Kinematic analysis of upper limb trajectories in Parkinson's disease.

The purpose of this study was to analyze the kinematic properties of upper limb trajectories in Parkinson's disease (PD) patients and to investigate the role of visual feedback from the moving limb. Beyond the characteristic bradykinesia, PD patients differed from controls by generating hand trajectories with asymmetrical velocity profiles that lacked smoothness and were composed of a short initial accelerative phase, followed by a prolonged interval composed of alternating decelerative and accelerative phases. In both groups, the reaction times for movements directed away from the body were longer than for movements directed toward the body; this effect was accentuated in PD. In both groups, initial peak accelerations were significantly larger for distally as compared to proximally directed movements. In the absence of visual feedback from the limb a deterioration in the accuracy of reaching the target was observed in both control and PD patients only for distally directed movements. However, this deterioration and the effect of target location on final accuracy was substantially larger in PD. Taken together, our study suggests that in PD visual information is continuously relied upon for ongoing movement correction, therefore accentuating the bradykinesia. The deficit in final accuracy in the absence of visual feedback reflects the important role played by the basal ganglia in sensorimotor integration.