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Reward bias in the representation of space by the rodent hippocampus

Kenway Louie and Matthew A. Wilson

Center for Learning and Memory
RIKEN-MIT Neuroscience Research Center
Department of Biology
Department of Brain and Cognitive Sciences
Massachusetts Institute of Technology

While there is considerable evidence that the hippocampus is essential for memory formation, the neural processes that underlie information extraction, representation, and storage in the hippocampus are not well understood. We recorded simultaneously from many hippocampal neurons as rodents traversed a spatial environment, and characterized whether a previous history of food reinforcement at particular locations could bias the hippocampal representation of space. We found that the hippocampus exhibits increased activity at previously reinforced versus nonreinforced locations, and that this population bias reflects a reinforcement bias across a subpopulation of cells. These results suggest that the hippocampal cognitive map encodes a spatial representation weighted by behavioral relevance rather than a strict allocentric representation of the environment. A similar bias may influence the selective reactivation of hippocampal traces during post-behavior sleep, and may be important for the temporally-structured REM sleep reactivation of awake activity.