Connections between the pulvinar nucleus and the prestriate cortex in the squirrel monkey as revealed by peroxidase histochemistry and autoradiography

Abstract

Summary Connections between the pulvinar nucleus and the dorsolateral prestriate cortex in the squirrel monkeys were demonstrated by means of retrograde axonal transport of horseradish peroxidase (HRP) and orthograde transport of tritiated leucine ([3H]L) in two sets of animals. The HRP experiments showed that a significant portion of both the inferior (PuI) and lateral (PuL) subdivisions of the pulvinar nucleus project to the dorsolateral prestriate cortex. The labeled cells form laminae or slabs which extend in a rostroventrolateral to caudodorsomedial direction, parallel to the external surface of PuI and PuL respectively. The lateral and medial slabs in both PuI and PuL differ in that large labeled neurons are prominently found within the lateral slabs, whereas the medial slabs are composed mainly of densely packed medium-sized neurons (PuL) or small neurons (PuI). There is continuity between the medial slab in PuL and that in PuI so that functionally these two subdivisions may be more closely related than has previously been recognized. The autoradiographic experiments also revealed a laminar or slab-like pattern of distribution of corticopulvinar projections that span again in a rostroventrolateral to caudodorsomedial direction, thus complementing the laminar distribution of pulvinocortical cells. Each slab is interpreted as a composite of rostrolateral to caudomedially oriented parallel columns of labels following a dorsal to ventral row of injections in the dorsal prestriate cortex. The relationship between the prestriate cortex and PuI-PuL complex is topographical, reciprocal and well-organized. This study points to the importance of PuL, in addition to PuI, as a vital subcortical visual center mediating a thalamoprestriate pathway that is parallel to the primary geniculostriate pathway.