The Statistical Structure of the Hippocampal Code for Space as a Function of Time, Context, and Value.

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Cell. 2020 Oct 29;183(3):620-35. doi: 10.1016/j.cell.2020.09.024

The Statistical Structure of the Hippocampal Code for Space as a Function of Time, Context, and Value. Lee (Albert) LabRomani Lab

Lee JS, Briguglio JJ, Cohen JD, Romani S, Lee AK

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Abstract

Hippocampal activity represents many behaviorally important variables, including context, an animal's location within a given environmental context, time, and reward. Using longitudinal calcium imaging in mice, multiple large virtual environments, and differing reward contingencies, we derived a unified probabilistic model of CA1 representations centered on a single feature-the field propensity. Each cell's propensity governs how many place fields it has per unit space, predicts its reward-related activity, and is preserved across distinct environments and over months. Propensity is broadly distributed-with many low, and some very high, propensity cells-and thus strongly shapes hippocampal representations. This results in a range of spatial codes, from sparse to dense. Propensity varied ∼10-fold between adjacent cells in salt-and-pepper fashion, indicating substantial functional differences within a presumed cell type. Intracellular recordings linked propensity to cell excitability. The stability of each cell's propensity across conditions suggests this fundamental property has anatomical, transcriptional, and/or developmental origins.