Anatomical substrates for early stages in cortical processing of visual information in the macaque monkey

Abstract

Primate; Parallel pathway; Neuroanatomy; Striate cortex; Prestriate cortex; Visual system 1. Introduction It is known that in many features of its anatomy and physiology, the macaque monkey provides an excellent animal model for the human visual system. Visual psy- chophysical studies of m~Ln and macaque show them to have very similar functional capacities (e.g., [17]). In recent years, researchers' attention has shifted away from primary visual cortex, area V1, to visual pathways extending forward into the temporal and parietal cortices and to their connections with the prefrontal association cortex. Imaging studies suggest that like the monkey, the human cerebral cortex has particular areas special- ized for analysis of different qualities of the visual stimulus (see [107]). A broader knowledge of cortical visual processing suggests that an important factor in determining each area's ,distinctive response properties and overall functional relevance is the channelling of particular types of visual information to that area (for example, direction-selective V1 inputs to area V5; [83]), together with uniquely structured associations between different types of information within each area. This places less onus on each .area being anatomically 'tailor made' for specific tasks, although the degree to which the intrinsic neuropil of different visual cortical areas is uniquely structured still remains to be examined in detail. Channelling of different types of visual information via different routes through the cortical neuropil begins with the distribution of functionally distinct types of thalamic inputs to different laminae in area V1. From the neurons that receive these different inputs, intrinsic V1 pathways lead to different sets of efferent neurons, * Corresponding author. Tel: (+44 1771) 608 6914; Fax: (+44 1771) 608 6850; E-mail: j.levitt@ucl.ac.uk. 0166-4328/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved