DURATION OF DAILY EXPERIENCE GATES THE TRANSITION FROM DRIFTING TO STABLE HIPPOCAMPAL MEMORY CODES

Learning in a constant environment requires hippocampal circuits to convert novelty-driven exploration into stable representations. Longitudinal studies show CA1 activity can stabilize or drift across days, but which experience features set this balance is unclear. We tested whether daily session duration drives the transition from labile to stable hippocampal codes. We used longitudinal miniscope calcium imaging in CA1 as C57BL/6 mice explored the same open field for four days. Animals completed daily 10, 30, or 60 min sessions. We tracked position and behavior and identified neurons selective for spatial location (place cells) and non-spatial variables: acts, head/body direction, zones, and object events. Across conditions, many active CA1 neurons were feature-selective, consistent with a multidimensional representation of ongoing experience. However, the stability of the spatial code depended strongly on session duration. During 10-min exposures, place cells were initially prominent but their fraction decreased across days, and spatial selectivity showed pronounced day-to-day drift with no cells maintaining place selectivity across all four sessions. In contrast, during 30- and 60-min exposures the proportion of place cells remained high across days, and a substantial subset preserved stable place selectivity throughout the entire four-day series. Non-spatial selectivity was consistently present across days and durations, with zone-, direction-, locomotion-, and object-related selective neurons persisting without a monotonic decline. These results indicate that extending daily experience promotes a shift from drifting to stable hippocampal memory codes while preserving non-spatial components that may scaffold episode-like representations. Supported by the Non-commercial Foundation for Support of Science and Education “INTELLECT”.