Your Second Brain
Kevin Olden, MD, a professor of medicine and psychiatry at the University of South Alabama School of Medicine in Mobile, has studied the mind/body aspects of digestive diseases for nearly two decades, focusing on the relationship between gut function and stress. MORE asked him to tell us what he’s learned about the so-called "brain in the gut."
Q. Let me get this straight: There’s a brain in my stomach?
A. "People are surprised when they learn about the belly brain, but everyday expressions such as "go with your gut" or being "sick to your stomach" reflect an awareness that the gut has its own emotions and views.
"I suspect so-called gut intuition is most finely developed in people who say the GI system is the first place they experience stress. While the gut may be their weakness, it may also give such people an advantage by providing an early warning about the things they need to change in their lives. Gut feelings are a very definite form of information."
Q. What exactly is this belly brain?
A. "Its technical name is the enteric nervous system, but it is often referred to as the ‘little brain.’ Only it’s not so little: This dense connection of nerves runs the entire length of the digestive system, from your esophagus and stomach to the small and large intestine. It’s estimated that the enteric system contains over 100 million neurons. That’s more than make up the spinal cord."
Q. Why do we need a second brain?
A. "A brain in the gut is critical, or it would not have survived all these years of evolution. The gut is one of the most ancient, primitive parts of the body. Even worms have guts. While it’s a very basic organ, digestion — even in simple organisms — is complicated.
"Evidently, a brain in the gut was required to oversee the process, because it evolved early on. The enteric nervous system can mostly function alone, without instructions from the brain. For all we know, the need to regulate the absorption of nutrients may even precede thinking. And just as the big brain became more complex over time, so too did the little brain.
"The big and little brains maintain intimate communication thanks to nerve pathways that run from the GI tract to the head. The two brains also share many of the same neurotransmitters and chemical-receptor sites, which may explain why their responses frequently seem to parallel each other. Shared receptors may also explain why drugs that act on the brain are prone to triggering side effects in the stomach. Some opiate painkillers and antidepressants in the tricyclic family, for example, can cause constipation."
Listening to Your Stomach
Q. In the past, stomach troubles were often dismissed as psychosomatic. Is this changing with greater knowledge of the role of the enteric nervous system?
A. "It is. Two very common gastric disturbances that fit this category are chronic indigestion, or what doctors call dyspepsia [a feeling of nausea or discomfort in the upper stomach recurring for at least three months] and irritable bowel syndrome [IBS], which is characterized by chronic cramping, bloating, diarrhea, or constipation. These are not trivial complaints. Jointly, these conditions account for more than half the workload of gastroenterologists: About one-quarter of the population is affected by chronic indigestion, and IBS is believed to affect another 20 percent.
"The fact that it’s hard to trace these disorders to any physical cause and that they are often hard to treat has led to speculation that stress or some other psychological problem may contribute to them. That’s particularly true of IBS, which predominantly affects midlife women and often goes hand in hand with anxiety, depression, or trauma — studies have suggested a high rate of IBS among women who had been sexually abused.
"But there’s a danger in assuming that this kind of gastric disorder is all in the head. It could be that we just haven’t figured out the physical abnormality to blame. For example, very new research suggests IBS may be caused by altered activity of the neurotransmitter serotonin in the gut.