A preliminary longitudinal fMRI study of frontal-subcortical circuits in bipolar disorder using a paced motor activation paradigm

BackgroundCompelling evidence suggests abnormal functioning of frontal-subcortical (FSC) circuits in bipolar disorder, but it is unknown whether these are state or trait abnormalities. Longitudinal functional neuroimaging studies may help clarify this issue. However, studies to date have not determined which activation paradigms may be most useful for this purpose. A paced motor task has the potential to be more reliable than cognitive or emotional activation paradigms.MethodsTo evaluate the utility of a paced motor activation task as a longitudinal probe of FSC function, we conducted fMRI scans of 10 subjects with bipolar I disorder when euthymic. We compared activation patterns to the same subjects who had been previously scanned during an episode of depression.ResultsThe paced motor task resulted in activation in the bilateral striatum which was consistent across mood states as well as greater activation among the subjects when euthymic in the right anterior cingulate and medial frontal gyrus.LimitationsThe study sample was small (10 subjects) which limits generalizability of findings.ConclusionsTo our knowledge, this is the first longitudinal study of bipolar illness utilizing a paced motor task. These findings suggest that a paced motor task is useful as a longitudinal probe of both state and trait function in bipolar disorder. Further, this study provides preliminary evidence that striatal functional abnormalities may represent a trait characteristic.