The largest imaging study devoted to bulimia identifies differences in several brain areas.
Bulimia is an eating disorder marked by repeated episodes of binge eating. During these episodes, a large amount of food is consumed with a feeling of loss of control. They are followed by behaviors intended to compensate, such as self-induced vomiting. The brain mechanisms associated with the disorder remain poorly understood.
To obtain a more robust picture, the researchers pooled data from 786 participants from 17 international groups. Of these, 369 had bulimia and 417 formed the comparison group. All had undergone an MRI, an examination that makes it possible to observe the structure of the brain without surgery.
The researchers compared the size of different regions and the surface area of the cortex, the brain’s outer layer. In participants with bulimia, the nucleus accumbens had a slightly smaller average volume. This small region is involved in reward and motivation mechanisms, among other functions.
Two areas of the cortex located near the temples also had a smaller average surface area. By contrast, the researchers found no significant difference in cortical thickness. The differences observed are modest: they describe average differences between groups, not an abnormality that could identify a person with the disorder on an MRI.
Another result concerned the frequency of binge-eating episodes. The more frequent these episodes were, the more often reduced surface area was observed in several additional regions. Some are involved in behavioral control, the perception of sensations coming from the body, or the processing of reward.
However, the total number of compensatory behaviors was not associated with any measured anatomical characteristic. This distinction is interesting because binge-eating episodes and compensatory behaviors both contribute to the clinical assessment of bulimia. They therefore do not seem to have the same relationship with brain structure.
The study cannot determine what comes first. The differences observed could promote certain symptoms, result from the disorder, or depend on other factors. The authors nevertheless checked several elements that could have distorted the comparison, including illness duration, depressive symptoms, and the use of psychotropic medications.
Future research will need to follow patients over time. This could determine whether these characteristics change with binge-eating episodes, the disorder, or treatment. Such follow-up would mainly help distinguish a feature present before bulimia from a change that appeared after it developed.