Visual topography of V1 in the Cebus monkey

Abstract

The representation of the visual field in the striate cortex (VI) was mapped with multiunit electrodes in the Cebus monkey. Nine Cebus apella, anesthetized with N₂O and immobilized with pancuromium bromide were studied in repeated recording sessions. In each hemisphere, VI contains a continuous representation of the contralateral visual hemifield. The representation of the vertical meridian (VM) forms the external border of V1 except at the anteriormost portion of the calcarine fissure. The representation of the horizontal meridian (HM) divides the area so that the representation of the lower visual field is located dorsally, and that of the upper field ventrally. The convoluted surface of VI can be only partially unfolded, and no precise “flattened” map can be obtained without introducing surface discontinuities. The visual topography of VI is presented in a series of coronal sections and in “flattened” maps. The representation of the central visual field is magnified relative to that of the periphery in VI. The evaluation of the cortical magnification factors measured along isoeccentric and isopolar dimensions in the partially unfolded model of VI revealed anisotropies in the representation of the visual field with larger magnification along isopolar lines than along isoeccentric lines. Receptive field size increases with increasing eccentricity, whereas point image size decreases with increasing eccentricity.