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

BACKGROUND: Compelling 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. METHODS: To 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. RESULTS: The 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. LIMITATIONS: The study sample was small (10 subjects) which limits generalizability of findings. CONCLUSIONS: To 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.

A functional MRI study of a paced motor activation task to evaluate frontal-subcortical circuit function in bipolar depression.

The primary aim of this functional magnetic resonance imaging (fMRI) study was to test the utility of a paced motor activation task to evaluate frontal-subcortical (FSC) circuit function in bipolar depression. A secondary aim was to determine if utilizing both a motor and cognitive activation paradigm (Stroop) would provide information about the potential role of FSC dysfunction in the cognitive symptoms of bipolar depression. Analysis of the control group (n=15) alone revealed that the motor task activated FSC structures. Comparison of the control to bipolar group (n=14) revealed significant differences between the groups in striatum as well as cortical areas with FSC connections in response to the non-dominant-hand motor task. In response to the Stroop, there were significant differences between the groups in portions of the bilateral posterior cingulate and occipital cortex, but not in FSC structures. While these results must be considered preliminary, this work supports further studies of paced motor tasks to probe FSC function. Further, it suggests that the use of both a cognitive and motor task in the same study provides useful information about brain function. Finally, it supports the literature implicating FSC circuit abnormalities in bipolar disorder.