Differential effects of cerebellar and basal ganglia pathology on the coordination of bilateral arm movements

• We compared coordination deficits between Parkinson's disease (PD) and cerebellar dysfunction (CD) patients during in- and anti-phase bilateral movements. • Advanced PD patients demonstrated significantly larger relative phase deviations than the controls, but only at the higher frequency (1.55 Hz) and only in the anti-phase mode. • CD patients tended to overshoot the target, while the de novo and advanced PD patients tended to undershoot the target. • The coordination of bilateral movements is affected differently by cerebellar and basal ganglia pathology. The objective of this study was to compare coordination deficits between Parkinson's disease (PD) and cerebellar dysfunction (CD) patients during in- and anti-phase bilateral movements with their forearms. 48 participants were divided into four groups: recently diagnosed (de novo) PD patients; PD patients with an advanced stage of the disease; CD patients; age-matched controls. All participants performed in-phase and anti-phase bilateral coordination movements at two pacing frequencies (1 and 1.55 Hz). For interlimb coordination, relative phasing accuracy was measured; for individual limb movements, oscillation frequency, movement amplitude and harmonicity (smoothness) of each limb movement were examined. Results indicated that advanced PD patients showed larger relative phasing deviations than all other groups, but only at the higher pacing frequency in the anti-phase mode; de novo PD and CD patients were not different from controls. Regarding oscillation frequency, no patient group could move in synchrony with required pacing frequency as well as the controls. Both controls and CD patients tended to overshoot the target, while both PD groups undershot the target. In terms of movement smoothness, CD patients were the worst. These findings suggest that the basal ganglia and the cerebellum pathology may affect bilateral coordination differently: motor deficits observed during bilateral coordination tasks in PD patients may be related more directly to the deficits in interlimb coordination, while those observed in CD patients may be related more to the deficits in inter-joint coordination within each limb, which in turn may affect interlimb coordination during bilateral tasks.