This study investigates the long-term dynamics of CA1 hippocampal place codes in freely behaving mice. The researchers used Ca2+-imaging to track the place fields of thousands of CA1 pyramidal cells over 45 days as the mice repeatedly explored a familiar environment. They found that place coding was dynamic, with each day involving a unique subset of cells. However, cells within a 15-25% overlap between any two subsets retained the same place fields, which ensured an accurate spatial representation across weeks. The study also revealed that the stability of place fields was not influenced by cell physiological or coding parameters, but rather by network dynamics. Bayesian decoding techniques showed that the ~15-25% overlap in place-coding ensembles across days was sufficient to reconstruct the mouse's trajectory with high accuracy, even for 30-day intervals. These findings suggest that CA1 place cells retain spatial information through stable place field locations and a moderate overlap in coding ensembles, while also allowing for distinct memory traces of different events in the same environment.This study investigates the long-term dynamics of CA1 hippocampal place codes in freely behaving mice. The researchers used Ca2+-imaging to track the place fields of thousands of CA1 pyramidal cells over 45 days as the mice repeatedly explored a familiar environment. They found that place coding was dynamic, with each day involving a unique subset of cells. However, cells within a 15-25% overlap between any two subsets retained the same place fields, which ensured an accurate spatial representation across weeks. The study also revealed that the stability of place fields was not influenced by cell physiological or coding parameters, but rather by network dynamics. Bayesian decoding techniques showed that the ~15-25% overlap in place-coding ensembles across days was sufficient to reconstruct the mouse's trajectory with high accuracy, even for 30-day intervals. These findings suggest that CA1 place cells retain spatial information through stable place field locations and a moderate overlap in coding ensembles, while also allowing for distinct memory traces of different events in the same environment.