A neurochemically distinct third channel in the macaque dorsal lateral geniculate nucleus

The primate visual system is often divided into two channels, designated M and P, whose signals are relayed to the cerebral cortex by neurons in the magnocellular and parvicellular layers of the dorsal lateral geniculate nucleus. We have identified a third population of geniculocortical neurons in the dorsal lateral geniculate nucleus of macaques, which is immunoreactive for the alpha subunit of type II calmodulin-dependent protein kinase. This large third population occupies interlaminar regions (intercalated layers) ventral to each principal layer. Retrograde labeling of kinase-immunoreactive cells from the primary visual cortex shows that they provide the geniculocortical input to cytochrome oxidase-rich puffs in layers II and III.