The second brain

In 1998 a Columbia University physician named Michael Gershon published a book with a title that sounded like a metaphor and wasn't: The Second Brain. The gut, he showed, has its own nervous system, the enteric nervous system, with about five hundred million neurons, more than the spinal cord, that can run digestion entirely on its own. It makes most of the body's serotonin. And it's connected to the brain in the head by the vagus nerve, which carries far more traffic up from the gut than down to it.

That last fact is the key. The gut talks to the brain constantly, and the brain listens. The phrases we use, gut feeling, butterflies, can't stomach it, sick with worry, are not figures of speech. They're reports from the second brain, delivered up the vagus, and they shape mood, judgment and stress in ways the research is only now measuring. The microbiome from two days ago is part of the conversation: the bacteria produce compounds the gut's neurons respond to, and the whole system, microbes, gut, vagus, brain, is now called the gut-brain axis.

It's a Healing key because so many of the wounds this chamber has been honoring are stored, as the body-therapy keys said, below the neck. Gershon put anatomy under that claim. The knot in the stomach before the hard conversation is five hundred million neurons doing their job.

And it's a practical key. What settles the gut settles the mind: slow eating, fiber, fermented foods, the long exhale that stimulates the vagus, which you've been practicing since the second month. Chronic gut trouble is a physician's door, and so is anything that's lasted more than a few weeks. The daily conversation with the second brain is yours.