Effects of unilateral brain damage on grip selection, coordination, and kinematics of ipsilesional prehension.

To determine whether the left and right hemispheres play specific roles in goal-directed movements, prehension with the ipsilesional hand was tested in patients with unilateral brain damage. The task required that subjects rotate the hand while reaching for a bar that was presented in different orientations in the frontal plane, thus making high demands on visuospatial processing. The grasped bar had to be put into a hole: under one task condition the placement of the bar was specified, while under another it was not. The constrained task required that the subject anticipate the placing action when planning the initial prehensile movement. Grip selection, reaction times, kinematics of the transport movement, and coordination of hand rotation during transport were assessed in ipsilesional movements of 22 patients with either left or right brain damage (LBD and RBD) and in control subjects. Patients in both groups exhibited performance deficits; however, impairment characteristics differed profoundly between the groups. RBD patients showed prolonged reaction time and degraded kinematics in the unconstrained task, whereas LBD patients performed relatively well when only the orientation of the bar varied, but slowly and frequently incoordinated when the subsequent action was specified. Our findings emphasize the dominant role of the right hemisphere in processing visuospatial aspects of goal-directed movements, whereas the left hemisphere subserves non-spatial aspects of preplanning under increased task demands. Correlations of the patient's performance with results from clinical tests showed that neither deficits in visuospatial perception of RBD patients nor apraxia of LBD patients could account for the observed abnormalities in the use of the ipsilesional hand.