Stomach full? Brain may not know

Overweight people’s brains seem slow to sense satiety

Overweight people’s brains may not know when their stomachs are full, a brain scan study suggests.

The findings come from Gene-Jack Wang, MD, of Brookhaven National Laboratory, Nora D. Volkow, MD, director of the National Institute on Drug Abuse, and colleagues. These researchers have used real-time brain scans to explore addictive behaviours. They’re also looking at interactions between eating behaviours and brain function.

In their new study, Wang and colleagues had 18 adult volunteers swallow balloons -- sections of latex condoms tied off with unwaxed dental floss -- attached to a long tube. Once the balloons were in the patients’ stomachs, the researchers filled them with body-temperature water. The idea was to simulate eating enough food to fill the stomach.

While the balloons were being filled, the researchers scanned the patients’ brains. At various times during the experiment -- when the balloons were partially or fully filled -- the patients were asked how full they felt, how uncomfortable they were, how hungry they were, and how much they wanted food. The patients had not eaten since 7 p.m. the night before the experiments, which were conducted between 11 a.m. and 1 p.m.

Perhaps not surprisingly -- as they had a tube going down their throat -- the patients reported only a little less hunger and a little more desire for food when the balloons were full.

Interestingly, the thinner the subject, the more likely that person was to report feeling full when the balloon was full. The heavier the patients, the less likely they were to feel full with a filled water balloon in their stomachs.

Filling the balloon triggered a response in the amygdala, the part of the brain that controls emotional responses -- and possibly feeding behaviour. Removal of a specific part of the amygdala causes animals to eat uncontrollably.

Interestingly, the left rear amygdala became active when patients reported feeling full.

“This study provides the first evidence of the connection of the left amygdala and feelings of hunger during stomach fullness, demonstrating that activation of this brain region suppresses hunger,” Wang says in a news release.

Wang went on to suggest that possible treatment options for obesity might include brain surgery.

“Our findings indicate a potential direction for treatment strategies -- be they behavioural, medical, or surgical,” he says.

Wang and colleagues report their findings in the Feb. 15 issue of the journal NeuroImage. (Source: www.medicinenet.com)