THE VAGUS NERVE

The Master Regulator Between Brain, Gut, and Immunity.

The vagus nerve — the tenth cranial nerve — is the primary conduit of the parasympathetic nervous system, carrying signals bidirectionally between the brain and the heart, lungs, gut, and immune system. It is the biological highway of the gut-brain axis, transmitting the microbiome's chemical signals directly to the brain and governing inflammation via the inflammatory reflex. Vagal tone — a measure of the nerve's functional strength — is directly correlated with resilience to stress, speed of immune resolution, heart rate variability, and capacity for social connection. Chronic stress, trauma, poor diet, and toxin exposure all systematically degrade vagal tone.