Abstract
The aim of the present study was to gain insight into the control which hemiparetic subjects have over fast, unimanual aiming movements. Twelve cerebral palsied hemiparetic and twelve healthy subjects were asked to hit as quickly as possible stationary and moving targets projected onto a fronto-parallel screen. The task was performed with the non-preferred (spastic/non-dominant) and preferred (non-spastic/dominant) arm. Although the pattern of kinematics of hemiparetic subjects generally corresponded with that reported in earlier reaching and grasping studies, the commonly observed prolonged movement time of the non-preferred arm as compared to the preferred arm was absent. The spatial variability of the lateral hand displacements towards stationary targets was highest in the spastic arm of the hemiparetic subjects indicating diminished motion stability. Even though hemiparetic subjects were expected to be unable to adjust their movements flexibly to the position and the velocity of a moving target, they used in the same way as the healthy subjects did an initial estimate of where moving targets would be hit, i.e., they started aiming towards a position in front of the target. In both subject groups this spatial estimate and the movement time varied as a function of target velocity suggesting that the use of target-velocity information in hitting moving targets is unaffected in spastic hemiparetic subjects. The results are related to possible deficits in the regulation of co-contraction underlying movement stability.
