What is stored in the hippocampus during a tactile categorization task?

To understand how sensory experiences are stored in the brain, we examined neuronal fi ring in hippocampus during tactile behavior. Rats learned to associate stimulus texture with reward location; multiple textures were associated with the same reward location and thus formed a behavioral category. Rapid fi ring rate modulation carried texture identity information (10% of neurons), free from spatial and behavioral confounds; slow fi ring rate modulation carried behavioral category information (63% of neurons). Category information appeared during texture contact, simultaneous with an increase in theta power in the local fi eld potential; it persisted or recurred during reward collection, when theta power was suppressed and “reward neurons” (8%) fi red. Reward-triggered recurrence of category information could be a mechanism to link stimulus, action, and outcome when separated in time.