Changes in strategy of aiming tasks in Parkinson's disease.

Fundamental differences in bradykinesia in parkinsonian patients and nonparkinsonian elderly subjects were analysed. Our method was an aiming task in which the coordination of eye and hand movements was measured when the subject attempted to catch up with a visual target. The coordinated eye and hand movements started towards the target almost simultaneously in the normal subjects when the target was in the periphery of the visual area. The initial abnormality in parkinsonian patients was an isolated delay of coordinated hand movement. In the typical bradykinetic patients, the hand movement did not start while the target was still in the peripheral visual area but only when the image of the target was near or on the fovea. The aiming tasks were then performed step by step following visual confirmation. Thus patients with typical bradykinesia showed a failure of ballistic hand movement preprogrammed to the visual target in the peripheral visual area, and the strategy of coordination was changed. In contrast, the disturbance of the ballistic hand movement in the nonparkinsonian elderly subjects had no consistent strategy for coordination of the visually guided eye and hand movements.