Summary:In order to address the hypothesis that striatal lesions can produce hypokinesia of the arm contralateral to the lesion in either hemispace, a patient with an infarction of the right caudate, internal capsule, and part of the globus pallidus was examined. She was administered motor tasks requiring sustained motor activity for her right arm in both hemispaces. She was unable to sustain motor activity in left hemispace, whereas she performed normally in right hemispace. Addition of attentive tasks in the left hemispace decreased motor impersistence in left hemispace, but had no effect on right hemispace. However, addition of attentive tasks in right hemispace increased motor impersistence. The results suggest that the striatum is important for motor function in contralateral space, independent of which limb is performing the task. In addition, unilateral attentive tasks influence this motor function.