TUESDAY, Jan. 6 (HealthDay News) -- Brain circuitry involved in regulating impulsive behavior seems to be less active in women suffering from the eating disorder known as bulimia nervosa.
The frontostriatal regulatory circuits implicated in this study are mediated by both the neurotransmitter dopamine and the neurotransmitter serotonin.
So far, serotonin has been widely implicated in bulimia, which is often treated with antidepressants known as selective serotonin reuptake inhibitors (SSRIs). However, dopamine has not been studied closely in relation to bulimia nervosa.
"These findings argue for looking more directly into dopamine systems in eating disorders," said study author Rachel Marsh, an assistant professor of clinical psychology in the division of child and adolescent psychiatry at Columbia University in New York City.
"It's definitely preliminary . . . but it's not something to ignore," added Mary Tantillo, director of the Western New York Comprehensive Care Center for Eating Disorders. "We need to study this on adolescents who are closer to the onset of illness [Marsh has already started such a study]."
"This is pretty new stuff... We have a fair degree of understanding of the neurochemistry of eating disorders [but this study looked at] what actually happens in the brain when you engage in certain decision-making tasks or activities," said Daniel le Grange, director of the Eating Disorders Program at The University of Chicago and author of Help Your Teenager Beat an Eating Disorder and Treating Bulimia in Adolescence. "The main interest [of the study] at this time would be to understand how these disorders develop. Does the abnormality occur because someone has bulimia nervosa, or does it contribute to developing it?"
At this point, it's not clear if the brain differences are a cause or an effect of the disorder.
"These were adult women who had had the illness for a median of nine years," Marsh said. "We don't know if [the changes are] the product of having the disorder for nine years, or if something determines development of the disorder."
The study was expected to be published in the January issue of the Archives of General Psychiatry.
Bulimia nervosa, characterized by alternating binging and purging episodes (vomiting and taking laxatives being among the more common behaviors), primarily affects girls and women.
Researchers are just beginning to untangle the neurochemistry of eating disorders.
"Patients with bulimia nervosa are very impulsive, not only in an inability to stop eating everything in front of them, but there is also a high prevalence of shoplifting and drug abuse in this population," Marsh said. Mood disorders are also common in these women, indicating that problems with behavioral self-regulation might be at play.
The researchers compared results from fMRI on 20 women (average age about 26) with bulimia nervosa and 20 age-matched controls.
Participants were shown pictures with arrows pointing either left or right and were asked to identify which way the arrows were pointing. In the simple version of the task, the arrows pointing left were on the left side of the screen and the right-directed arrows on the right side of the screen.
For the more difficult component of the task, the leftward-pointing arrow was positioned on the right side of the screen.
"When individuals are performing correctly, they need to engage self-regulatory control or cognitive control. They need to hold back the automatic response strategy in order to perform correctly," Marsh explained.
Women with bulimia nervosa performed faster on the difficult trials and made more errors and, when they were performing the task, they did not engage the same brain circuitry as the controls.
Participants with the most previous bulimic episodes and the highest rates of preoccupation with shape and weight performed the worst on tasks and engaged the frontostriatal circuits the most.
Healthy controls activated the anterior cingulated cortex region of the brain more when making correct responses and the striatum more when delivering incorrect responses.
The U.S. National Institute of Mental Health has more on eating disorders.
SOURCES: Rachel Marsh, Ph.D., assistant professor, clinical psychology, division of child and adolescent psychiatry, Columbia University, New York City; Daniel le Grange, Ph.D., professor, psychiatry and behavioral neuroscience, and director, Eating Disorders Program, University of Chicago; Mary Tantillo, Ph.D., R.N., associate professor, clinical nursing, University of Rochester School of Nursing, and director, Western New York Comprehensive Care Center for Eating Disorders; January 2009, Archives of General Psychiatry