In rats and some other rodents layer IV of the first somatic sensory (SmI) cortex contains multi-cellular cytoarchitectonic units called barrels, which receive a one-to-one projection from the large facial vibrissae, or whiskers, on the contralateral face. Because of this distinctive structural organization, the barrel cortex has received considerable attention anatomically but to date comprehensive ways of providing functional input to this cortex and of activating neurons there have not been adequately explored. The proposed research will examine in detail the functional organization of this cortex in normal rats focusing on the integrative properties of cortical neurons revealed by stimulation of two or more vibrissae. Microelectrodes will be used to study the extracellular responses of single cortical vibrissa units to controlled sensory stimulation of the vibrissae produced by an array of independently controllable electromechanical stimulators which I have recently developed. Data, which will be collated with computer assistance, will be interpreted with respect to barrel and laminar boundaries. In some cases morphological and functional data will be directly correlated using intracellular recordings and dye injections.