Sleep cycles process memories

Memory replay during sleep probably facilitates the transfer of memories from intermediate storage in the hippocampus to long-term storage in the cortex. In a paper published in Neuron, Bollmann, Baracskay et al. reveal that memories are not static during this process, but are instead transformed into their long-term state during the sleep period. The authors tracked spatial memory ensembles in the hippocampus of rats across acquisition, a prolonged (17–20 h) sleep/rest period and recall the following day. Acquisition and recall induced distinct neuronal ensembles, and ensemble activity gradually evolved from an acquisition-like to a recall-like state during sleep. Interestingly, non-REM sleep pushed memory drift towards recall, whereas REM sleep counteracted this drift. These findings echo prior work that indicated a crucial role for non-REM sleep in consolidation and also offer intriguing clues regarding the potentially distinct roles of non-REM and REM sleep in this process.

Original reference: Neuron https://doi.org/10.1016/j.neuron.2025.02.025 (2025)