Hippocampal spiking sequences encode external stimuli and spatiotemporal intervals, linking sequential experiences in memory, but the dynamics controlling the emergence and stability of such diverse representations remain unclear. Using two-photon calcium imaging in CA1 while mice performed an olfactory working-memory task, we recorded stimulus-specific sequences of “odor-cells” encoding olfactory stimuli followed by “time-cells” encoding time points in the ensuing delay. Odor-cells were reliably activated and retained stable fields during changes in trial structure and across days. Time-cells exhibited sparse and dynamic fields that remapped in both cases. During task training, but not in untrained task exposure, time-cell ensembles increased in size, whereas odor-cell numbers remained stable. Over days, sequences drifted to new populations with cell activity progressively converging to a field and then diverging from it. Therefore, CA1 employs distinct regimes to encode external cues versus their variable temporal relationships, which may be necessary to construct maps of sequential experiences.

海马尖峰序列编码外部刺激和时空间隔，将记忆中的连续经历联系起来，但控制这种不同表征的出现和稳定性的动力学仍不清楚。当小鼠执行嗅觉工作记忆任务时，我们在 CA1 中使用双光子钙成像，记录了编码嗅觉刺激的“气味细胞”的刺激特异性序列，以及编码随后延迟的时间点的“时间细胞”。在试验结构变化和数天内，气味细胞被可靠地激活并保持稳定的场。时间细胞表现出稀疏和动态的场，在这两种情况下都重新映射。在任务训练期间，而不是在未经训练的任务暴露中，时间细胞集合的大小增加，而气味细胞数量保持稳定。几天后，序列漂移到新的群体，细胞活性逐渐收敛到一个区域，然后又从它发散。因此，CA1 采用不同的机制来编码外部线索及其可变的时间关系，这对于构建顺序体验的地图可能是必要的。