Transcallosal modulation of a focus of maximal activity in the motor cortex

Evoked potentials were recorded from 170 symmetrical points of the motor cortex in acute experiments on 10 cats anesthetized with chloralose and pentobarbital. Callosal influences on the focus of maximal activity (FMA) were studied during bilateral and unilateral electrical stimulation of the sciatic nerves at different strengths. During weak stimulation division of the corpus callosum was shown to broaden the FMA, but during strong stimulation the FMA was narrowed. It is suggested that transcallosal modulation in the intact brain leads to clearer demarcation of the FMA in the motor cortex and also increases the differences between FMAs arising during stimulation at different strengths.