Your Second Brain

The wall of your gut holds its own nervous system — about 500 million neurons, more than your entire spinal cord. It runs digestion on its own and keeps working even if the vagus nerve is cut. That is why scientists call it your second brain.

It even speaks the brain's language, using the same chemical messengers: dopamine, serotonin, GABA, and dozens more. In fact, most of your body's serotonin is made down here. So the butterflies before a big talk and the sinking feeling of bad news are this second brain reacting in real time.