The study is reported in the January issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

According to the study's authors, Rachel Marsh and her colleagues, "[Bulimia Nervosa is a disorder]... primarily affecting girls and women, it is characterized by recurrent episodes of binge eating followed by self-induced vomiting or another compensatory behavior to avoid weight gain. These episodes of binge eating are associated with a severe sense of loss of control."

20 women with bulimia nervosa were compared with 20 females without the disorder on their perfomance on the Simon Spatial Incompatibility task, a task where participants must indicate the direction an arrow is pointing regardless of where it appears on a screen. The task is easier when the arrow direction matches the side of the screen, but more difficult when, for instance, an arrow that points leftward appears on the right side of the screen. Ignoring the side of the screen to focus on the arrow direction requires regulating behavior by fighting the tendency to respond automatically and resolving conflicting messages.

"Patients with bulimia nervosa exhibited greater impulsivity than did control participants, responding faster and making more errors on conflict trials [where the arrow direction and location did not match] that required self-regulatory control to respond correctly," the authors write. "They responded faster on congruent trials following incorrect conflict trials, suggesting impulsive responding even immediately after having committed an error."

Participants underwent functional Magnetic Resonance Imaging while performing the task. This is a brain scanning technology that enables researchers to see which parts of the brain are active. From the fMRI scans it was found that participants with bulimia nervosa were less able to activate "frontal striatal circuits", which is an area of the brain that allows individuals to control voluntary behaviours.

When patients with bulimia did respond correctly on trials in which the arrow side and direction did not match, their frontostriatal circuits did not activate to the same degree as did those of women in the control group.

"We speculate that this inability to engage frontostriatal systems also contributes to their inability to regulate binge-type eating and other impulsive behaviors.", the authors concluded.