Bimanual movement coordination in spastic hemiparesis.

A Fitts' task was used to examine whether the large movement asymmetry in subjects with spastic hemiparesis can be reduced or eliminated when both limbs are required to perform functionally equivalent tasks. Furthermore, it was determined whether any such benefit was expressed as mutual accommodation, or whether one hand "slaves" the other. Finally, the effect of increased task constraints on the magnitude of the asymmetry was considered. A group of ten students served as controls. Subjects had to grasp small balls and subsequently place them into holes. As expected, large total response time differences were present between the hands of the hemiparetic subjects in the unimanual conditions. However, 92% of the difference between hands was eliminated in the bimanual conditions. It is argued that the observed temporal invariance, or time locking, between hands in the bimanual conditions might be facilitated through the activity of bilateral controls exerted from each hemisphere and neural crosstalk at different levels of the central nervous system. Still, an asymmetric tendency remained in the bimanual conditions: a tendency existed for the impaired hand to reach the "target" later in time compared with the dominant hand. This tendency was enlarged as the asymmetry in task demands for the two limbs increased.