MRI scans done after bariatric surgery reveal different patterns of brain activation in response to food cues according to a study reported here.

Resistance to craving manifested in activation of multiple regions of the brain in patients who had successful weight loss, whereas unsuccessful weight loss had no consistent activation pattern, Rachel Goldman, PhD, reported at the American Society for Metabolic and Bariatric Surgery meeting.

Successful weight loss was associated with increased activation of the prefrontal cortex, insular cortex, and posterior cingulate during food craving. Unsuccessful weight loss was characterized by activation of the anterior cingulate in response to craving stimulated by pictures of food.

“The major limitation of our study is that we examined participants postoperatively,” Goldman, of New York University in New York City, told MedPage Today. “We did not do brain scans on these patients before surgery. The next big question will be what do the brain images look like before surgery?

“If we’re seeing the same type of activation, then perhaps we can predict who is going to be more successful or if the gastric bypass surgery is changing something in the brain. We really don’t know that for sure, and that would be the next step.”

Clinical experience with bariatric surgery has shown that some patients lose less weight than expected or regain weight after surgery. About 20% of patients have regained much of the weight within 18 to 24 months, said Goldman.

Reasons underlying successful and unsuccessful weight loss are unclear. Even less is known about changes in brain activity that occur as a consequence of obesity.

“Obese individuals may have heightened arousal to food cues,” said Goldman. “Recent functional MRI findings have demonstrated variability in neural responses to food cues when comparing obese and normal-weight individuals.”

To obtain more insight into neuroanatomical characteristics associated with weight-loss outcomes after bariatric surgery, investigators studied 40 patients who had undergone gastric bypass surgery 1 to 5 years in the past.

The study population consisted of 27 patients who attained an appropriate weight-loss trajectory, associated with a median 71.90% excess weight loss, and 13 patients who did not achieve the expected trajectory (median excess weight loss 41.59%).

The study protocol prohibited food intake in the 4 hours prior to brain imaging. Each patient underwent two functional MRI brain scans while viewing 24 photos, consisting of 12 images of food and 12 neutral images, presented in random order.

During one scan, patients were encouraged to give in to cravings elicited by the food images. During the second scan, patients tried to resist the craving urge. Comparing activation patterns of the two groups of patients, investigators developed brain activation maps for each of the two scans.

Results of both scans showed distinguishing patterns of brain activation associated with successful and unsuccessful weight loss after gastric bypass surgery.

Among patients who achieved the expected weight-loss trajectory, resistance to craving was associated with greater activation of the prefrontal cortex, frontal insula, poster cingulate, and pre- and post-central gyri. No unique activation pattern emerged from the scans of patients who had not achieved an appropriate weight-loss trajectory.

“Our study suggests that success after gastric bypass may not just be a function of the gut but is an interaction of the gut and brain craving and control circuits,” said Goldman. “Further studies are warranted to compare brain activation in individuals prior to and after weight-loss surgery in order to determine if there are changes that occur in direct response to surgery.”

Primary source: American Society for Metabolic and Bariatric Surgery
Source reference: Feldman R, et al “Identifying differences in brain activation associated with weight gain and weight loss following gastric bypass surgery” ASMBS 2012; Abstract P-5.

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By Charles Bankhead, Staff Writer, MedPage Today