Overeaters’ Brains

In order to make it easier to swallow, volunteers were first asked to put small plastic mouthpieces coated with a numbing lidocaine gel in their mouths. The volunteers then rinsed the back of their tongues with more lidocaine. Then the subjects swallowed the balloon, which ended up in their stomachs. The tube was taped to their cheeks. Before asking any volunteers to try the procedure, each of the scientists themselves tried swallowing the balloons and having it filled with water.

Gut to Brain Signals

While the brain activity of volunteers was monitored using functional magnetic imaging (fMRI), the scientists filled the balloons first with about one cup (250 ml) of body-temperature water, and then with about two cups (500 ml). A normal adult stomach can hold about 750 ml. As Wang explains, scientists knew that people respond differently to different volumes of food.

"For that overweight person, the same volume, for them, they might feel, 'Um, not enough.'" Why it's not enough? Because their brain never received the signal. And we knew about it. This is common sense. But there's no scientific proof to show which area of the brain reacts to this."

But Wang's study found the first proof that the initial area of the brain to react to stomach expansion is the amygdala, which is also involved with emotion.

Explains Wang, "The brain, immediately from the amygdala, will send to other areas to decide what a person should do at that point of time."

image: Gene-Jack Wang, Brookhaven National Laboratory

But his results showed that the amygdalas of the overweight people did not respond to the smaller volumes in the balloon.

"The most interesting is that we find that the response to this stomach expansion in the same volume, the lean person responds immediately. But the overweight person, they did not respond," says Wang.

What's more, even at the higher volumes, overweight people showed less activity in this brain area than lean people. Wang says that this stop signal is what helps people balance whether or not to stop eating.

"Turned out in the overweight person, they never receive a signal, so that's why they eat more," adds Wang.

So if overweight people lose weight, will they get this signal, or do they gain weight because they never got the signal? Wang says that is a "chicken and egg" question and scientists still do not know those answers. He hopes further studies will lead to more answers and to treatments for those with eating disorders.

PUBLICATION: NeuroImage, February 15, 2008

AUTHORS: Gene-Jack Wang, Dardo Tomasi, Walter Backus, Ruiliang Wang, Frank Telang, Allan Geliebter, Judith Korner, Angela Bauman, Joanna S. Fowler, Panayotis K. Thanos, and Nora D. Volkow

AUTHORS' INSTITUTIONS: Brookhaven National Laboratory, Mt. Sinai School of Medicine, Department of Anesthesiology of SUNY/Stony Brook, NIAAA/NIDA, St. Luke's/Roosevelt Hospital, and Columbia University, College of Physicians and Surgeons.

RESEARCH FUNDED BY: U.S. Department of Energy, the National Institute on Drug Abuse, the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Alcohol Abuse and Alcoholism and the GCRC at University Hospital Stony Brook