Sensory information (such as vision, hearing, and touch) is transmitted through various stations in the brain as it is relayed to the cortex. This proposal tests a novel hypothesis that during development, the cortex sends information to guide the development of these stations. A feed-forward and feedback communication between different regions of the brain could result in the spreading of an initially focal abnormality. This could be the underlying cause of neurodevelopmental diseases such as Rett Syndrome and autism spectrum disorders (ASD). A mouse model of Rett syndrome (RTT) that has impaired development of visual function will be used to understand the developmental relationship between the thalamus and the cortex. A feed forward and feedback interaction between the central nervous system (CNS) structures would mean that defects in one area could affect the other and amplify over time or that changes in one structure can compensate for defects in the other. Thus, a deeper understanding of the developmental relationship between the thalamus and cortex could have implications in neurodevelopment disorders such as ASD.