Long-term memory reorganization of navigational episodes.

During navigation, the brain builds representations of self-motion and of environmental information for future action. The classic view suggests that these representations consolidate and eventually stabilize. However, there are no data on their fate at extended memory delays. Here we investigated memory of real-world navigational episodes across memory delays of up to three decades. We show that memory of the spatial aspects of these episodes do not achieve a stable state but rather continue to transform for many years. Our data suggest that at any given point in time, spatial memory of navigational episodes is a changing combination of episode-independent schematic information and several interacting spatial representations directly related to a navigational episode, which may show distinct temporal trajectories. Consistent with recent accounts of memory reorganization, we further show that neither current theories of systems consolidation nor classic models of forgetting fully explain spatial memory performance at extended memory delays.