Some long-term motor effects of cerebral commissurotomy in man

The long-term effects of cerebral commissurotomy on motor co-ordination and dyspraxia were investigated in 8 patients who had undergone complete or partial commissurotomy 5–10 yr previously. Performance on a series of standardized motor co-ordination and manual dexterity tests was compared with the established norms. Although qualitative performance appeared essentially unimpaired on most tests the scores for speed were consistently below normal and also inferior to those reported for patients with various unilateral brain lesions. In certain bimanual tasks requiring rapid alternating motion and interdependent control severe qualitative and quantitative impairments were present. In addition, marked dysgraphia and mild ideomotor-type dyspraxia on the left side, and moderate dyscopia on the right were present up to 10 yr after surgery in patients with complete commissurotomy. It would appear from the results that interhemispheric communication becomes particularly important for motor output to the extent that the tasks involve complex intermanual coordination or hemispheric specialization with ipsilateral control.