Topographic Organization of Extraoccipital Visual Processing Areas in the Macaque

The macaque visual system has long been used as a model for investigating the processing of incoming visual stimuli results from the coordinated work of a distributed network of areas interacting at many different levels (Felleman and Van Essen, 1991). While much is known about the organization and layout of the occipital visual areas, there are still substantial gaps in our understanding of layout and organization of the higher-level areas. The goal of this study is to describe the whole brain functional anatomy using BOLD-fMRI in macaques performing a series of demanding visuospatial attention tasks. We wish to study the spatial specificity of visual responses in terms of contralateral preference, i.e. stronger responses to contralateral visual stimuli, as well as retinotopic organization both in terms of polar angle and eccentricity. We found that most visuospatial processing areas only respond to contralaterally presented stimuli; ipsilaterally presented stimuli evoked little or no activity in these areas. Additionally, we found that LIP, MT, and possibly PITd contained polar-angle maps of the contralateral hemifield. These same areas, plus FEF and area 46, appear to have separate representations of the fovea and periphery. When compared to previous human fMRI studies, these results indicate that there may be significant differences between macaque visual processing areas and their putative human homologues.