Modern neuroscience is now discovering the anatomy underlying Whitman's poetry. It has taken his poetic hypothesis--the idea that feelings begin in the flesh--and found the exact nerves and brain regions that make it true. Antonio Damasio, a neuroscientist who has done extensive work on the etiology of feeling, calls this process the body loop. In his view, the mind stalks the flesh; from our muscles we steal our moods.
How does the brain generate our metaphysical feelings from the physical body? According to Damasio, after an "emotive stimulus" (such as a bear) is seen, the brain automatically triggers a wave of changes in the "physical viscera," as the body prepares for action. The heart begins to pound, arteries dilate, the intestines contract, the adrenaline pours into the bloodstream. These bodily changes are then detected by the cortex, which connects them to the scary sensation that caused the changes in the first place. The resulting mental image—an emulsion of thought and flesh, body and soul—is what we feel. It is an idea that has passed through the vessel of the body.
Over the course of his distinguished career, Damasio has chronicled the lives of patients whose brains have been injured and who, as a result, are missing this intricate body-brain connection. Although they maintain full sensory awareness, these patients are unable to translate their sensations into emotions. The pounding of the heart never becomes a feeling of fear. Because the mind is divorced from the flesh, the patient lives in a cocoon of numbness—numb even to his or her own tragedy.