Title: How reward expectation influences memory representations in the hippocampus
Reward expectation strongly influences learning and memory. Hippocampal place cells support spatial memories through a map that over-represents reward locations, but how maps are influenced during changes in reward expectation and the circuit mechanisms involved are unclear. We show that extinction of reward expectation in mice eradicates place cell over-representation of rewards and causes ~35% of place fields to be lost and ~10% to remap throughout the environment. The remaining impoverished map is unreliable and poorly decodes position, even though mice remain aware of their position and their arousal state is unchanged. Inhibition of Ventral Tegmental Area (VTA) dopaminergic neurons mimics many of the effects of reward expectation extinction and VTA axons in CA1 exhibit a reward-proximity signal that is dependent on reward expectation. We conclude that changes in reward expectation rapidly transforms CA1 encoding of environments partially driven by VTA, likely through modulation of a VTA-CA1 reward-proximity signal – providing a mechanism by which reward expectations can influence hippocampal memories. This also supports the idea that the hippocampus does not just encode space, but rather uses a multidimensional code to encode a variety of behaviorally relevant relational information.
Dr. Sheffield is an Assistant Professor of Neurobiology at the University of Chicago.
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