Reprinted from Eating Disorders Review
July/August 2011 Volume 22, Number 4
©2011 Gürze Books
Advances in brain-imaging techniques are providing new inroads into the neurophysiology of eating disorders. Functional magnetic resonance imaging, or fMRI, has been very helpful in this realm. fMRI, which is based on measurement of an increase in blood flow to local blood vessels that accompanies neural activity in the brain, does not require injection of contrast media and involves a short scanning time, of from 1.5 to 2 minutes, compared to the 20 to 30 minutes required for a typical positron-emission tomographic study (PET scan).
Identifying eating disorder subtypes by brain activation
Earlier this year, James Lock, MD, PhD and a team at Stanford University School of Medicine found preliminary evidence that during adolescence, eating disorder subtypes may be identifiable in terms of neural correlates of inhibitory control (Am J Psychiatry 2011; 168:55). As Dr. Lock and colleagues noted, behavior and personality characteristics differ among persons with eating disorders, depending on subtype. For example, patients with binge eating or purging behaviors, such as in the anorexia nervosa(AN) binge-purge subtype and/or with bulimia nervosa, often show impulsive and disinhibited personality characteristics. In contrast, those with the restrictive subtype of AN often show overly controlled behaviors.
In this, the first study to examine brain activation associated with response inhibition in adolescents with eating disorders, Dr. Lock and colleagues compared 13 patients with the binge-purge subtype of AN to 14 patients with AN, restrictive subtype, and 13 healthy controls. They hypothesized that brain activation associated with inhibitory control during a Go-NoGo task would be different in teens with eating disorders compared to healthy controls.
To perform the scans, the group used a magnet housed in the Lucas Imaging Center at Stanford University. Subjects performed a rapid jittered event related Go-NoGo task including a series of letters. The subjects pushed a button in response to all letters except for the occasional appearance of the letter X. fMRI images were collected with a scanner and spiral pulse sequence.
The results of the preliminary study supported the hypothesis that differences in neural function could be identified between AN, restricting type, AN binge-purge subtype, and healthy controls during a task that required inhibitory control. Patients with AN binge-purge subtypes showed increased activation in the right dorsolateral prefrontal cortex, an executive control region of the brain, suggesting inefficient or possibly compensatory activation.
Subtypes could be differentiated
Dr. Lock and colleagues note that their preliminary findings suggest that adolescent subjects with binge-purge behaviors and restricting-type AN likely differ from each other on a neural level and therefore risks and effective interventions may not be the same between these two groups. Because the scans were done in a group of adolescents who were not severely malnourished and who had relatively short durations of eating disorder symptoms, the findings suggest that these neural processes occur prior to or early in the evolution of the eating disorder and may not be the result of chronic disease or state-dependent starvation.
Noting the ongoing debate about potential crossover between AN, restricting subtype AN, binge-purge subtype AN, and bulimia nervosa, the authors feel that their current study provides preliminary evidence that, at least during adolescence, eating disorder subtypes may be distinguishable in terms of neural correlates of inhibitory control.