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Grid cells
Additional recommended knowledgeA 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). DescriptionGrid cells are found in the dorsocaudal part of medial entorhinal cortex in rats. Cells that are located more ventral (more distant from the border of entorhinal cortex with postrhinal cortex) 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 tessellate the environment in a hexagonal pattern. The unique properties of grid cells are as follows
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. Cellular ElectrophysiologyStellate cells recorded from the grid cell-containing region of entorhinal cortex in vitro have been shown to have intrinsic, subthreshold oscillations and resonant properties (Giocomo et al. 2007). When the membrane potential of such a cell is brought near threshold, the membrane potential begins to oscillate at a frequency partially dependent on how depolarized the cell is. Similarly, when current is injected into such a cell at a range of frequencies, the magnitude of the cell's response depends on the frequency of the input, with a largest magnitude of response at the resonance frequency. The oscillation and resonant frequencies of these cells decrease along the dorsoventral axis of entorhinal cortex, correlating to the changing spatial periodicity (the increasing spacing of the grid fields) along the same axis. This suggests that these temporal oscillations may relate to the spatial properties of grid cells, in agreement with a prediction from an earlier model of grid cells (Burgess et al. 2007). References
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Grid_cells". A list of authors is available in Wikipedia. |