Entorhinal grid cells and hippocampal memory
Centre for the Biology of Memory, NTNU, Trondheim , Norway
The ability to find one's way through the environment depends on the brain's ability to integrate information about location, direction and distance. This integration depends on a widespread brain network interfaced by the medial entorhinal cortex (MEC). I will show that layer II of the MEC contains a two-dimensional metric map of relative spatial location. A key component of the map is the ‘grid’ cell, which fires whenever the animal’s position coincides with the vertices of a periodic triangular grid spanning the complete surface of the environment. In layers III-VI of the MEC, grid cells intermingle with cells that are sensitive to head orientation or have conjunctive grid and head-direction properties. Co-localized grid cells operate as coherent ensembles, exhibiting synchronous shifts in firing location when rats move from one environment to another. Coherent shifts in the entorhinal map are associated with global remapping in the hippocampus. These and a number of other properties of the grid-cell network point to the MEC network as part of a universal, path-integration-based spatial metric that is independent of the specific environment.