19 November 2013

MRI points to Brain Activity in Certain Regions of the Brain linked to Level of Willpower for weightloss


ATLANTA -- Patients who lost more weight after gastric bypass surgery had greater activity in executive control regions of their brains when attempting to resist food cravings than those who shed fewer pounds, researchers reported here.
In a functional MRI study, more successful bariatric surgery patients had significantly greater activation of the dorsolateral prefrontal cortex when they were told to fight food cravings while looking at food pictures than those who were less successful, Rachel Goldman, PhD, of Bellevue Hospital at New York University in New York City, reported online in Obesity and at Obesity Week.
This region of the brain is associated with self-control in food-related decision making, and its stimulation can inhibit food craving, Goldman said.
"The difference between patients who are more successful is their ability to utilize executive control circuitry when told to resist food cravings," she reported during an oral presentation.
Although the overall success rates of the various bariatric surgery procedures are high, about 20% of patients don't lose the expected amount of weight or they eventually regain it.
The reasons for these effects are unclear, and little is known about how the brain influences obesity or how it changes after surgery. Obese patients may have heightened arousal to food cues, and previous work has shown that there are differences in neuronal responses to these food cues between overweight and normal-weight patients.
To look at changes in the brain after gastric bypass surgery, Goldman and colleagues studied 31 patients who'd had gastric bypass surgery in the previous 1 to 5 years. The majority were white (87%) and female (84%).
Patients' mean body mass index (BMI) before surgery was 51 kg/m2, and their mean current BMI was 32 kg/m2.
Goldman and colleagues stratified the patients based on how successful they were at weight loss: 24 patients were more successful, with a mean loss of 74% of their body weight, while the other seven patients were less successful, shedding a mean of 39% of their baseline body weight.
The researchers then performed brain scans to assess which areas were responsive to food cues, using the food craving/resisting task. Patients were shown two similar images, one with food and one without. The food image, for instance, would be a scoop of ice cream drizzled with chocolate and a cherry, while the corresponding image would be a snow man with a black scarf and a carrot nose -- all similar in color, texture, and pattern.
Patients were told at different points to either allow themselves to crave the food, or to resist any cravings using whatever strategies they could.
Goldberg said resisting cravings could involve a number of cognitive strategies: "Most of them used self-talk cognitive training, telling themselves to think of something else," she said. "A lot of people, after surgery, now see our pile of bacon image as a pile of fat. So they use a lot of imagery and visualization."
Also, patients weren't allowed to eat for at least 4 hours before their visit, to put them at an appropriate hunger level.
Indeed, different areas of the brain were activated when patients were told to resist rather than crave food. When they craved, there was more activity in the superior parietal, precuneus, and the temporal cortex. When they resisted, there was more activation in the precuneus, posterior insula, and the occipital lobe.
When looking at differences between the more and less successful gastric bypass patients, Goldberg and colleagues found significantly greater activation of the dorsolateral prefrontal cortex in the successful patients than in the less successful patients when they were told to resist their cravings.
Goldberg said the findings could eventually help identify patients who might need more cognitive training before surgery in order to achieve the best results, or it could lead to the development of new therapeutic interventions to improve the success rate of bariatric surgery, although she warned that the results are early and require further study.
The study was supported by Covidien through a grant from the Obesity Society.
Goldman reported no conflicts of interest. A co-author reported research support from the National Institute of Arthritis and Musculoskeletal and Skin Disease and National Institute on Drug Abuse at NIH, the North American Spine Society, and the American Society for Gastrointestinal Endoscopy. Other co-authors reported support from NIH, NovoNordisk, Orexigen Therapeutics, Weight Watchers, Pharmatecture, Vindico CME, Vivus, CMEducation Resources, and CMEIncite.

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