MOTOR SWITCHING ABILITIES IN PARKINSONS-DISEASE AND OLD-AGE - TEMPORAL ASPECTS

Objectives - To investigate capabilities of arm trajectory modificatio n in patients with Parkinson's disease and elderly subjects using a do uble step target displacement paradigm. Methods - Nine patients with P arkinson's disease and seven age matched control subjects were instruc ted to move a stylus towards visual targets presented on a digitising table. Within each session, in some trials the target location was cha nged before initiation of movement and the subjects were to modify the ir movements towards the new target (switching trials). In other trial s the target location was not changed (control trials). This procedure was repeated for four different target configurations, using intersti mulus time intervals of six different durations. The subjects' hand tr ajectories were recorded and their kinematic characteristics were anal ysed. Results - In switching trials, about 40% of the movements were a imed directly toward the final target location in both groups. When th e trajectories were initially directed toward the first target and the n modified toward the second, the reaction time (RT) to the second sti mulus (RT2) was longer than to the first stimulus (RT1). The RT,IRT, r atio was significantly larger in patients with Parkinson's disease tha n in healthy elderly subjects. Conclusions - Patients with Parkinson's disease and elderly subjects are substantially slower in responding t o a required modification of their movement than in responding to the required movement initiation. Patients with Parkinson's disease have i mpaired capabilities in processing simultaneously the motor responses to two visual stimuli presented in rapid succession.