SPATIAL FUNCTIONS OF THE MEDIAL TEMPORAL LOBE

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How do medial temporal lobe structures contribute to memory? Finding the answer to this question is a long-term goal of neuroscience research. Recent findings from neuroanatomical, behavioral and functional imaging studies have provided new insight into the potential functions of two of these medial temporal lobe structures, the perirhinal and parahippocampal cortices. These findings suggest that like the hippocampal formation, these cortical medial temporal lobe areas may also contribute importantly to spatial functions. To address this possibility, proposed research combines the use of sensitive neuroanatomical tracing techniques and single-unit neurophysiological techniques to explore the role of the perirhinal and parahippocampal cortices in two aspects of spatial function: spatial representation and spatial memory. Anterograde tracing techniques will be used to define the regional and laminar topography of parahippocampal inputs arising from "dorsal stream" structures involved in processing stimulus location. Single unit physiological techniques will be used to define the kinds of spatial and mnemonic information carried by neurons in the perirhinal and parahippocampal cortices as animals perform a delayed match to place task. These experiments will also define the spatial frame of reference of the place-selective neurons in these areas. A separate task will be used to examine the role of perirhinal and parahippocampal neurons in the formation of new long-term memories for spatial information. Neural activity will be recorded as monkeys learn the spatial locations of particular rewarded targets in the context of a set of complex visual "scenes". Analyses will be directed at identifying any "tuning" of neural activity associated with learning these new, long-term location-scene associations. Because memory for spatial information plays such a prominent role in human episodic (i.e. event) memory, findings from these studies may also serve to establish links between experimental work in monkeys and current work on the brain basis of memory in humans.