Motion opponency in visual cortex

Perceptual studies suggest that visual motion perception is mediated by opp onent mechanisms that correspond to mutually suppressive populations of neu rons sensitive to motions in opposite directions. We tested for a neuronal correlate of motion opponency using functional magnetic resonance imaging ( fMRI) to measure brain activity in human visual cortex. There was strong mo tion opponency in a secondary visual cortical area known as the human MT co mplex (MT+), but there was little evidence of motion opponency in primary v isual cortex. To determine whether the level of opponency in human and monk ey are comparable, a variant of these experiments was performed using multi unit electrophysiological recording in areas MT and MST of the macaque monk ey brain. Although there was substantial variability in the degree of oppon ency between recording sites, the monkey and human data were qualitatively similar on average. These results provide further evidence that: (1) direct ion-selective signals underly human MT+ responses, (2) neuronal signals in human MT+ support visual motion perception, (3) human MT+ is homologous to macaque monkey MT and adjacent motion sensitive brain areas, and (4) that f MRI measurements are correlated with average spiking activity.