Hemifield visual motion stimulation: An example of interhemispheric crosstalk

Coherent motion stimulation of the right or left visual hemifield was perfo rmed in nine healthy volunteers in order to investigate interhemispheric vi suo-visual interaction by means of functional magnetic resonance imaging. T he vertical edge of the motion pattern field was located 8 degrees distant from the fixation point to avoid stimulating the vertical meridian, which i s represented retinotopically in both hemispheres. Bilateral activation was significant in the middle occipital gyrus (motion-sensitive middle tempora l/middle superior temporal areas; BA 19/37). A negative signal change was f ound in the primary visual cortex including the lingual and fusiform gyri ( BA 18/17) and the occipital white matter containing the optic radiation con tralateral to the stimulated hemisphere. These data are most compatible wit h an interhemispheric transfer of visual motion information, most likely th rough the corpus callosum. Transcallosal transfer of visual motion informat ion, evident as increases (BA 19/37) and decreases (BA 18/17) of the fMRI s ignals, may be functionally significant for the processing of motion percep tion. (C) 2000 Lippincott Williams & Wilkins.