MODULATION OF NEURAL SYSTEMS IN LEARNING AND MEMORY

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Largely on the basis of lesion studies, different neural systems appear to be responsible for learning and remembering different classes of information. However, most learning experiences contain information that crosses the classes served by these distinct neural systems. The main goal of this project is to determine whether modulators of memory processing regulate the relative participation of different brain systems during learning, thereby regulating what different rats learn in those situations. The proposed experiments use direct brain injections of glucose and morphine, together with in vivo microdialysis/HPLC measures of acetylcholine output, to study learning and memory in rodents. Three tasks and three brain areas will be tested: conditioned place preference learning, amygdala-dependent; place learning, hippocampus-dependent; response learning, striatum-dependent. The first set of experiments uses direct injections of glucose and morphine, treatments which enhance and impair learning and memory processes where injected. Because each of the anatomical systems can at times interfere with learning by another system, some predictions include apparently paradoxical impairment and enhancement of learning by appropriate injections of glucose and morphine. The second set of experiments determines whether training-related increases in acetylcholine are restricted to those neural systems activated by different training procedures. Included is one task in which rats can learn using either of two strategies. Because each strategy is likely to require major participation by a different neural system, measures of acetylcholine output in each system during training might reveal what an individual rat is learning, i.e. which strategy it employs during learning. The third set of experiments determines whether glucose enhancement of learning and memory is accompanied by augmented acetylcholine release only in the neural system activated by specific training. The findings of these experiments may lead to a new view of how modulators of memory regulate the relative participation of different memory systems during learning.