Long‐term spatial memory is maintained despite ongoing changes in hippocampal representations

The long-term persistence of memory is thought to depend on the stability of its underlying neuronal representation. However, this relationship has not been measured over timescales of weeks. To address this question, we longitudinally imaged large neuronal populations in the hippocampus CA1 of freely-behaving mice as they learned a novel maze, and weeks later during memory recall. Hippocampal representation of the maze was highly-dynamic despite stable long-term spatial memory, and we found no relationship between memory performance and the long-term stability of the place code. Additional training led to rapid reinstatement of spatial memory performance, but place codes did not converge back to those established during learning but rather continued to change. Thus, spatial memory content is reliably preserved over weeks without relying on the long-term stability of hippocampal representations. None