Hippocampal Place Fields Maintain a Coherent and Flexible Map across Long Timescales

Abstract

To provide a substrate for remembering where in space events have occurred, place cells must reliably encode the same positions across long timescales. However, in many cases, place cells exhibit instability by randomly reorganizing their place fields between experiences, challenging this premise. Recent evidence suggests that, in some cases, instability could also arise from coherent rotations of place fields, as well as from random reorganization. To investigate this possibility, we performed invivo calcium imaging in dorsal hippocampal region CA1 of freely moving mice while they explored two arenas with different geometry and visual cues across 8days. The two arenas were rotated randomly between sessions and then connected, allowing us to probe how cue rotations, the integration of new information about the environment, and the passage of time concurrently influenced the spatial coherence of place fields. We found that spatially coherent rotations of place-field maps in the same arena predominated, persisting up to 6days later, and that they frequently rotated in a manner that did not match that of the arena rotation. Furthermore, place-field maps were flexible, as mice frequently employed asimilar, coherent configuration of place fields to represent each arena despite their differing geometry and eventual connection. These results highlight theability of the hippocampus to retain consistent relationships between cells across long timescales and suggest that, in many cases, apparent instability might result from a coherent rotation of place fields.