Project Summary The way in which brain structures interact to process sensory information from the environment dictates sensory perception. Understanding the relationship whereby one sensory structure modulates information within another is critical to the way by which sensory systems, as a whole, process and encode sensory stimuli. In the mammalian olfactory system, secondary olfactory structures (also referred to as `cortical' structures), including the `primary' olfactory piriform cortex (PCX) and olfactory tubercle (OT), receive olfactory information directly from olfactory bulb (OB) sensory neurons. A unique feature of the PCX is its extensive and highly plastic association fiber system, whereby PCX pyramidal cells innervate a number of structures. The PCX association fiber system is considered essential for the ability of the brain to learn about recent olfactory experiences. Anatomical and electrophysiological studies have demonstrated that PCX association fibers innervate the OT, a subdivision of the ventral striatum, with privileged access to the basal ganglia. Whether, and if so how, the PCX modulates odor coding within the OT is entirely unknown. Further, it is also unknown if PCX input into the OT is subject to experience-dependent plasticity. Understanding the function of this pathway will yield important information into how the primary olfactory cortex (the PCX) may shape the function of a striatal structure which is greatly implicated in the neurobiology of motivated behaviors (the OT). In the proposed research, I will test the overall hypothesis that PCX inputs into the OT lead to an increase in both OT spontaneous and odor-evoked neural activity that is strengthened by olfactory learning. Both Aims will utilize opto-physiological techniques in two separate olfactory behavioral tasks to determine mechanisms whereby PCX neurons and/or PCX association fibers themselves modulate odor information processing in the OT. In Aim 1, I will determine the influence of PCX neuron and/or PCX association fiber excitation on the encoding of odors in the OT of awake animals. In Aim 2, I will use a combination of olfactory psychophysics and opto- physiology to demonstrate the modulation of association fiber strength into the OT by olfactory learning. Overall, the results of the proposed project will elucidate fundamental principles by which olfactory structures interact to modulate odor information processing in behaviorally-relevant manners.