EFFECTS OF UNILATERAL BRAIN-DAMAGE ON THE CONTROL OF GOAL-DIRECTED HAND MOVEMENTS

Insight into the functional neural substrates associated with the cont rol of goal-directed purposive movements can be obtained through the s tudy of the performance of individuals with brain damage. The control of rapid reciprocal aiming was investigated by comparing ipsilateral l imb performance of subjects with unilateral brain damage to that of co ntrols performing with the same limb. Thirty right-hand-dominant indiv iduals, ten with right hemisphere stroke, ten with left hemisphere str oke, and ten age-matched controls performed unconstrained alternating tapping movements under three conditions of task complexity. The path of the stylus was recorded by video using two-dimensional kinematic te chniques. Key kinematic features of the vertical and horizontal compon ents of the trajectories were analyzed using both quantitative and qua litative methods. All subjects with brain damage showed prolonged move ment times; however, the locus of the slowing depended on lesion side. Specifically, subjects with left stroke showed deficits in the open-l oop component of the movement across all three conditions of task comp lexity, and a prolonged reversal phase surrounding target impact, part icularly in the most complex condition. In contrast, subjects with rig ht stroke showed deficits in the closed-loop phase of the movement pri or to target impact, particularly in the most complex condition when v isual information was necessary for accuracy. Together, these results suggest that for the control of rapid goal-directed aiming movements, the left hemisphere is dominant for task-relevant aspects of processin g associated with the ballistic component and the timing or triggering of sequential movements. In contrast, the right hemisphere is dominan t for processing associated with rapid, on-line visual information eve n when target location is known and direction is certain.