PLASTICITY OF BARREL FIELD INTRACORTICAL CIRCUITRY

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DESCRIPTION (provided by applicant): The goal of the proposed research is to understand how tactile experience with the whiskers modifies the receptive field (RF) of neurons in the septa around cortical barrels, and what role septal neurons play in sensory processing and cortical plasticity. Anatomically, layer IV barrel neurons project horizontally into the septa surrounding the barrels and vertically above the barrel to layers II+III in a cap-like pattern that overlaps around each barrel. In contrast to barrels, which are dominated by specific thalamic VPM inputs, septal neurons are the cortical target of less dense inputs from the thalamus and commissural inputs from the contralateral cortex. When two whiskers are stimulated nearly simultaneously, some cells in the septum show increased (facilitated) responses. If there is a delay of 20-50 ms between whisker stimuli, the response to the second whisker is inhibited in barrel cells, but not studied in septal cells in relation to their location. We propose that the septa are specialized regions for modifying cortical responses to inputs that are generated by several vibrissa. Our main hypothesis is that the topography in the septal regions provides a distributed cell matrix in which the strength of whisker inputs is compared and modified through use-dependent, intracortical connection plasticity. We propose that septal cells operate as sensory information modulators in that they integrate the activity of several barrels and feed back reciprocally to modify barrel RF's. We will test the notion that septal cells contribute strongly to experience-driven modifications of barrel cell responses using a test for plasticity that we developed, called "whisker pairing plasticity". Specifically, we wish to define the role of whisker experience in determining adult septal cell plasticity to show how use-dependent plasticity is developmentally regulated. Analysis of these characteristics of the septal cells will provide significant new information about sensory processing in the barrel field cortex. The results will generate a better understanding of how sensory activity modifies the RF of cortical neurons throughout life, and the experiments will specify integrative deficits that are produced in septal neurons by inadequate early sensory experience (sensory deprivation).