Identification and visuotopic organization of areas PO and POd in Cebus monkey

Two visual areas of the anterior bank of the parietooccipital sulcus, areas PO and POd, were identified and their visual field representations were studied in six anesthetized and paralyzed Cebus monkeys. The definition of these areas was based on electrophysiological mapping and myeloarchitecture. PO is located in the ventral aspect of the anterior bank of the parietooccipital sulcus and ventral precuneate gyrus. It borders area V2 posteriorly and ventrally in the depth of the parietooccipital sulcus, area V3d laterally, and another undescribed visual area medially. POd was located dorsal to area PO and ventral to architectonic area PE. The representations of the visual field in areas PO and POd are complex. In each hemisphere, these areas have a virtually complete representation of the contralateral visual hemifield. Different from the previously described visual areas, in PO and POd there is a precise organization of isopolar lines and a complex organization of the isoeccentric ones. In PO, as well as in POd, the representation of the horizontal meridian runs dorsoventrally along the parietooccipital sulcus. The upper visual quadrant is represented medially and the lower visual quadrant laterally. A large and complex representation of the periphery, from 20 degrees to 60 degrees eccentricity is present at the lateral and medial portions of these areas. By contrast, the representation of the central 20 degrees is very small in both PO and POd. The central visual field is represented ventrally in PO and dorsally in area POd. Area POd shows a more stratified myeloarchitectonic pattern than PO and both areas can be distinguished from other surrounding areas by their heavier myelinated pattern.