A Brain in Your Heart

Your Backup Brain
There's a "second brain" in your stomach, and it influences mood, what you eat, all kinds of disease, and decision-making. And you thought it was all in your head.
By Dan Hurley, published on November 01, 2011 - last reviewed on October 31, 2011
There is, you may be happy to know, a guru of intestinal intelligence. And as improbable as it sounds, he just may be able to explain why you get depressed and anxious, dive for the peanut butter when you are stressed, and rely on "gut instincts," among many other matters of the mind. Meeting him turned out to be a gut-wrenching experience—literally. When a security guard at Columbia University's College of Physicians and Surgeons kept me waiting 45 minutes in the lobby while checking and rechecking my credentials, my stomach began churning like a washing machine. By the time the guard let me upstairs, I had one question for the researcher regarded as the father of the new field known as neurogastroenterology: Was the pain in my stomach all in my head?

The answer turned out to be double-sided. You see, it depends on which brain you wish to talk about: the one in your head or the other one, in your gut.



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"The gut can work independently of any control by the brain in your head—it's functioning as a second brain," says Michael Gershon, professor and chair of pathology and cell biology at Columbia. "It's another independent center of integrative neural activity."

After five decades of groundbreaking work leading to discovery of the gut's brain—known technically as the enteric nervous system (ENS)—Gershon reassured me that he, too, still feels the twisting of his own intestines under periods of high stress, especially whenever he calls the National Institutes of Health to find out where he stands on his newest research grant applications. "I become painfully aware of the kind of signals the gut can send to the brain," he confides.

That anguish has paid off. With an astonishing 100 million neurons—more than in the spinal cord but a lot fewer than in the brain—arrayed over an intricately folded surface area more than a hundred times greater than that of your skin, he has found, the ENS can work all on its own, without any input from the brain, to control the movement and absorption of food throughout the intestines. No other organ can call its own tune without the baton of that conductor who stands on the pedestal above the neck.

But the ENS, the newest mind-body connection to be revealed—and sometimes considered a branch of the autonomic nervous system, although Gershon sees it as holding its own—does much more than control itself. It also sends signals north to the brain that directly affect feelings of sadness or stress, even influence memory, learning, and decision-making. It relies on, and in many cases manufactures, more than 30 neurotransmitters, including serotonin, that are identical to those in the brain. What's more, tinkering with the second brain in our gut has lately been shown to be a potent tool for achieving relief from major depression. Even autism, studies suggest, may be wrapped up in the neurobiology of the brain down under.
"The nervous system actually started out in the gut," says Emeran Mayer, director of the UCLA Center for Neuro-visceral Sciences and Women's Health as well as of the UCLA Center for Neurobiology of Stress. "Most of my patients have a very good understanding that there is a close connection between their emotions and their guts. But there are still very few neuroscientists who understand the complexity of this enteric nervous system and its links to the brain."

As he explained in a recent article in the journal Nature, creatures low on the evolutionary totem pole, such as helminths, a class of worms, have a single nervous system that is very much like our own ENS. "The ganglia that form the primitive brains of helminths, and eventually the brains of higher mammals, were derived from the more primitive but homologous enteric nervous circuits. Neural circuitries and transmitter systems that have evolved to assure optimal responses to the challenges presented in our internal environment may have been incorporated into the central nervous system during evolution."

It is only logical that the gut should have a nexus of sensors to gather vital information. After all, like the brain in our head, it is engaged in prolonged contact and interaction with the outside world—in this case, via the food we swallow. And it must accomplish an extraordinary feat of transformation. It is the job of the gut to take in an extensive array of external matter, break it down to its component parts, shuttle it off to various internal organs, and turn it into us.