Differences in brain activation at the sight of food may explain why some patients do better than others after bariatric surgery, new research suggests.
The study, presented at the annual meeting of the American Society for Metabolic and Bariatric Surgery in San Diego, showed that gastric bypass patients who lose 50% or more of their excess weight had unique neural responses to images of food.
The brains of these successful patients showed more activation of the prefrontal cortex on functional magnetic resonance imaging in response to food cues.
"We're seeing an increase in activation in areas that correspond to planning and decision making," Dr Rachel Goldman, who led the study at the New York University School of Medicine and Bellevue Hospital Centre, said.
More activity in the prefrontal cortex
In the study, 40 patients submitted to fMRI scans one to five years after gastric bypass. Twenty-seven were considered successful and had lost an average of 71.9% of their excess weight. The 13 unsuccessful patients had lost 41.6% of their excess weight.
While in the scanner, the patients looked at a random mix of pictures of food and neutral images. They first allowed themselves to crave the food, and then in a separate round they tried to resist the craving.
While craving, the successful patients displayed more activity in the left prefrontal cortex, insular cortex, putamen, anterior cingulate, posterior cingulate and the supramarginal gyrus compared to the other patients.
While resisting their cravings, the successful patients again had more activity in the left prefrontal cortex.
Food more rewarding
The unsuccessful patients, on the other hand, showed more activity in the posterior cingulate and precuneous regions while trying not to crave. Those regions are associated with emotion and anticipation of reward.
Dr Jennifer Lundgren, an associate professor of psychology at the University of Missouri-Kansas City who was not involved in the research, told Reuters Health by email that the new findings "are consistent with other fMRI studies showing increased activation in brain regions associated with cognitive control and inhibition after weight loss by both surgical and non-surgical means."
"Those who lose less weight after surgery may find food more rewarding or have increased emotional response to food cues, compared to those who are more successful with weight loss," Dr Lundgren said.
Mindful meditation can improve weight loss
Both she and Dr Goldman raised the possibility of a future test for patients before surgery to better predict outcomes. That may be one of Dr Goldman's targets for future research.
"If preoperative neural imaging can identify the success of surgery, maybe that would tell us if the individual already has the necessary activation of the brain to be successful," Dr Goldman said. "Or maybe there's something going on after surgery that changes the brain activity - an interaction between the surgery and the brain activation. Another area (for study would be whether) cognitive or brain interventions could change that."
In the meantime she speculates that interventions such as mindful meditation or even transcranial direct current stimulation could someday improve weight loss in gastric bypass patients.
(Rob Goodier, Reuters Health, June 2012)
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