A Manifold of Spatial Maps in the Brain

This chapter explores how space is represented in the hippocampus and entorhinal cortex of the rat brain by a manifold of rapidly interacting maps generated in conjunction by functionally specific cell types such as place cells and grid cells. Place cells are hippocampal pyramidal cells that fire when the animal is at specific positions in the environment. The brain can read out the activity of a local population of place cells to determine the position of the rat in the box. Grid cells are characterized by multiple firing locations that, in an open-field arena, collectively form a hexagonal grid over the entire space available to the animal. An alternative way to represent such environments is to use a stack of maps where each subdivision of the environment has its own representation. Several models have proposed that spatial environments are stored as large numbers of independent fragments or reference frames. The proposed multiplicity of the hippocampal-entorhinal map has received experimental verification. First, the presence of independent maps was supported by the fact that hippocampal place cells can undergo complete remapping even after small changes in the location or nature of the spatial environment.