Memory formation and maintenance involve a constant tension between stability andchange. On one hand, stable representations are essential for preserving past experiences.On the other hand, memories must remain flexible to incorporate new information andreflect the evolving world. Thus, while memory resists interference to maintain invariance, itmust also reorganize to enhance efficiency and adapt to novel experiences.In this lecture, I will discuss one to three studies examining this balance within thehippocampal spatial representation system. First, regarding representational drift, spatialrepresentations in the hippocampus gradually change with experience. Our findings suggestthat such changes are driven more by ongoing experience than by forgetting. Second, inexploring environmental mapping, we find that the subiculum encodes differently shapedrooms with strikingly similar activity patterns, hinting at an invariant, latent representation ofspatial structure. Third, we investigate a flashbulb memory–like effect, observingpronounced hippocampal activity changes following salient life events in mice.Together, these projects illustrate how the hippocampus negotiates the trade-off betweenpreserving established memories and accommodating new experiences.
