By PT Staff, published on May 1, 1999 - last reviewed on January 23, 2015
Ever get a gut feeling about someone, or I anxious butterflies in
your stomach? That's because you have a second brain in your bowel,
according to Michael Gershon, M.D., author of The Second Brain
(HarperCollins, 1999), and a neurobiologist at New York's
Columbia-Presbyterian Medical Center. Gershon recently explained to PT
how an independent network of over 100 billion neurons in the gut not
only signals our bodies to stress but causes illness.
Q Why do we need a second brain?
A Most importantly, to control digestion. It also works with the
immune system to protect us from hostile bacteria.
Q Does it use neurotransmitters?
A Actually, 95% of all serotonin in the body is in the gut, where
it triggers digestion. Nerve cells in the gut also use serotonin to
signal back to the brain. This information can train us not to eat
certain foods by communicating pain, gas and other terrible
Q Does the brain in our heads influence the "second brain"?
A Yes. Butterflies in the stomach arise when the brain sends a
message of anxiety to the gut, which sends messages back to the brain
that it's unhappy. But the gut can also work in isolation.
Q How does this brain influence irritable bowel syndrome (lBS),
which many believe is a psychological problem?
A Irritable bowel syndrome, whose symptoms include abdominal pain
accompanied by loose stool, affects 20% of Americans. But doctors often
dismiss its severity, attributing IBS to psychoneurosis because they
don't know exactly what it is. I propose that the second brain is the
cause. Antidepressants like SSRIs, when used in doses too low to treat
depression, are effective immediately in IBS patients. Prozac takes weeks
to kick in. This suggests that the drugs work not on the brains of people
with IBS, but in the bowel.