The hippocampal formation is central for the learning and consolidation of memories. While it is known that high-frequency oscillations, called sharp wave ripples (SWRs), play a critical role for memory consolidation, it is unclear if they interact with engram cells. We evaluated the interaction of these oscillations with engram cells as mice explored two environments over several days and found that hippocampal reactivation after learning is biased to memory engram cells composed of both principal cells and interneurons. Our findings reveal a critical link between cellular and network mechanisms for memory formation and imply that interneurons play a key role in it.