Topographical projections of the prestriate cortex to the pulvinar nuclei in the macaque monkey: An autoradiographic study

Abstract

Localized microinjections of tritiated amino acids were made in the prestriate cortex (areas 18 and 19) of macaque monkeys in order to determine the topography of the subcortical projections. It was found that the prestriate cortex projected to the entire inferior pulvinar (PI), lateral pulvinar (PL), dorsolateral nucleus, the lateral posterior nucleus, the reticular nucleus, a portion of the medial pulvinar, superior colliculus, and caudate nucleus but not to the dorsal lateral geniculate nucleus. The projections to the PI were organized according to the topographical representation of the contralateral visual hemifield. The ventral portion of the PL which is immediately adjacent to the PI also received a parallel topographical projection in register with the representation of the visual hemifield and thus is distinguished from the remainder of the PL. The dorsal and caudal portions of the PL (which extend to form the lateral portion of the caudal pole of the pulvinar and are located away from PI) also received projections from prestriate cortex which often appeared as several bands of grains. However, although dorsal prestriate cortex seemed to project to the dorsal portion of caudal PL and ventral prestriate cortex seemed to project to the ventral portion of caudal PL, any further topography in the projections to the dorsal and caudal PL as well as any to the other dorsal group nuclei was difficult to determine. The results point to the conclusion that the PI and the immediately adjacent portion of PL are distinguished from the remainder of the pulvinar by their connectional organization, and each region contains a representation of the visual hemifield. Furthermore, the prestriate projections to these and other regions of the pulvinar form the corticothalamic half of visual and visuomotor cortico-thalamocortical projections which involve all the occipital cortices (areas 17, 18 and 19) as well as inferotemporal, parietal and frontal cortices.