“A purely disembodied human emotion is a nonentity,” William James wrote in his pioneering 1884 theory of how our bodies affect our feelings — the first great gauntlet thrown at the Cartesian dualism of body versus mind. In the century and a half since, we have come to see how the body and the mind converge in the healing of trauma ; we have come to see consciousness itself as a full-body phenomenon .

Beyond the brain, no portion of the body shapes our mental and emotional landscape more profoundly than the tenth cranial nerve — the longest nerve of the autonomic nervous system that unconsciously governs the inner workings of the body.…