Effects of novelty and temporal distance on post-experience reactivation of hippocampal place cells encoding multiple environments

The hippocampus plays a crucial role in consolidating episodic memories from diverse experiences that encompass spatial, temporal, and novel information. This study analyzed the spike patterns of hippocampal place cells in the CA3 and CA1 areas of rats that sequentially foraged in five rooms, including familiar and novel rooms, followed by a rest period. Across multiple rooms, the generation of place fields by CA1 place cells was coordinated with other place cells. In the subsequent rest period, CA3 place cells that encoded novel environments exhibited stronger and more coordinated reactivation during sharp wave ripples (SWRs) than CA1 place cells. In contrast, CA1 place cells that encoded more recent environments exhibited stronger SWR-associated reactivation, independent of spikes of other cells, with weaker influences from novelty compared to CA3 place cells. These results suggest that post-experience SWR-associated reactivation of CA3 and CA1 neurons primarily processes novelty-related and temporal distance-related aspects of memory, respectively.