Movement accuracy constraints in Parkinson's disease patients

This study examined the hypothesis that the kinematics of movements perform ed by PD (Parkinson's disease) patients are differentially affected dependi ng on whether or not the aiming movement has an accuracy constraint. The ai ming movements required elbow extension in the horizontal plane on a digiti zer. There were two movement conditions: (1) one having a spatial accuracy requirement in which the subjects moved to the defined target and stopped o n it; and (2) one requiring the subjects to move toward the defined target without stopping precisely on it. Subjects were instructed to make their mo vements as fast and as accurate as possible in response to the auditory imp erative signal. PD patients modified the movement speed and kinematics depending on the two accuracy conditions. However, when the accuracy constraint was imposed, mo vement slowness observed in the patients was much more pronounced. The most revealing result was localized to the deceleration phase, particularly as the target was approached, The patients also were found to make a higher nu mber of acceleration zero crossings from negative to positive to reach the target, indicating that the movements were more irregular. For the patients , the first acceleration zero crossing from negative to positive occurred m uch earlier in the movement than that for the controls. In addition, when m ovement accuracy was constrained, the number of zero crossings was accentua ted. These data show that when PD patients make aiming movements to a targe t, their deceleration phase becomes longer and more variable. (C) 1999 Else vier Science Ltd. All rights reserved.