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A grid cell is a type of neuron found in the entorhinal cortex (EC) that fires strongly when an animal is in specific locations in an environment. Grid cells were discovered in 2005 and it is hypothesized that a network of these cells constitute a mental map of the spatial environment (Hafting et al., 2005).
Grid cells are found in the dorsocaudal part of medial entorhinal cortex in rats. Cells that are located more ventral (more distant from the postrhinal border) have wider firing fields and correspondingly greater spacing between the fields.
While cells with this firing pattern are found in all layers of EC, layer II has cells that are most grid-like, independent of the head direction of the animal. As one proceeds to deeper layers, grid cells show increasing dependence on head direction (i.e. in EC layer V there are cells with a grid-like pattern that fire only when the animal is facing a particular direction).
It has been suggested that a place code is computed in the entorhinal cortex and fed into the hippocampus, which may make associations between place and events which is needed for the formation of memories.
In contrast to a hippocampal place cell, a grid cell has multiple firing fields, with regular spacing, which tesselate the environment in a hexagonal pattern. The grid cells are anchored to external landmarks, but persist in darkness, suggesting that grid cells may be part of a self-motion based map of the spatial environment.
- Fyhn M, Molden S, Witter MP, Moser EI, and Moser MB. Spatial representation in the entorhinal cortex. Science 305, 1258-64 (2004).
- Hafting T, Fyhn M, Molden S, Moser MB, and Moser EI. Microstructure of a spatial map in the entorhinal cortex. Nature 436, 801-6 (2005).
- Sargolini F, Fyhn M, Hafting T, McNaughton B, Witter MP, Moser EI, and Moser MB. Conjunctive representation of position, direction, and velocity in entorhinal cortex. Science 312, 758-62 (2006).