In a conversation with the editorial board of the Chicago Tribune on Tuesday, Homeland Security Chief Michael Chertoff said he thought there was an increased risk of the country coming under terrorist attack this summer—speculation he attributed to "a gut feeling." President Bush has also been known to turn to his digestive organ for advice: Explaining the Iraq invasion a few years ago, he told Washington Post reporter Bob Woodward that he was a "gut player." How much does your gut actually know?
Plenty. In fact, your gut is so packed with neurons that in the 1990s one gastroneurologist, Michael Gershon, dubbed it the "second brain." This enteric nervous system looks a lot like the network of cells that exists in your actual brain, and it uses all the same neurotransmitters (including 95 percent of the body's serotonin). It can operate on its own—that's without cranial consultation—to start or stop the flow of digestive enzymes, regulate pH levels inside the gut, or expel that week-old sushi that you ate against the better judgment of brain No. 1.
Scientists first caught on to the gut's unique ability to do its own thing around the turn of the last century. Two British scientists, William Bayliss and Ernest Starling, realized that the muscles of a dog's intestine contract in response to pressure. This reflex continued even after the scientists had severed the nerves connecting the intestine to the brain and spinal cord. Other organs (as well as arms and legs) depend upon the central nervous system for this type of behavior. The gut, it seemed, had a mind of its own.
Although the gut is the only organ able to keep itself pumping, churning, and spewing, its "thinking" capabilities are limited. We know when it's telling us it's full or needs to be emptied. But most of the messages that the gut sends never enter our awareness. Within the relatively new field of gastroneurology, scientists are still trying to decode what those messages are and how they affect us at a subconscious level. Some suspect that our emotions could be influenced by these signals from gut to brain.
What about the sensation of knots in your stomach—isn't that the gut's way of telling you to be wary of something (like a terrorist attack)? No, it's the other way around. If your brain perceives that you might be in mortal danger, it tells your body to start shutting down. Digestion would be a waste of much-needed energy in a life-or-death situation, so the lower portion of the gastrointestinal tract contracts to push everything out.
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Explainer thanks Michael Camilleri of the Mayo Clinic, Michael D. Gershon of Columbia University, and Emeran Maye of UCLA.