The limbic system of the rat brain contains neurons known as head- direction cells. These cells behave like a compass, firing action potentials only when the rat's head faces in a specific direction. The objective of this proposal is to investigate the neural mechanisms of the limbic head-direction system in rats, by combining single-unit recording experiments and computational modeling. Evidence has shown that limbic structures play an important role in learning and memory. Damage to the limbic system has been associated with the symptoms of aging, stroke, Alzheimers disease, Wernicke-Korsakoff syndrome, and epilepsy. Although much is known about the cognitive effects of limbic damage, very little is known about how specific types of information are processed in limbic structures. There are several reasons why the rat head-direction system provides a good model for studying limbic information processing. First, head-direction cells are found in several major limbic structures. Second, the behavior of head direction cells is easy to measure and understand, making it possible to observe individual neurons in limbic areas as they perform an identifiable task. Finally, head-direction cells are known to be influenced by specific sensory information, so they provide a concrete example for studying how limbic structures integrate complex information from different sensory modalities, in order to form new representations of the surrounding environment.