Visual cortical projections and chemoarchitecture of macaque monkey pulvinar

We investigated the patterns of projections from the pulvinar to visual areas V1, V2, V4, and MT, and their relationships to pulvinar subdivisions based on patterns of calbindin (CB) immunostaining and estimates of visual field maps (P1, P2 and P3). Multiple retrograde tracers were placed into V1, V2, V4, and/or MT in 11 adult macaque monkeys. The inferior pulvinar (PI) was subdivided into medial (PIM), posterior (PIP), central medial (PICM), and central lateral (PICL) regions, confirming earlier CB studies. The P1 map includes PICL and the ventromedial portion of the lateral pulvinar (PL), P2 is found in ventrolateral PL, and P3 includes PIP, PIM, and PICM. Projections to areas V1 and V2 were found to be overlapping in P1 and P2, but those from P2 to V2 were denser than those to V1. V2 also received light projections from PICM and, less reliably, from PIM. Neurons projecting to V4 and MT were more abundant than those projecting to V1 and V2. Those projecting to V4 were observed in P1, densely in P2, and also in PICM and PIP of P3. Those projecting to MT were found in P1– P3, with the heaviest projection from P3. Projections from P3 to MT and V4 were mainly interdigitated, with the densest to MT arising from PIM and the densest to V4 arising from PIP and PICM. Because the calbindin‐rich and ‐poor regions of P3 corresponded to differential patterns of cortical connectivity, the results suggest that CB may further delineate functional subdivisions in the pulvinar. J. Comp. Neurol. 419:377–393, 2000. © 2000 Wiley‐Liss, Inc.