EFFECT OF EYE-MOVEMENTS ON THE MAGNITUDE OF FUNCTIONAL MAGNETIC-RESONANCE-IMAGING RESPONSES IN EXTRASTRIATE CORTEX DURING VISUAL-MOTION PERCEPTION

We have studied the effects of pursuit eye movements on the functional magnetic resonance imaging (fMRI) responses in extrastriate visual ar eas during visual motion perception. Echoplanar imaging of 10-12 image planes through visual cortex was acquired in nine subjects while they viewed sequences of random-dot motion. Images obtained during stimula tion periods were compared with baseline images, where subjects viewed a blank field. In a subsidiary experiment, responses to moving dots, viewed under conditions of fixation or pursuit, were compared with tho se evoked by static dots. Eye movements were recorded with MR-compatib le electro-oculographic (EOG) electrodes. Our findings show an enhance d level of activation (as indexed by blood-oxygen level-dependent cont rast) during pursuit compared with fixation in two extrastriate areas. The results support earlier findings on a motion-specific area in lat eral occipitotemporal cortex (human V5). They also point to a further site of activation in a region approximately 12 mm dorsal of V5. The f MRI response in V5 during pursuit is significantly enhanced. This incr eased response may represent additional processing demands required fo r the control of eye movements.