Cortical mechanisms involved in praxis: observations following partial and complete section of the corpus callosum in man.

In patients who have undergone complete section of the corpus callosum for intractable epilepsy, lateralized presentation of visual nonverbal stimulation showed that the coordination of motor acts by either hand is controlled exclusively by the contralateral hemisphere. When two patients had serial operations consisting of an initial division of the splenium and posterior 3 cm, followed by complete callosal division, an opportunity arose to test the explicit cortical pathways involved in ipsilateral control. Between operations, these patients could not coordinate movements of the hand ipsilateral to the hemisphere receiving the command. This suggested that for visual nonverbal stimulation, the posterior 3 cm of corpus callosum is necessary for control of the ipsilateral hand; the rostral callosum cannot transfer sensorimotor commands. Also, contrary to current views, each hemisphere can carry out sequentially dependent motor activity.