Effects of unilateral brain damage on the control of goal-directed hand movements.

Insight into the functional neural substrates associated with the control of goal-directed purposive movements can be obtained through the study of the performance of individuals with brain damage. The control of rapid reciprocal aiming was investigated by comparing ipsilateral limb performance of subjects with unilateral brain damage to that of controls performing with the same limb. Thirty right-hand-dominant individuals, ten with right hemisphere stroke, ten with left hemisphere stroke, 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 techniques. Key kinematic features of the vertical and horizontal components of the trajectories were analyzed using both quantitative and qualitative methods. All subjects with brain damage showed prolonged movement times; however, the locus of the slowing depended on lesion side. Specifically, subjects with left stroke showed deficits in the open-loop component of the movement across all three conditions of task complexity, and a prolonged reversal phase surrounding target impact, particularly in the most complex condition. In contrast, subjects with right stroke showed deficits in the closed-loop phase of the movement prior to target impact, particularly in the most complex condition when visual 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 processing associated with the ballistic component and the timing or triggering of sequential movements. In contrast, the right hemisphere is dominant for processing associated with rapid, on-line visual information even when target location is known and direction is certain.