Andreas Herz: Andreas Herz: Decoding Grid Cells for Spatial Navigation

Abstract

Mammalian grid cells fire when an animal crosses the points of an imaginary hexagonal grid tessellating the environment. Following an introduction to spatial codes in the rodent hippocampal formation, I will show how animals can navigate by reading out a simple population vector of grid cell activity across multiple spatial scales, even though neural activity is intrinsically stochastic.

This theory explains why grid cells are organized into discrete modules within which all cells have the same lattice scale and orientation. The lattice scale changes from module to module and should form a geometric progression with a scale ratio of around 3/2 to minimize the risk of making large-scale errors in spatial localization. Such errors should also occur if intermediate-scale modules are silenced, whereas knocking out the module at the smallest scale will only affect spatial precision. For goal-directed navigation, the allocentric grid-cell representation can be readily transformed into the egocentric goal coordinates needed for planning movements. The goal location is set by non-linear gain fields that act on goal vector cells.

This theory illustrates the benefits of multi-scale periodic representations of physical space, where the outside world's flat Euclidean geometry is curled up into a torus.

About the speaker and his research

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