An investigation of collateral projections of the dorsal lateral geniculate nucleus and other subcortical structures to cortical areas V1 and V4 in the macaque monkey: a double label retrograde tracer study.

Previous anterograde studies in the macaque monkey have shown that, in addition to the projection to striate cortex (V1), the dorsal lateral geniculate nucleus (DLG) has a sparse, horizontally segregated projection to layers IV and V of prestriate cortex (V4). However, the distribution and degree of axon collateralization of DLG cells which give rise to these projections are unknown. This study was designed to answer these questions. The DLG (along with the pulvinar and other subcortical regions) was examined for the presence of single- or double-labeled cells after injections of two different (fluorescent or HRP) retrograde tracers into corresponding retinotopic points in visual cortical areas V1 and V4. In the DLG, it was found that cells projecting to V4, which reside in or near the tectorecipient interlaminar zones of the DLG, do not project to V1 and thus represent a separate population of cells. The organization of the macaque geniculo-prestriate projection thus seems quite different from that of carnivores. Both single- and double-labeled cells were found in other subcortical areas, e.g., single-labeled cells were found in the claustrum, hypothalamus and lateral pulvinar, and a double-labeled cell population was found in the inferior pulvinar.