The goal of the present research project is to uncover how the astonishingly complex structure of human and animal brains emerges during development and how it becomes well-suited to perform highly sophisticated behaviors. The PIs will use the latest multi-electrode, imaging and opto-genetic methods of electrophysiology to measure the functional development of neural circuits in the visual cortex from eye opening until the full maturity of the visual system. If successful, this project will reveal how incoming visual stimuli are combined with previous visual memories stored in the brain to interpret the visual environment. This work will illuminate how experience influences the development of the circuitry in the visual cortex. The potential scientific impact of this research is extremely high because it can, through using the visual system as a model example, clarify of how the brain adapts to the environment to perform its function. This work will have a broader impact on the advancement of science, as students and postdoctoral fellows will be trained to integrate the study of behaving animals with advanced neural recording and stimulation technologies. Further, the computer code for performing recordings and analysis will be published on the authors? websites, and the authors will provide instructional tutorials so that others can build upon the methods developed here. The resulting data will be published on the authors? websites so other scientists can examine and extend the results. Finally, insights gained about how the environment influences the development of neural circuitry are likely to have implications that could reach as far as designing more effective educational tools and creating more supportive work environments.