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Study Links Amygdala to Overeating
> 1/15/2008 1:55:54 PM

Researchers continue to study the elements, both environmental and biological, underpinning the increasing number of overweight or obese individuals in today's society, and the results of a recent study point to the brain as one potential factor involved. The study, which will appear in the February issue of the journal NeuroImage, used brain imagining technology to compare the brains of overweight subjects to those of subjects with normal weights. In doing so, they identified one region of the brain that may affect an individual's likelihood of overeating.

A full stomach prompts signals to the brain which cause feelings of fullness and satisfaction, and the researchers used expandable balloons to simulate these sensations. The study's 18 subjects, who had body mass indices (BMI) between 20 (normal weight) and 29 (very overweight), swallowed balloons, which were then filled with water. The subjects had not eaten since the night before the experiment was conducted, and they were asked about their level of hunger and perception of fullness throughout the experiment. When the balloons were 70% full of water, participants with lower BMIs were more likely than those with higher BMIs to report feeling full.

Using fMRI, the researchers identified one region of the brain, the left posterior amygdala, that seemed to be involved in the participants' perceptions of fullness. This region was more active in subjects who had lower BMIs, and greater activity levels were observed after the participants reported feeling full. Activity in this region of the brain was weakest for participants who reported feeling hungry despite the full balloon in their stomach. The researchers also investigate the role of hormones in the perception of fullness, focusing particularly on ghrelin, a hormone that creates short-term satiety. They found that subjects who experienced the greatest increase in ghrelin after their stomachs were moderately full also experienced the greatest amount of activity in the left posterior amygdala.

The more research into the potential reasons behind the growing problem of obesity, the better we will understand why some people overeat while others stop. This study has shown that when an individual does not feel full after eating a large meal, certain brain circuits may be involved. Hopefully, as researchers examine the factors that contribute to obesity, we will develop new treatment options for those who overeat.

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