Firing Fields of Dorsocaudal Medial Entorhinal Cortex as a Context-Independent Spatial Map

Abstract

The firing fields of the ?rid cells?found in the rat dorsocaudal medial entorhinal cortex (dMEC) present a surprising pattern of context-independent regularity. We use computational means to analyze and validate the geometric and algebraic invariant properties of the firing fields, leading to a context invariant spatial map. Our method computes the specific symmetry group implicitly associated with the spatial map, and quantifies the regularity of the firing fields to achieve a symmetry-based clustering of two different types of ?rid cells.?This quantified regularity makes spatial mapping more computationally efficient and suggests a way to use the dMEC firing patterns to estimate the probabilty of the rat being located at different points in the room. Finally, general properties of context-independent population codes are suggested. Namely, context-independent population codes gain robustness by introducing uncertainty and ambiguity.