Roles of Thalamocortical Axons in Cerebral Cortical Development

In the adult mammalian brain, thalamocortical input supports key cortical functions by conveying ascending information from subcortical sensory and motor centers and linking different cortical areas. Studies in the 1980s revealed that these afferent projections are also critical for building the mature neocortex, which is composed of six layers and dozens of anatomically and functionally distinct areas. Recent studies have begun to provide a comprehensive view of cortical development, encompassing early regionalization of immature cortical tissue, distinct behaviors of various progenitor cell types, fate specification of neurons forming the six layers, and morphological and functional maturation of each neuronal type leading to the formation of distinct areas. Many of these processes are now known to be influenced by thalamocortical input. This review highlights the historical contexts in which the roles of the thalamus were uncovered, drawing on evidence from a wide range of organisms, cortical regions, and cell types.