Cortical representation of inward and outward radial motion in man

We have used positron emission tomography to investigate the cortical areas of the normal human brain involved in processing inward (Expansion) and ou tward (Contraction) radial motion simulated with an optic flow stimulus. Th e optical flow display was made out of dots moving radially away from or to ward the center of the display monitor. In the Control condition, the dots' motion was randomized in order to remove any sensation of radial motion. I n the Expansion condition, several loci of activation were observed: visual areas V2-V3 and the superior parietal lobule (BA 7), predominantly in the right hemisphere. In the Contraction condition activation sites were found in the same visual areas (V2 and V3) in the right hemisphere but the increa se in rCBF in these regions was much lower than in the Expansion condition. BA 7 was activated in both hemispheres. When the motion component of the s timulus was isolated by subtracting the static condition from the incoheren t motion condition, we obtained activations of areas V2, V3, and MT (putati ve V5). These results indicate that the detection of radial motion derived from an optic flow stimulus is mediated by structures forming the dorsal pa rt of the visual cortical system and confirm that area MT is not specifical ly involved in flow analysis. (C) 2001 Academic Press.