The Coevolution of the Neocortex and Dorsal Thalamus in Mammals

Abstract Coevolution of the mammalian neocortex and dorsal thalamus occurs within the broader context of diverse mammalian bodies, behavior, lifestyles, and environmental context, the latter of which is composed of unique, complex patterns of sensory stimuli which must be transduced and interpreted by the brain. Natural selection targets behavior and modifies sensory systems to process incoming patterns of input and generate adaptive behavior for a given context. The dorsal thalamus is the primary source of sensory input to the neocortex, and it plays a central role in integrating information from the neocortex to shape motor output. This chapter examines the coevolution of the dorsal thalamus and neocortex in mammals, focusing on studies that have characterized the relative size of primary sensory cortical fields and nuclei of the thalamus that provide their primary inputs. Because most data on scaling of the cortex and thalamus come from work on the visual system, the authors use examples from this system (dorsal lateral geniculate nucleus, pulvinar complex, and primary visual cortex) to demonstrate how species vary in thalamocortical organization more generally. Finally, they consider several theories that propose why thalamocortical relationships vary across lineages.