The effects of brain lesions on the performance of bilateral arm movements.

Abstract An experimental study of the effects of brain lesions on the performance of bilaterally synchronous tapping movements and movements of manipulative skill was undertaken. The subjects were 40 patients with verified left- and right-sided hemisphere lesions and 20 control subjects. The results show that left-sided cortical lesions produce significant impairment in the rapidity of repetitive movements with the ipsilateral as well as with the contralateral arm, whereas right-sided lesions produce impairment of movement in the contralateral arm only. The findings in the test of precise arm movements indicate that there is significant impairment in each arm in the presence of right- as well as of left-sided cortical lesions. Comparison of unilateral with bilateral tapping movements shows that movements performed by normal subjects with the two arms together are significantly slower than the same movements performed by either arm alone. In the patient group there is no significant difference between the rapidity of bilateral arm movements and that of the same movements performed by the left arm alone. The present experiments also indicate that the performance of patients with cortical lesions involving intrahemispheric extensions shows comparatively less reduction in respect of the rapidity of bilateral arm movements than does that of patients without such intrahemispheric involvement. The findings further reveal that bilateral performance of precise movements is significantly slower than the same movements performed by either arm alone, in the control group as well as in the patient group with either left- or right-sided cortical lesions. Some theoretical interpretations of the findings are discussed.