"Third tier" ventral extrastriate cortex in the New World monkey, Cebus apella

The Ventral extrastriate cortex adjacent to the second visual area was stud ied in the New World monkey Cebus apella, using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstra te the existence of a distinct strip of cortex, 3-4 mm wide, with an ordere d representation of the contralateral upper visual quadrant, up to 60 degre es eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third visual complex (V3v) of Old World m onkeys, also known as the ventral posterior area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, fo rming a congruent border with the fourth visual area (V4). Central visual f ields are represented in posterior and lateral portions of V3v, in the infe rior occipital sulcus, while the periphery of the visual field is represent ed anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ven tral occipitotemporal transition, had neurones that had poor visual respons es. No representation of the lower quadrant was found adjacent to V3v in ve ntral cortex. However, we observed cells with perifoveal receptive fields c entred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue again st the idea that V3v is an area restricted to the ventral cortex in New Wor ld monkeys and support the conclusions of previous anatomical studies in Ce bus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data su ggest that V3v may be part of a larger area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral area described in other New World monkeys.