Interhemispheric connection of motor areas in humans.

We attempted to clarify functional interhemispheric connections of motor cortex (MC) by investigating cortico-cortical evoked potentials from human brains in vivo. Three patients with intractable epilepsy who underwent invasive EEG monitoring with subdural electrodes as presurgical evaluation were studied. Electric pulse stimuli were delivered in a bipolar fashion to two adjacent electrodes on and around MC. Cortico-cortical evoked potentials were recorded by averaging electrocorticograms from the contralateral hemisphere. An initial positive triphasic or an initial negative biphasic wave was recorded when the contralateral MCs were stimulated. When the non-MC electrodes were stimulated, no response was recorded. The latencies ranged from 9.2 to 23.8 ms for the initial positive peak, and 25.4 to 39.4 ms for the initial or the second negative peak. The cortico-cortical evoked potentials responses were maximal around the homonymous electrodes with the stimulated electrodes. Our results directly demonstrate the presence of the functional interhemispheric connections originating in MC. The interhemispheric transit time is indicated. The homotopic distribution of the responses indicates that motor coordination of the bilateral bodies is, at least partially, controlled within MC.