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 responses. The theory was introduced in 1994 by Stephen Porges. PVT is popular among some clinical practitioners and patients. 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 the brainstem branchiomotor nuclei and the visceromotor portion of the nucleus ambiguus. Evolutionary biologists consider the presence of myelinated vagus nerve fibers in lungfish leading from the nucleus ambiguus to the heart a contradiction of the theory's view of the mammalian nucleus ambiguus.

Polyvagal theory takes its name from the vagus nerve, a cranial nerve that forms the primary component of the parasympathetic nervous system. The traditional view of the autonomic nervous system presents a two-part system: the sympathetic nervous system, which is more activating ("fight or flight"), and the parasympathetic nervous system, which supports health, growth, and restoration ("rest and digest"). Polyvagal theory views the parasympathetic nervous system as being further split into two distinct branches: a "ventral vagal system" which supports social engagement, and a "dorsal vagal system" which supports immobilization behaviors, both "rest and digest" and defensive 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.