Objective: Motor retardation is a characteristic feature of bipolar depression, and is also a core feature of Parkinson's disease. Within the framework of the functional deafferentiation theory in Parkinson's disease, we hypothesised that motor retardation in bipolar depression is mediated by disrupted subcortical activation, leading to decreased activation of cortical motor areas during finger tapping.
Methods: We used functional magnetic resonance imaging to investigate neural activity during self-paced finger tapping to elucidate whether brain regions that mediate preparation, control and execution of movement are activated differently in subjects with bipolar depression (n = 9) compared to healthy controls (n = 12).
Results: An uncorrected whole-brain analysis revealed significant group differences in dorsolateral and ventromedial prefrontal cortex. Corrected analyses showed non-significant differences in patients compared to controls: decreased and less widespread activation of the left putamen and left pallidum; increased activity in the left thalamus and supplementary motor area; decreased activation in the left lateral pre- and primary motor cortices; absence of activation in the pre-supplementary motor area; activation of the bilateral rostral cingulate motor area.
Conclusion: Both movement preparation and execution may be affected in motor retardation, and the activity in the whole left-side motor circuit is altered during self-initiated motor performance in bipolar depression.