Connections of calbindin-D28k-defined subdivisions in inferior pulvinar with visual areas V2, V4 and MT in macaque monkeys

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 (PI1) 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 PI1. 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 PI1, 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 PI1 nor PIc, suggesting that inferior pulvinar projections do not map the position of visual areas in the cortical mantle.