cfos principal cells and interneurons are strongly reactivated by sharp wave ripples

The hippocampal formation is central for the learning and consolidation of spatial memories. While it is known that the high-frequency oscillations, called sharp wave ripples, play a critical role for memory processes, it is unclear if they interact with the memory engram and spatial engram cells. Here we identify the effect of these oscillations on engram cells as mice explored two environments over several days. We found that both principal cells and interneurons are part of the cfos-tagged engram. cfos-tagged principal cells, place cells and interneurons are highly reactivated by SWRs, whereas none of the negatively SWR-modulated cells are part of the engram. Together, our findings reveal a critical link between cellular and network mechanisms for memory formation and imply that interneurons play a key role in it.