The cortical projections of the inferior pulvinar and adjacent lateral pulvinar in the rhesus monkey (Macaca mulatta): an autoradiographic study.

An autoradiographic technique was used to determine superior colliculus (SC) and pulvinar projections in the rhesus monkey. SC projects bilaterally to the inferior pulvinar (PI) while occipital cortex projects to PI and the lateral pulvinar (PL). PI has sustaining, topographical projections to layers IV, III and I of areas 18 and 19 (and VI and I of 17) which agrees with the central representation of the visual hemifield and suggests that there is more than one hemifield representation in prestriate cortex. PL adjacent to PI also projects to the same cortical areas and layers, while the portion of PL extending into the caudal pole of the pulvinar projects to layers IV, III and I of areas 20 and 21. Thus, occipital cortices are associated by cortico-thalamocortical connections and also receive direct lemniscal input via SC-PI and the dorsal lateral geniculate nucleus (DLG), while inferotemporal areas 20 and 21 receive only cortico-thalamocortical connections. It is concluded that Stoffels' principle of lamellation holds and, that one pulvinar subdivision projects to several cortical areas, that adjacent pulvinar subdivisions have overlapping projections to these cortical areas and their layers and that the pulvinar also projects to the same cortical area as DLG but to different layers. These connections are similar to those in lower mammals but not to those in the squirrel monkey and bushbaby.