If I understand correctly, the seat of emotion is in the brain, in the limbic system, so why do I get butterflies in my stomach when I’m nervous?

Sincerely,
Stomach Upset

Dear Stomach Upset,

Remember that Steve Martin movie The Man With Two Brains? Well, it turns out they got the number wrong. It should have been The Man With Three Brains. There was the brain Dr. Hfuhruhurr carried around in the jar (voiced by the girl from Wings if I remember correctly), the one in his skull, and the one in his stomach . . . That’s right, his stomach. According to researchers in the field of neurogastroenterology, each of us has not one, but two brains: One that lives on top of our necks, and a second in our guts.

The brain in your stomach is called the enteric nervous system, and it is “located in sheaths of tissue lining the oesophagus, stomach, small intestine and colon.” What identifies this part of your anatomy as a brain, you ask? Like the brain in your melon, the enteric nervous system houses a network of neurons, which send messages back and forth via neurotransmitters, like serotonin and dopamine.

While the enteric nervous system is an independent entity, it generally works in tandem with your brain. When something upsets you mentally, the feeling often manifests in your stomach. How?

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 “butterflies” . . . Fear also causes the vagus nerve [a nerve connecting the abdomen with the brain stem] to “turn up the volume” on serotonin circuits in the gut . . . thus overstimulated, the gut goes into higher gear and diarrhea results.

(Complex and Hidden Brain, Blakeslee, The New York Times)

Scientists believe that the gut’s brain is responsible for more than butterflies and the occasional bout of diarrhea. They think that disorders like irritable bowel syndrome, and chronic abdominal pain may be the result of malfunctions in the enteric nervous system. Researchers in the growing field of neurogastroenterology are currently working to root out the causes of stomach complaints like these.

The question remains: What is the purpose of this second brain? Dr. David Wingate of the University of London believes that that the gut’s brain is a vestige of our evolutionary past. Nervous systems first evolved in tubular animals that attached to rocks and waited for food to float by. As organisms grew more complex, they required a more highly calibrated system for seeking out food and mating partners. This need gave rise to the central nervous system. But the ability to eat and digest was so paramount to the organism’s survival, according to Wingate, that it was too dangerous to stow it the head. Instead, evolution engineered a separate circuit – the enteric nervous system – to control these drives, which was housed in the stomach.

The moral of the story? Falling prey to stress-induced stomach cramps doesn’t mean you have a weak stomach–it means you have a “smart” one.

Got a question for Neurontic? Email orlivan [at] gmail.com.