When we fall asleep, our brains don’t just shut off; they get to work. One of their primary jobs is memory consolidation—sorting through the events of the day and filing them into long-term storage. The brain does this by spontaneously “reactivating” or replaying memories.

Recent memories are consolidated during sleep by spontaneous reactivation. However, whether and how memory reactivation affects sleep dynamics remain unclear. By tracking and modulating memory activity during sleep in mice, we revealed that negative memory reactivation promoted arousal, whereas positive memory supported sleep stability. This regulation was mediated by the reactivation of experience-specific hippocampus-amygdala engram circuits during sleep. In chronic stress models, negative memory reactivation promoted sleep disturbance, and targeted suppression of memory reactivation restored normal sleep. Our findings establish a memory-dependent sleep regulation in which memory reactivation engages downstream circuits responsive to specific memory content.