To establish the topography of the lateral division of the lateral posterior region (LP1) projections to area 18, up to five different anatomical tracers were injected in separate rostrocaudal locations in area 18 of four adult cats, and patterns of retrogradely labeled LP1 cells were identified. LP1 inputs to area 18 arose from both caudal and rostral nuclei and were topological, organized in patterns that indicate that lower visual space is represented anteroventrally, and more central and upper visual space is represented caudodorsally. In the caudal LP1 nucleus, patches of labeled cells formed bands that ran parallel to the medial and lateral LPI borders and encompassed medial portions of the nucleus. In rostral LP1, the patches of labeled cells formed clusters giving the connections with area 18 a more modular appearance, and were nearer the lateral LP1 border. Injections made nearest area centralis representations in area 18 labeled more neurons than injections in cortex representing more peripheral visual space. Also, neighboring injections in area 18 labeled overlapping patches of cells, but no double-labeled cells were observed. These findings are consistent with previous conclusions based on electrophysiological mapping studies, that two retinotopically organized nuclei constitute LP1.

We examined the relationship between calbindin-D28k-defined subdivisions in the macaque inferior pulvinar and the patterns of afferent connections to cortical visual areas MT, V4 and V2. The subdivisions identified included the posterior (PIp), medial (PIm), central (PIc) and lateral (PIl) subdivisions. Projections to MT and V4 were largely segregated in the inferior pulvinar: projections to MT originated mainly from PIm, while projections to V4 originated mainly from PIl. In addition, weaker projections to MT were observed from PIp and PIc, and some projections from PIp to V4 were observed in one of two cases. Projections to V2 originated preferentially from PIl, with a lesser projection from PIc. No labeled cells were observed in PIm in five monkeys injected with various tracers into different regions of V2. Since most V2 injections were large enough to involve several neighboring stripe-like compartments, these findings suggest that PIm does not project to V2 compartments associated with neither dorsal nor ventral cortical processing streams. Cells projecting to V4 were not strictly segregated from those projecting to V2 in neither PIl nor PIc, suggesting that inferior pulvinar projections do not map the position of visual areas in the cortical mantle.