Memories are encoded in neural ensembles during learning^1,2,3,4,5,6 and are stabilized by post-learning reactivation^{7,8,9,10,11,12,13,14,15,16,17}. Integrating recent experiences into existing memories ensures that memories contain the most recently available information, but how the brain accomplishes this critical process remains unclear. Here we show that in mice, a strong aversive experience drives offline ensemble reactivation of not only the recent aversive memory but also a neutral memory formed 2 days before, linking fear of the recent aversive memory to the previous neutral memory. Fear specifically links retrospectively, but not prospectively, to neutral memories across days. Consistent with previous studies, we find that the recent aversive memory ensemble is reactivated during the offline period after learning. However, a strong aversive experience also increases co-reactivation of the aversive and neutral memory ensembles during the offline period. Ensemble co-reactivation occurs more during wake than during sleep. Finally, the expression of fear in the neutral context is associated with reactivation of the shared ensemble between the aversive and neutral memories. Collectively, these results demonstrate that offline ensemble co-reactivation is a neural mechanism by which memories are integrated across days.

记忆在学习过程中被编码在神经集合中^1,2,3,4,5,6，并通过学习后的重新激活而稳定^{7,8,9,10,11,12,13,14,15,16,17}。将最近的经历整合到现有的记忆中可以确保记忆包含最近可用的信息，但大脑如何完成这一关键过程仍不清楚。在这里，我们表明，在小鼠中，强烈的厌恶体验不仅会驱动最近的厌恶记忆的离线集合重新激活，还会驱动 2 天前形成的中性记忆的离线集合重新激活，将对最近厌恶记忆的恐惧与之前的中性记忆联系起来。恐惧特别地回顾性地联系在一起，而不是前瞻性地与不同日子的中性记忆联系起来。与以前的研究一致，我们发现最近的厌恶记忆集合在学习后的离线期间被重新激活。然而，强烈的厌恶体验也会增加离线期间厌恶和中性记忆合奏的共同重新激活。集合共激活在觉醒期间比在睡眠期间发生得更多。最后，在中性语境中恐惧的表达与厌恶和中性记忆之间共享集合的重新激活有关。总的来说，这些结果表明，离线集成共激活是一种神经机制，通过该机制，记忆在几天内被整合。