The enteric nervous system uses more than 30 neurotransmitters, just like the brain, and in fact 95 percent of the body's serotonin is found in the bowels. Given the two brains' commonalities, other depression treatments that target the mind can unintentionally impact the gut.
For example, electrical stimulation of the vagus nerve-a useful treatment for depression-may mimic these signals, Gershon says. Although gastrointestinal (GI) turmoil can sour one's moods, everyday emotional well-being may rely on messages from the brain below to the brain above.
Butterflies in the stomach-signaling in the gut as part of our physiological stress response, Gershon says-is but one example. "A big part of our emotions are probably influenced by the nerves in our gut," Mayer says. The second brain informs our state of mind in other more obscure ways, as well. "Some of that info is decidedly unpleasant," Gershon says. For example, scientists were shocked to learn that about 90 percent of the fibers in the primary visceral nerve, the vagus, carry information from the gut to the brain and not the other way around. "The system is way too complicated to have evolved only to make sure things move out of your colon," says Emeran Mayer, professor of physiology, psychiatry and biobehavioral sciences at the David Geffen School of Medicine at the University of California, Los Angeles (U.C.L.A.). He and other researchers explain, however, that the second brain's complexity likely cannot be interpreted through this process alone. "The brain in the head doesn't need to get its hands dirty with the messy business of digestion, which is delegated to the brain in the gut," Gershon says. We likely evolved this intricate web of nerves to perform digestion and excretion "on site," rather than remotely from our brains through the middleman of the spinal cord. Thus equipped with its own reflexes and senses, the second brain can control gut behavior independently of the brain, Gershon says. Breaking down food, absorbing nutrients, and expelling of waste requires chemical processing, mechanical mixing and rhythmic muscle contractions that move everything on down the line. Much of this neural firepower comes to bear in the elaborate daily grind of digestion. This multitude of neurons in the enteric nervous system enables us to "feel" the inner world of our gut and its contents. The second brain contains some 100 million neurons, more than in either the spinal cord or the peripheral nervous system, Gershon says. Technically known as the enteric nervous system, the second brain consists of sheaths of neurons embedded in the walls of the long tube of our gut, or alimentary canal, which measures about nine meters end to end from the esophagus to the anus. "The second brain doesn't help with the great thought processes…religion, philosophy and poetry is left to the brain in the head," says Michael Gershon, chairman of the Department of Anatomy and Cell Biology at New York–Presbyterian Hospital/Columbia University Medical Center, an expert in the nascent field of neurogastroenterology and author of the 1998 book The Second Brain (HarperCollins).
The little brain in our innards, in connection with the big one in our skulls, partly determines our mental state and plays key roles in certain diseases throughout the body.Īlthough its influence is far-reaching, the second brain is not the seat of any conscious thoughts or decision-making. Underlying this sensation is an often-overlooked network of neurons lining our guts that is so extensive some scientists have nicknamed it our "second brain".Ī deeper understanding of this mass of neural tissue, filled with important neurotransmitters, is revealing that it does much more than merely handle digestion or inflict the occasional nervous pang. As Olympians go for the gold in Vancouver, even the steeliest are likely to experience that familiar feeling of "butterflies" in the stomach.