# Single‐Field Evolution Rule Governs the Dynamics of Representational Drift in Mouse Hippocampal Dorsal CA1 Region

## TL;DR

The study reveals a rule governing how place fields in the mouse hippocampus evolve over time, linking individual field activity to overall brain representation changes.

## Contribution

The novelty is the identification of a Single-Field Evolution Rule (SFER) that governs place field dynamics independently of novelty or decision-making.

## Key findings

- Active place fields are more likely to persist, while inactive ones decline.
- SFER-based models best predict field evolution and capture coordinated multi-field changes.
- Population-level stabilization emerges from the SFER despite its novelty-irrelevance.

## Abstract

Hippocampal place codes change substantially across days, yet the mechanisms governing their temporal evolution remain incompletely understood. To quantitatively characterize this process, longitudinal one‐photon calcium imaging of dorsal CA1 neurons in mice is performed for up to 56 days across multiple goal‐oriented navigation tasks. Parallel to mice's improvements in maze learning and navigational performance, thousands of place fields exhibit complex evolutionary trajectories characterized by formation, disappearance, and retention. Leveraging statistical analyses and sequential learning models (e.g., recurrent neural networks and hidden Markov models), a position‐, decision‐making‐, and novelty‐irrelevant Single‐Field Evolution Rule (SFER) is identified: active states of a place field increase its probability of remaining active in the subsequent session, whereas inactive states reduce it. Simulations of a stochastic discrete dynamical system defined by SFER reveal that the novelty‐related stabilization of dCA1 place codes at the population level emerges as a collective outcome of the novelty‐irrelevant SFER. Among the ten tested models, SFER‐based models provide the best predictions of field evolutions, and an extended version incorporating inter‐field interactions and day‐to‐day fluctuations effectively captured coordinated multi‐field evolution. This framework offers a novel, efficient, and parsimonious approach that demonstrates the derivational relationship between activity‐dependent single‐field evolution and population‐level drift dynamics in the hippocampus.

Long‐term hippocampal place‐code dynamics are investigated using calcium imaging across weeks of maze navigation. Analyses reveal a novelty‐irrelevant Single‐Field Evolution Rule (SFER), where active fields promote persistence and inactive fields decline. Simulations demonstrate that novelty‐related stabilization of population codes emerges from this rule. This framework provides a parsimonious explanation linking single‐field activity to collective drift in hippocampal representations.