Abstract
Using reaction time experiment (RT), differences of efficiency in simultaneous motions between the left and right side were examined on 10 normal subjects, 10 patients with left hemispheric lesion (LHL) due to cerebrovascular disease, and 10 with right hemispheric lesion (RHL). The subject, responding to sound stimulus presented about 2 sec after a verbal warning, extended his wrist as fast as possible in following conditions: the left or right wrist-extension alone (single condition), and extension of the left or right wrist with dorsiflexion of the ipsilateral ankle (simultaneous condition). EMG activities of finger extensor muscles were picked up with surface electrodes and recorded on a memoscope, where the time elapsed from the stimulus onset to the initial activities (RT) were measured with msec scale. Mean RTs were calculated from 15 trials. Compared to the single condition, RTs of the simultaneous condition were long. RT differences between the two conditions (Δ) were obtained by subtracting RT of the single condition from RT of the simultaneous condition. The right Δ was larger than the left in the normal group, whereas the left Δ was larger than the right in the LHL group. In the RHL group there was no significant difference of Δ between the left and right side. It is assumed that performance of simultaneous motions is more efficient on the left side than on the right in the normal subjects, which would reflect the functional difference between the left and right hemisphere, i. e., serial and parallel processing of information, and asymmetry of channel capacities. However, the result obtained from the patients with LHL and RHL could not be explained by the deficit of such differentiated function, but it should be attributed to functional reorganization after hemispheric lesion.
