The objective of the proposed research is the analysis of a novel form of long-term potentiation recently discovered in olfactory cortex. This potentiation is induced by repeated high-frequency stimulation of the olfactory bulb or of association fibers in olfactory cortex, and is manifested as a selective long-term potentiation of late components in potentials evoked in the olfactory cortex and olfactory bulb. Previous research indicates that this potentiation is very long-lasting and is dependent upon activation of NMDA receptors for its induction. Evaluation of available evidence supports the hypothesis that this potentiation reflects enhanced transmission at the synapses made by cortical association fibers upon inhibitory neurons in the olfactory cortex and olfactory bulb. The proposed research will explore the functional significance of this potentiation and test the hypothesis outlined above using evoked potential and single-cell recording techniques and a current source-density analysis in freely-moving and urethane-anesthetized rats. These techniques will be used to address the following issues: a) the identity of the specific synapses that undergo potentiation; b) the effect of this potentiation on the response of principal neurons in the olfactory cortex and olfactory bulb to activation of afferent and cortical association fibers, c) the relationship of this potentiation to other forms of functional plasticity known to occur in olfactory cortex, and d) the circumstances under which this potentiation is most likely to occur naturally. The outcome of this research should provide insight into how synapses in the olfactory cortex and olfactory bulb are modified by experience and how this modification affects patterns of activity within these two areas and interactions between them. This in turn should aid in understanding the mechanisms of information processing, storage, and retrieval in the olfactory forebrain and, by extension, contribute to the understanding and eventual treatment of olfactory disorders.