Hippocampal astrocytic sequences emerge during learning and memory recall

The dorsal hippocampus is a heterogeneous structure with numerous cell types involved in generating and maintaining detailed representations of space and time. Although pyramidal neurons support associative memory through sequentially active 'time cells', non-neuronal contributions remain poorly understood. Here we used one-photon calcium imaging to track dorsal CA1 astrocytes across days in freely moving mice during contextual fear conditioning. Foot shock evoked robust astrocytic calcium-event sequences with a time-compressed structure that resembled time-cell activity. Similar sequences re-emerged during later exposure to the conditioned context despite the absence of shock, but were not detected in a distinct context. Within the conditioned context, spontaneous astrocytic activity was associated with transitions across behavioral states, including freezing; this relationship was absent in the new context. Together, these findings suggest that astrocytes contribute to hippocampal representations of the temporal structure of associative memories and motivate further study of how diverse hippocampal cell types jointly encode experience.