Hemifield visual motion stimulation: an example of interhemispheric crosstalk.

Coherent motion stimulation of the right or left visual hemifield was performed in nine healthy volunteers in order to investigate interhemispheric visuo-visual interaction by means of functional magnetic resonance imaging. The vertical edge of the motion pattern field was located 8 degrees distant from the fixation point to avoid stimulating the vertical meridian, which is represented retinotopically in both hemispheres. Bilateral activation was significant in the middle occipital gyrus (motion-sensitive middle temporal/middle superior temporal areas; BA 19/37). A negative signal change was found in the primary visual cortex including the lingual and fusiform gyri (BA 18/17) and the occipital white matter containing the optic radiation contralateral to the stimulated hemisphere. These data are most compatible with an interhemispheric transfer of visual motion information, most likely through the corpus callosum. Transcallosal transfer of visual motion information, evident as increases (BA 19/37) and decreases (BA 18/17) of the fMRI signals, may be functionally significant for the processing of motion perception.