Different mechanisms involved in interhemispheric transfer of visuomotor information.

Twenty-one subjects underwent event-related fMRI while carrying out a simple visuomotor task in which they responded to stimuli flashed either onto the right visual field, onto the left visual field, or onto both visual fields at once. The aim of this study was to clarify areas of brain activity associated with crossed-uncrossed differences (CUD) and to investigate differences of the brain activity between CUD and redundancy gain. An intriguing brain activation related to CUD was found in the genu of the corpus callosum (CC). The sites of activation related to redundancy gain were the extrastriate cortex and the cingulate cortex. Our results suggested that CUD depended on the interhemispheric transfer via the CC, and that CUD and redundancy gain involved different brain mechanisms.