AREA V4 IN CEBUS MONKEY - EXTENT AND VISUOTOPIC ORGANIZATION

We used electrophysiological mapping and myeloarchitectural criteria i n order to define the location, extent and visual topography of the fo urth visual area (V4) in anesthetized and paralyzed Cebus monkey. Base d on these criteria, the borders of V4 with surrounding areas were def ined both on the dorsal and ventral cortical surfaces. In addition, to better visualize the visuotopic organization and to evaluate its regu larity, we constructed bidimensional maps and projected the recording sites onto them. Area V4 has an almost complete representation of the binocular visual field with the lower visual field represented dorsall y (V4d) and the upper field ventrally (V4v). We found this representat ion to he more extensive than those previously described. The represen tation of the central portion of the visual field is largely expanded in comparison with that of the periphery. This emphasis in central vis ion could be related with the involvement of V4 in the ventral stream of visual information processing. Receptive field size increases with increasing eccentricity, while cortical magnification factor decreases . The cortical magnification factor measured along isopolar lines is, on average, 1.5-2.0 times greater than that measured along the isoecce ntric lines, suggesting the existence of a small anisotropy in central and peripheral V4.