Hemiakinesia is a disorder of action in which subjects with a brain lesion exhibit difficulty in moving the contralesional body that cannot be attributed to hemiparesis or peripheral nervous system dysfunction. Subjects with this disorder may fail to gaze to the side opposite a lesion or, when instructed to lift both arms, may fail to elevate the contralesional arm. Crucially, these subjects may be shown in other tasks to have the capacity to perform the task; for example, the subject who fails to lift the contralesional arm when instructed to elevate both arms may succeed in lifting the arm when instructed to lift only that arm.
Evidence for the clinical disorder of hemiakinesia comes from the often-striking effects of hemispace on motor performance. A number of investigators have demonstrated that subjects may perform better when using the impaired limb in the contralesional as opposed to...