The human neocortex is comprised of many areas that perform high-level functions, ranging from basic sensory processes to cognitive thought. The organization of the neocortex and its connections forms a sophisticated system that generates human thought, perception, action, emotion, and cognition. Abnormalities in this system are the basis for many human developmental psychiatric disorders and syndromes. Most alterations occur developmentally during the time in which the neocortex is divided into discreet, functional areas; however, the mechanism of this regionalization is not well understood. The proposed research will use mice to directly examine the interactions of sensory input and gene expression and their influence on neocortical regionalization, as well as determine how these interactional influences vary by developmental maturity. Understanding the mechanisms involved in brain development will help the larger understanding of the causes of developmental disorders in children.