Estrogen Modulation of Learning Strategy: A Neural Systems Approach

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The goal of this project is to identify the brain areas through which estrogen acts to modulate learning and memory. The underlying hypothesis is that the effects of estrogen on learning and memory are specific to types of learning, and associated brain areas, used to solve different mazes. Two mazes that tap two different types of learning strategies, place learning and response learning, will be used to determine whether estrogen acts directly at specific discrete brain sites, the hippocampus and dorsal striatum, respectively, important for good performance in these tasks. Two experiments examine the role of estrogen on learning in rats that have had their ovaries removed, thus removing the intrinsic source of estrogen. In the first experiment, rats will receive estrogen directly into either the hippocampus or the striatum and will then be tested for place and response learning. In the second experiment, rats will receive injections of estrogen into the circulation after an estrogen blocker is administered directly into the hippocampus or the striatum, and the rats will then be tested for place and response learning. Some prior reports suggest that estrogen impairs learning and memory, while other reports indicate that estrogen improves learning and memory. The approach taken in this proposal may clarify the basis for these conflicting reports by showing that both conclusions are correct. Estrogen might activate or inhibit different brain areas, thereby changing the learning strategy used and thus what and not necessarily how much is learned under different hormone conditions. The basic finding that estrogen's effects on learning strategy are governed by different neural systems will prove useful for understanding the neural and cognitive processes that accompany the decline in hormones with menopause.