The vagus nerve, the main nerve in the rest-and-digest nervous system, links the brain stem, voice box, lungs, heart, pancreas and gut. In total, 80 percent of its fibers carry information back to the brain, mostly from the heart and gut. The enteric nervous system, often called the second brain, is an independent nervous system controlling digestion. The brain in the gut and the brain in the head communicate and cooperate (and occasionally disagree) largely by means of the vagus nerve.
