Subcortical projections of six visual cortical areas in the owl monkey, Aotus trivirgatus

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Abstract
Subcortical projections of six visual cortical areas (Areas 17 and 18, the Middle Temporal, Dorsomedial and Medial Areas, and the Posterior Parietal Region) in the owl monkey, Aotus trivirgatus, were investigated with autoradiographic methods following injections of tritiated proline. No contralateral projections were demonstrated. While some brainstem structures received input from all six subdivisions of cortex, each cortical area appeared to exhibit its own unique pattern of subcortical projections. All six cortical areas were found to project to the superior and inferior divisions of the pulvinar, reticular nucleus of the thalamus, pretectum and superior colliculus. Other subcortical targets of one or more visual cortical areas were the basal ganglia, claustrum, zona incerta, one or more of the intralaminar nuclei, lateral posterior nucleus, pregeniculate nucleus, dorsal lateral geniculate nucleus, and pontine nuclei. Furthermore, details of corticofugal projections to the dorsal lateral geniculate nucleus, pretectum and superior colliculus varied with the cortical area studied. The projections to the reticular nucleus, pregeniculate nucleus, dorsal lateral geniculate nucleus, the inferior and a portion of the superior division of the pulvinar and the superior colliculus were found to be topographically organized. The targets of the subcortical projections were compared with those of the retina, as revealed by autoradiographic methods following tritiated proline injections of the eye and were found to overlap to varying extents in the superior colliculus, pretectum and dorsal lateral geniculate nucleus and to be segregated in the pregeniculate nucleus. The results substantiate the validity of previous studies in the owl monkey that suggest that the visual cortex is subdivided into several functionally distinct areas and illustrate the complexity of corticofugal influence on visual processing.