Abstract
The reaction times and kinematics of reach and grasp were analyzed for eight subjects with Parkinson's disease (PD) and eight healthy subjects during three variations of a maximal speed prehension task: (a) grasping a stationary ball as fast as possible, (b) grasping a stationary ball within specific time constraints (520 ms and 450 ms), and (c) grasping a moving ball within the same time constraints. Subjects with PD exhibited bradykinesia when reaching for a stationary ball. When reaching for a moving or stationary ball with temporal constraints, subjects with PD moved as fast as healthy subjects. The reaction times of both groups were shorter when reaching to a moving ball than to a stationary ball, regardless of the time constraint. Subjects with PD had a slower velocity of hand opening and closing, a smaller maximal aperture, and a longer time to maximal aperture than healthy subjects in all task conditions. Thus, visual motion cues and external temporal constraints had a greater effect on reach than on grasp. The results suggest that the bradykinesia observed in individuals with PD during self-determined maximal speed prehension may reflect a strategy used to compensate for deficiencies in the grasp component of the task.
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