Binge eaters’ brains flood with dopamine when they see or smell food, according to a new study, priming the brain to see reward similar to the way drug addicts’ brains do.
The brain imaging study at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory revealed a subtle difference between ordinary obese subjects and those who compulsively overeat, or binge.
Dopamine is a well-know brain substance that improves the connection or flow of impulses between nerve cells. Dopamine is also linked to reward and motivation, and may play a role in compulsive overeating.
The findings — published online in the journal Obesity — suggest that this dopamine spike may play a role in triggering compulsive overeating.
Brain scans comparing the effects of methylphenidate plus food stimulation to placebo plus neutral stimulation in obese binge eaters and obese control subjects who were not binge eaters.
Since the radiotracer competes with the brain’s natural dopamine to bind to receptors, a weaker signal from the tracer (less red) indicates more dopamine in the brain.
The decrease in red in the binge eaters exposed to food and methylphenidate compared to the placebo/neutral stimulation condition therefore indicates that food stimulation triggered a spike in dopamine levels in these subjects.
There was no difference in dopamine levels between these conditions in the non-binge eaters.
“These results identify dopamine neurotransmission, which primes the brain to seek reward, as being of relevance to the neurobiology of binge eating disorder,” said study lead author Gene-Jack Wang, M.D.
Previous studies conducted by Wang’s team have identified a similar dopamine spike in drug-addicted individuals when they were shown images of people taking drugs, as well as other neurochemical similarities between drug addiction and obesity, including a role for dopamine in triggering desire for drugs and/or food.
“In earlier studies of normal-weight healthy people who had been food-deprived for 16 hours, we found that dopamine releases were significantly correlated with self-reports of hunger and desire for food.
“These results provided evidence of a conditioned-cue response to food,” Wang said.
In the current study, the researchers suspected that binge-eating obese subjects would show stronger conditioned responses to food stimuli when compared with non-binging obese subjects.
“Understanding the neurobiological mechanisms underlying food stimulation might point us toward new ways to help individuals regulate their abnormal eating behaviors,” Wang said.
The scientists studied 10 obese people with a clinical diagnosis of binge eating disorder, based on evaluations at St. Luke’s-Roosevelt Hospital, and 8 obese subjects who were not binge eaters.
The scientists used positron emission tomography (PET) to scan the subjects’ brains after injecting a radiotracer designed to bind to dopamine receptors in the brain.
Because the tracer competes with the brain’s natural dopamine to bind to these receptors, the signal picked up by the PET scanner provides an inverse measure of the brain’s dopamine levels: a strong signal from the bound tracer indicates low levels of natural brain dopamine; a low signal from the tracer indicates high levels of dopamine in the brain.
“So the key difference we found between binge eaters and non-binge eating obese subjects was a fairly subtle elevation of dopamine levels in the caudate in the binge eaters in response to food stimulation,” Wang said.
“This dopamine response is in a different part of the brain from what we’ve observed in studies of drug addiction, which found dopamine spikes in the brain’s reward center in response to drug-associated cues.
The caudate, in contrast, is believed to be involved in reinforcement of action potentially leading to reward, but not in processing of the reward per se.
“That means this response effectively primes the brain to seek the reward, which is also observed in drug-addicted subjects,” Wang said.
Inasmuch as binge eating is not exclusively found in obese individuals, the scientists believe further studies are warranted to assess the neurobiological factors that may differentiate obese and non-obese binge eaters.
Source: Brookhaven National Laboratory