To examine the effects of medication (on vs. off) and PD severity (mild-to-moderate vs. advanced) on the performance of visually encoded memory guided reaching movements. 

Visual inputs can be used to encode spatial locations and program movements to memorized locations. Studies suggest that the basal ganglia are involved in this visual-motor integration. Patients with Parkinson’s disease (PD), characterized by basal ganglia dysfunction, manifest deficits in visual-motor integration and impairments in memory guided movements. The effects of anti-Parkinsonian medication and PD severity on impairments in visually encoded memory guided movements remain unclear. Examining the effect of medication and PD severity will clarify the role of dopaminergic circuits in visually encoded memory guided reaching and the sustained effectiveness of medication as PD progresses.

Participants with mild-to-moderate (15m, 3f; mean age ± SD: 65.4±5.7 years; off motor UPDRS ± SD, 35.1±8.9) and advanced PD (11m, 3f; 66.2±4 years; 51±13.1) performed a visually encoded memory guided reaching task while on and off medication (12-hour overnight withdrawal), in a completely darkened room, over two separate days. Participants used visual inputs to encode three sequential targets and reached to the memorized targets as accurately as possible. Dependent outcomes included peak velocity and accuracy. All statistical analyses were performed using SAS Proc Mixed.

Medication significantly improved peak velocity (mean difference, 0.35m/s; p<0.01) and accuracy (0.001m; p=0.04) in the mild-to-moderate PD group. Medication had no effect on peak velocity or accuracy in the advanced PD group.