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A fMRI study of a cognitive interference task in patients with bulimia nervosa

The long-term objective of our research is to use functional MR brain imaging (fMRI) to understand better the neural circuitry involved in impulsive behaviors. The proposed study will be part of our ongoing effort to characterize the similarities and differences of many neuropsychiatric conditions in which impulsivity is a critical part of the pathology. The disorders we are studying include Tourette's syndrome, Obsessive-Compulsive Disorder (OCD), and Attention Deficit Hyperactivity Disorder (ADHD). We now propose to study patients with a history of Bulimia Nervosa (BN) using the same experiments we have used in the study of ADHD, OCD and TS patients. BN patients are also plagued by impulsive actions as manifested not only by their binging and purging, but also by the high incidence of drug abuse, shoplifting and suicide in their population [Baum A. 1995],[Fahy 1993]. Furthermore, neuropsychological studies have suggested that the cognitive process of BN patients is impulsive [Kaye, 1995]. Through understanding dysfunction in the circuitry that controls behavioral inhibition we will be better able to design and assess the efficacy of new therapeutics for the impulsivity associated with many disorders. We aim to image the neural systems involved in behavioral inhibition in normal subjects and subjects who have a history of BN. We propose to image the patients as they perform the Simon Spatial Compatibility Task in order to isolate the brain activity specifically associated with impulse control. In this task we present leftwardor rightward-pointing arrows on either side of midline. Subjects are instructed to press a button with either their first or second finger of their right hand to indicate whether the arrow is on the right or left side of the screen. Most (on average 95%) are congruent stimuli (e.g. a right-pointing arrow is shown on the right side of the screen), but incongruent stimuli (e.g. a right-pointing arrow is shown on the left side of the screen) are randomly interspersed among them. Responses to the incongruent stimuli are markedly slow relative to responses to congruent stimuli [Simon, 1967] [Simon, 1969] [Craft, 1970]. The stimulus duration and number are identical to those used in the Stroop, a well-documented interference task. We have previously used this task to show that there are specific fMRl changes associated with the task of responding to incongruent stimuli. An in-press manuscript from our laboratory suggests that the brain regions that are engaged in resolving the interference effects of the incongruent stimuli are similar to those engaged by the Stroop [Peterson, Kane (in press)]. The Simon therefore appears to be a spatial analogue of the Stroop. We prefer to use this task as it will avoid the possible confound posed by reading or language difficulties in patients or subjects. Our specific aims are: 1) To use fMRI to study the neural activity of 20 bulimic teenagers and adults during the Simon task. 2) To compare the brain activity associated with this task in the BN patients with that of 20 age-matched controls performing the same task. 3) To show that task-related changes in fMRl signal can predict important behavioral measures in our models of impulse control.