Human area V5 and motion in the ipsilateral visual field

We have studied area V5 of the human brain with visually-evoked potential ( VEP) and functional magnetic resonance imaging (fMRI) methods, using hemifi eld motion stimuli. Our results confirmed the presence of an ipsilateral fi eld representation in V5 and found: (i) a delay in the ipsilateral response in V5, irrespective of the hemifield stimulated; (ii) a longer ipsilateral delay for left hemifield than for right hemifield stimulation; and (iii) i n a patient with a section of the splenium, an absent ipsilateral response for right but not left hemifield stimulation. Together with neurophysiologi cal and anatomical evidence in the monkey, our non-invasive spatial and tem poral imaging studies in man reveal that ipsilateral V5 is activated by mot ion signals transferred from contralateral V5. The asymmetry of ipsilateral delay in normal subjects and the asymmetrical loss of ipsilateral response following splenial section imply that signals related to visual motion are transferred from one V5 to the other through two segregated pathways.