SCALP DISTRIBUTION COMPONENTS OF BRAIN ACTIVITY EVOKED BY VISUAL-MOTION STIMULI

We analyzed the scalp distribution of electrical brain activity elicit ed by visual motion stimuli in 14 healthy adults. Stimuli were square- wave gratings of high or low contrast moving with a velocity of 4.9 de g/s on a computer monitor. Adaptation to motion was varied by changing the so-called duty cycle of stimulus presentation (i.e., the relation of motion to total presentation time) in order to enhance motion-rela ted activity. Data obtained with motion stimuli were compared with che ckerboard pattern reversal evoked activity. Spatial principal componen ts analysis revealed four latent topographical components that account ed for 92.05% of the variance. Two components showed occipital extreme values surrounded by steep potential gradients while another two comp onents displayed lateralized activity. Analysis of the contribution of these spatial components to the observed potential fields revealed si gnificant differences between activity evoked by pattern reversal and that evoked by motion. The topographical patterns of cortical activati on changed rapidly within 240 ms after motion onset. Our results confi rm the sequential and parallel activation of different neuronal genera tors selectively sensitive to physical stimulus parameters of motion s timuli. The converging evidence of specialized quality-specific stream s of sensory processing stemming from single-unit recordings in monkey s and imaging methods is supplemented by our electrophysiological resu lts reflecting the activation of different brain areas.