Psychological tests show that women with bulimia nervosa appear to act more impulsively than women who do not have eating disorders, suggests new research, which also found that bulimic women have abnormalities in parts of the brain that regulate behaviour.
Researchers have found that women with bulimia make more errors on tests that require self-control to respond correctly compared to women without the disease.
As well, brain scans showed that parts of the brain that control voluntary behaviours, known as frontostriatal circuits, were not as active in the bulimic subjects during the tests, even when they made mistakes.
"We speculate that this inability to engage frontostriatal systems also contributes to their inability to regulate binge-type eating and other impulsive behaviors," the study's authors concluded.
The research was conducted by a team from Columbia University. The study appears in the January issue of the Archives of General Psychiatry.
Bulimia nervosa is often diagnosed during adolescence or early adulthood. It primarily affects females, and is characterized by repeated instances of binge eating followed by self-induced vomiting to avoid weight gain.
"These episodes of binge eating are associated with a severe sense of loss of control," according to the authors.
Scientists can study the efficacy of the frontostriatal circuits to control voluntary behaviours with what is known as the Simon Spatial Incompatibility task, whereby subjects have to indicate the direction of an arrow regardless of where it appears on a screen.
What can make this test difficult, the researchers explained, is when the arrow points in one direction but appears on the other side of the screen. Focusing on the arrow's direction, rather than its location, requires subjects to regulate their own behaviour by fighting the urge to respond quickly and sort through the conflicting message.
For their study, Rachel Marsh asked 20 women with bulimia nervosa and 20 healthy women to complete the task while hooked up to a functional magnetic resonance imaging (fMRI) machine.
The bulimia nervosa patients registered their responses more quickly and made more mistakes when the arrow's location and direction did not match, and they continued to register quick answers even after making a mistake.
The brain scans showed that the frontostriatal circuits continued to be less active in those with bulimia nervosa than in healthy women, even after they made mistakes.
"These group differences in performance and patterns of brain activity suggest that individuals with bulimia nervosa do not activate frontostriatal circuits appropriately," the authors concluded, which may contribute to impulsive behaviour.
The researchers will conduct further studies on individuals with healthy weights, adolescents who are at the age when bulimia nervosa is often diagnosed and in patients who have symptoms of varying severity.
