The evolution of subcortical pathways to the extrastriate cortex

There are multiple routes for visual information to reach the neocortex from the retina. The most well studied are those that pass through the lateral geniculate nucleus of the thalamus and arrive at cortex primarily within V1. From V1, visual information is then disseminated onto extrastriate cortical visual areas. However, there are other less well-studied pathways that bypass V1 and directly target extrastriate visual fields. These include pathways that route through the K layers of the lateral geniculate nucleus or the pulvinar, either by direct or indirect retinal input via the superior colliculus. The focus of this chapter is on these alternative visual pathways that project to extrastriate cortical areas, our current understanding of their possible evolution by reviewing comparative data across primates and their close relatives, and the insights these pathways could provide in our understanding of visual perception in the normal and injured brain.