Independent Codes for Spatial and Episodic Memory in Hippocampal Neuronal Ensembles

TLDR

Hippocampal neurons were recorded while varying the chamber’s appearance but keeping its location constant, and also while encountering the same chamber in different places. The study found that hippocampal ensembles exhibited two distinct pattern‑separation modes: when cues varied but place was constant, firing rates fluctuated while spatial firing remained fixed, whereas when place varied but cues were constant, both firing rates and spatial locations changed, yielding statistically independent population vectors that could support simultaneous spatial and episodic memory representation.

Abstract

Hippocampal neurons were recorded under conditions in which the recording chamber was varied but its location remained unchanged versus conditions in which an identical chamber was encountered in different places. Two forms of neuronal pattern separation occurred. In the variable cue-constant place condition, the firing rates of active cells varied, often over more than an order of magnitude, whereas the location of firing remained constant. In the variable place-constant cue condition, both location and rates changed, so that population vectors for a given location in the chamber were statistically independent. These independent encoding schemes may enable simultaneous representation of spatial and episodic memory information.