Persistence of neuronal representations through time and damage in the hippocampus

It is not known how neurons encode memories that can persist up to decades. To investigate this question, we performed simultaneous bilateral imaging of neuronal activity in the mouse hippocampus over weeks. From one day to the next ∼40 % of neurons changed their responsiveness to cues; however, thereafter only 1 % of cells changed for each additional day. Despite the apparent instability between days, field responses of CA1 neurons are very resilient to lack of exposure to the task or lesions to CA1. Although a small fraction of individual neurons retain their responses over weeks, groups of neurons with inter- and intrahemispheric synchronous activity had stable responses. Neurons whose activity was synchronous with a large group of neurons were more likely to preserve their responses across multiple days. These results suggest that although information stored in individual neurons is relatively labile, it is very stable in networks of synchronously active neurons. One Sentence Summary Neuronal representations in networks of neurons with synchronized activity are stable over weeks, even after lack of training or following damage.