A representation of the visual field in the inferior nucleus of the pulvinar in the owl monkey (Aotus Trivirgatus)

Abstract

The study of the comparative anatomy of mammalian brains reveals few developments as striking as the expansion in primates of that region of the thalamus referred to as the pulvinar; yet our knowledge of the functional organization of this region is so limited that the pulvinar has been termed the 'terra incognita of the thalamus'. Portions of the pulvinar have long been suspected of mediating visual functions on the bases of proximity to the known visual centers of the brain stem (the lateral geniculate nucleus and the superior colliculus), early suggestions of direct retinal connections (see ref. 27, pp. 154-155), and deductions from clinical cases. Although ablation experiments have not revealed major visual deficits after pulvinar lesions, portions of the pulvinar are clearly implicated in visual functions by a number of recent anatomical reports. It now appears that part of the pulvinar is extrinsic, as defined by Rose and Woolsey, since it receives a projection from the superior colliculus. In addition, parts of the pulvinar project to occipital and temporal areas of cortex and there is now anatomical, electrophysiological and behavioral evidence which indicates that these occipital and temporal cortical areas are involved in visual functions. Finally, photic evoked responses in the inferior pulvinar of the squirrel monkey and bush baby have been recently reported. In view of the evidence that parts of the pulvinar are visual in function, the object of the present investigation was to determine whether portions of the pulvinar are visuotopically organized. In the present study, electrophysiological mapping has revealed evidence for a topographic representation of the visual field which is coextensive with an architectonic entity, the inferior pulvinar. This result is in close correspondence with a recent report that the striate cortex projects topographically onto the inferior pulvinar in the macaque monkey.

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