The Complex Brain in Your Gut
Sandra Blasklee
 New York Times, January, 1996

Ever wonder why people get "butterflies" in the stomach before going on stage? Or why an impending job interview can cause an attack of intestinal cramps? And why antidepressants targeted for the brain cause nausea or abdominal upset in millions of people who take such drugs?

The reason for these common experiences, scientists say, is that the body has two brains - the familiar one encased in the skull and a lesser known but vitally important one found in the human gut.   Like Siamese twins, the two brains are interconnected  -  when one gets upset, the other does, too.

The gut has a mind of its own, the enteric nervous system.  Just like the larger brain in the head, researchers say, this system sends and receives impulses, records and experiences and responds to emotions.  Its nerve cells are bathed and influenced by the same neurotransmitters. The gut can upset the brain just as the brain can upset the gut.

The gut's brain, known as the enteric nervous system, is located in sheaths of tissue lining the esophagus, stomach, small intestine and colon.  Considered a single entity, it is a network of neurons, neurotransmitters and proteins that zap messages between neurons, support cells like those found in the brain proper and a complex circuitry that enables it to act independently, learn, remember and, as the saying goes, produce gut feelings.

The brain in the gut plays a major role in human happiness and misery.  But few people know it exists, said Dr. Michael Gershon, a professor of anatomy and cell biology at Columbia Presbyterian Medical Center in New-York.  For years, people who had ulcers, problems swallowing or chronic abdominal pain were told that their problems were imaginary, emotional, simply all in their heads.  Dr. Gershon said.  They were shuttled to psychiatrists for treatment.

Until relatively recently, people thought that the gut's muscles and sensory nerves were wired directly to the brain and that the brain controlled the gut through two pathways that increased or decreased rates of activity.  Dr. Wingate said.  The gut was simply a tube with simple reflexes.  

Trouble is, no one bothered to count the nerve fibers in the gut. When they did, he said, they were surprised to find that the gut contains 100 million neurons - more that the spinal cord has.  

The gut's brain and the head's brain act the same way when they are deprived of input from the outside world. Dr. Wingate said. During sleep, the head's brain produces 90-minute cycles of slow wave sleep punctuated by periods of rapid eye movement sleep in which dreams occur.  During the night, when it has no food, the gut's brain produces 90-minute cycles of slow wave muscle contractions punctuated by short bursts of rapid muscle movements. Dr. Wingate said.

The two brains may influence each other while in this state.  Dr. Wingate said. Patients with bowel problems have been shown to have abnormal REM sleep. This finding is not inconsistent with the folk wisdom that indigestion can produce nightmare.

Researchers are beginning to understand why people act and feel the way they do.  When the central brain encounters a frightening situation, it releases stress hormones that prepare the body to fight or flee.  The stomach contains many sensory nerves that are stimulated by this chemical surge - hence the "butterflies".  On the battlefield, the higher brain tells the gut brain to shut down.

Similarly, people sometimes "choke" with emotion.  When nerves in the esophagus are highly stimulated, people have trouble swallowing.

Even the so-called "Maalox moment" of advertising fame can be explained by the two brains interacting, said Dr. Jackie D. Wood, chairman of the department of physiology at Ohio State University in Columbus.  Stress signals from the head's brain can alter nerve function between the stomach and esophagus, resulting in heartburn. 

Victims of AIzheimer's and Parkingson's diseases suffer from constipation.  The nerves in their gut are as sick as the nerve cells in their brains.

Just as the central brain affects the gut, the gut brain can talk back to the head. Dr. Gershon said.  Most of the gut sensations that enter conscious awareness are negative things like pain and bloatedness.  Dr. Wingate said. People do not expect to feel anything good from the gut but that does not mean such signals are absent, he said.
 
The human gut has long been seen as a repository of good and bad feelings. Perhaps emotional states from the head's brain are mirrored in the gut's brain, were they are felt by those who pay attention to them.

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