Locus coeruleus functional modulation of the hippocampal complex: Behavior and physiology

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Using animal research, scientists have been able to reveal how hippocampal neurons produce a representation of space, i.e., spatial maps. Our hypothesis is that spatial maps enable us to separate memories and behave appropriately in different locations. Obviously, we need spatial memories to call up the behaviors required for tasks at home, at work and in many other contexts. Our ability to behave flexibly depends on connecting behaviors with locations. Navigational information helps us to identify places. Also, we may believe a place is different if we see a different shape to the walls, or hear new sounds, or smell new smells. A small group of cells in the brain, the locus coeruleus, is known to signal changes or novelty, sending a novelty signal to the hippocampus and other parts of the brain. These novelty signals may cause hippocampal maps to change, and thus permit new, and even contradictory, behaviors to occur in similar spaces. A recently developed method allows the direct visualization of hippocampal spatial maps at two different times. We predict that the more different two spatial maps are, the easier it will be for animals to change their behavior in two similar environments. An artificial novelty signal will be introduced to see if it makes maps different and whether it makes memories of altered spaces stronger. These studies will illuminate how representations of location are formed and whether they play a role in supporting adaptive behavior by separating memories. Our research has implications for understanding the operation of two brain areas, the hippocampus and the locus coeruleus that are the first to deteriorate in Alzheimer's disease. This could help us understand how to support and enhance memory and adaptive behavior, generally.