Examining ventral and dorsal prefrontal function in bipolar disorder: a functional magnetic resonance imaging study

Several lines of research suggest both dorsal and ventral prefrontal cortical dysfunction in bipolar disorder (BD). We used functional magnetic resonance imaging to compare patterns of brain activation in remitted BD patients and controls whilst performing tasks selected for their relative specificity in engaging either the dorsal (n-back sequential-letter working memory task) or ventral (gambling task) PFC. Seven BD patients were selected from participants of the Maudsley Bipolar Disorder Project on the basis of clinical remission, absence of cognitive deficits, and monotherapy with mood stabilisers. Subjects were individually matched by gender, age, and IQ to an equal number of healthy controls. In the n-back task, group differences were only present in response to increasing memory load. Patients did not show the predicted dynamic response in the dorsal PFC, but had increased activation in the parietal cortices. During the gambling task, controls showed significant activation in the ventral and dorsal PFC; this was attenuated in BD patients where increased activation was seen in lateral temporal and polar regions. Our findings suggest that there are trait abnormalities in dorsal and ventral PFC function in BD that may be more pronounced during tasks that rely on ventral-dorsal PFC interaction.