Hemispheric specialization in the co-ordination of arm and trunk movements during pointing in patients with unilateral brain damage.

During pointing movements involving trunk displacement, healthy subjects perform stereotypically, selecting a strategy in which the movement is initiated with either the hand or trunk, and where the trunk continues after the end of the hand movement. In a previous study, such temporal co-ordination was not found in patients with left-hemispheric brain lesions reaching with either their dominant paretic or with their non-dominant non-paretic arm. This co-ordination deficit may be associated in part with the presence of a lesion in the dominant left hemisphere. If so, then no deficit should be observed in patients with stroke-related damage in their non-dominant right hemisphere moving with their ipsilesional arm. To verify this, 21 right-hand dominant adults (7 who had had a stroke in the right hemisphere, 7 who had had a stroke in the left hemisphere and 7 healthy subjects) pointed to two targets located on a table in front of them in the ipsilateral and contralateral workspace. Pointing was done under three movement conditions: while not moving the trunk, while bending the trunk forward and while bending the trunk backwards. The experiment was repeated with the non-paretic arm of patients with stroke and for the right and left arms of healthy subjects. Kinematic data were recorded (Optotrak). Results showed that, compared to healthy subjects, arm-trunk timing was disrupted in patients with stroke for some conditions. As in patients with lesions in the dominant hemisphere, arm-trunk timing in those with lesions in the non-dominant hemisphere was equally more variable than movements in healthy subjects. However, patients with dominant hemisphere lesions used significantly less trunk displacement than those with non-dominant hemisphere lesions to accomplish the task. The deficit in trunk displacement was not due to problems of trunk control or sitting balance since, in control experiments, all subjects were able to move the trunk the required distance, with and without the added weight of the limb. Results support the hypothesis that the temporal co-ordination of trunk and arm recruitment during pointing movements is mediated bilaterally by each hemisphere. However, the difference in the range of trunk displacement between patients with left and right brain lesions suggests that the left (dominant) hemisphere plays a greater role than the right in the control of movements involving complex co-ordination between the arm and trunk.