What the Gut-Brain Axis Actually Is Buried in the lining of your digestive tract is an independent network of roughly 100 to 500 million neurons — the enteric nervous system. It communicates constantly with your brain, primarily through the vagus nerve, a long, wandering nerve that runs from your brainstem all the way down to your colon. This connection carries signals in both directions: the brain sends instructions to the gut, and the gut sends signals back up to the brain.