Regions of brain associated with satiety isolated in study.

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A new imaging study that has identified areas of brain activation associated with feelings of fullness may provide new therapeutic targets to minimizing overeating.

Researchers at the U.S. Department of Energy's Brookhaven National Laboratory found that not only are the left amygdala, left posterior insula, and left precuneus activated during periods of increased stomach volume, subjects with a body mass index (BMI) in the overweight range had less activation of these regions than did those with healthy BMIs under the same conditions (NeuroImage 2007[Epub doi: 10.1016/j.neuroimage. 2007.11.008]).

"By stimulating feelings of fullness with an expandable balloon, we saw the activation of different areas of the brain in normal weight and overweight people," said lead author Dr. Gene-Jack Wang.

To study the brain's response during gradual distention produced by moderate food intake, and to better understand the mechanisms underlying normal and abnormal eating behavior, the researchers used gastric balloon distention. During this procedure, a balloon is placed in the stomach and filled with water warmed to normal body temperature (37[degrees] C). Previous functional MRI (fMRI) studies using this technique have used sudden volume changes, but for this study, balloon volume was changed slowly to study the brain's response to slow stomach distention that mimics normal food intake.

During the cycles, after 30 seconds the empty balloon was filled with 500 mL of water over a 90-second period. When volume reached 500 mL, flow was interrupted for 30 seconds and then the ballon was emptied over a 90-second period. After a 30-second pause, the cycle was repeated.

The study involved three female and 15 male healthy volunteers (mean age 32 years), with a BMI below 30 kg/[m.sup.2] (average 24.4). Participants were studied between 16 and 18 hours after the last meal.

During the last 16 seconds of the pauses, participants rated their fullness, discomfort, hunger, and desire for food. The questions were projected on MRI-compatible goggles. Participants chose one of four possible answers--not at all, just a little, somewhat, and very much--by pressing one of four colored buttons.

Activation of the left amygdala was associated with larger volume conditions (greater than 250 mL). Activation of the right posterior insula was associated with the entire range of volumetric conditions. Activation of the left posterior insula was associated with volume between 250 and 500 mL. Activation of the left precuneus was associated with volumes of 500 or 250 mL and water outflow.

"The main finding of this study was that gastric distention activated [the] left posterior amygdala," the researchers wrote. The amygdala plays a role both in emotional reactions (which is important in the establishment of conditioned responses) and in feeding behavior. The posterior insula is involved in processing somatic and visceral sensations.

The researchers also found that a greater BMI was associated with decreased activation of the right amygdala/hippocampus and insula. Subjects who reported the largest changes in the perception of fullness had the lowest activation of the left posterior amygdala.

BY KERRI WACHTER

Senior Writer