Dynamic changes in cerebello-thalamo-cortical motor circuitry during progression of Parkinson's disease

Both the basal ganglia and cerebellum are known to influence cortical motor and motor-associated areas via the thalamus. Whereas striato-thalamo-cortical (STC) motor circuit dysfunction has been implicated clearly in Parkinson's disease (PD), the role of the cerebello-thalamo-cortical (CTC) motor circuit has not been well defined. Functional magnetic resonance imaging (fMRI) is a convenient tool for studying the role of the CTC in vivo in PD patients, but large inter-individual differences in fMRI activation patterns require very large numbers of subjects in order to interpret data from cross-sectional, case control studies. To understand the role of the CTC during PD progression, we obtained longitudinal fMRI 2 years apart from 5 PD (57±8 yr) and five Controls (57±9 yr) performing either externally- (EG) or internallyguided (IG) sequential finger movements. All PD subjects had unilateral motor symptoms at baseline, but developed bilateral symptoms at follow-up. Within-group analyses were performed by comparing fMRI activation patterns between baseline and follow-up scans. Between-group comparisons were made by contrasting fMRI activation patterns generated by the more-affected and less-affected hands of PD subjects with the mean of the dominant and non-dominant hands of Controls. Compared to baseline, Controls showed changes in CTC circuits, but PD subjects had increased recruitment of both cortical motor-associated and cerebellar areas. Compared to Controls, PD subjects demonstrated augmented recruitment of CTC circuits over time that was statistically significant when the IG task was performed by the hand that transitioned from non-symptomatic to symptomatic. This longitudinal fMRI study demonstrates increased recruitment of the CTC motor circuit concomitant with PD progression, suggesting a role of the CTC circuit in accommodation to, or pathophysiology of, PD.