its empirical foundations are disputed. A 2026 evaluation by Grossman and 38 co-authors from neuroscience and physiology concluded that the theory's major tenets are not supported by past or current knowledge, and that its core premises are not defensible based on existing neurophysiological and evolutionary evidence.³ Polyvagal theory remains a hypothesis: influential in practice and contested in the research literature.