How the brain's cerebral cortex functions, and how this function goes awry in diseases like autism and mental retardation, remain unknown. Investigators in this study will examine how the rat brain processes and encodes touch information through face whiskers. Specifically, they will study quantitatively how surface texture is transformed into a pattern of vibrations by the sensory periphery (the whiskers, which function similarly to human fingertips), and encoded by action potentials in populations of neurons in part of the brain that processes touch information, the whisker somatosensory cortex (S1). Using gold-standard techniques to measure sensory information and modern optogenetics techniques to activate cortical neurons using light, investigators will identify the physical and neurobiological signals that convey information about surface texture in somatosensory cortex. Such baseline knowledge about normal cerebral cortex function is critically needed to understand cortical processing defects in autism, mental retardation, and other neurological diseases. Because rodent S1 is a major disease model for Fragile X mental retardation, epilepsy and other disorders, this work could help establish how these diseases impair cortical function. In addition, results from this study may be particularly relevant for autism, which involves deficits in vibrotactile processing, and whose brain circuit basis may be revealed by studying defects in S1 processing in rodent models.