Limbic Hyperreactivity in Bipolar II Disorder

OBJECTIVE: The authors’ goal was to determine whether patients with bipolar II disorder had altered regional brain responses to novel motor sequences. METHOD: Regional cerebral blood flow was measured with positron emission tomography in 13 patients with bipolar II disorder and 14 healthy comparison subjects. Participants performed a serial reaction time task in which they were visually cued to press one of four buttons at a time. The order of button presses was determined by a complex sequence that was changed in the latter half of the study. RESULTS: In the comparison subjects a spatial attention circuit in the superior parietal lobe and supplementary motor area was activated in response to the introduction of the new sequence. Patients did not display this activation pattern; instead, a widespread limbic network was activated in response to the new sequence. CONCLUSIONS: The attentional resources of patients with bipolar II disorder are not reallocated when they are confronted with a nonemotional motor task; rather, their performance is altered through activation of limbic circuitry.