Dissociable effects of reward and navigation history on forward and reverse replays

Abstract

Sequential firing of hippocampal place cells during navigation is replayed in forward and reverse directions during sleep and awake immobility. Currently, functional roles of and factors influencing forward and reverse replays are not clearly understood. We trained rats in a spatial sequence memory task and examined effects of reward and navigation history on forward and reverse replays of CA1 place cells during awake immobility. Reward enhanced both forward and reverse replays, but in different ways. Reward increased reactivation fidelity of forward replays while increasing the rate of reserve replays. In addition, reactivation was stronger for place cell sequences associated with future than past rewarding trajectories in forward, but not reverse, replays. Our results show differential effects of reward and navigation history on forward and reverse replays, and support the proposed role of forward replays in planning future navigation.