DESCRIPTION: The long term goal of the project is to elucidate the neural circuit mechanisms underlying the immediate sensory reorganization of subcortical and cortical sensory maps induced by local anesthesia (e.g. dental anesthesia) of the face. We refer to this as "acute plasticity). The working hypothesis is that adult somatosensory representations are not "hard-wired," but instead are defined by dynamic and distributed interactions between feed-forward and feedback projections which converge on neurons located at all processing levels of the somatosensory system. According to this hypothesis, lesions at any part of the sensory system should induce an immediate reorganization across all subcortical nuclei and cortical areas that belong to the system. We will test the hypothesis by investigating the role of cortical feedback projections in the concurrent reorganization process observed in multiple thalamic and brainstem nuclei after a subcutaneous injection of the local anesthetic lidocaine. Simultaneous recording of up to 135 single brainstem, thalamic and cortical neurons will be made in the same rat while its somatosensory cortex is reversibly inactivated before, during and after the induction of reversible peripheral deafferentation. This approach will allow us to establish correlations between concurrent reorganizations occurring at each level and to quantify the effects of cortical inactivation on this process. The prediction is that cortical inactivation will reduce the spatiotemporal extent of the subcortical reorganization and that this effect will be proportional to the density of cortical feedback converging in each subcortical nucleus. These experiments will provide fundamental information concerning the circuit mechanisms that underlie the genesis of sensory representations and their ability to be shared by experience, two central areas of investigation in modern neuroscience.