In this sentence the positions of “D1” and “D2” are reversed, an error that has now been corrected in the article online. “
“An animal’s position in the local environment is monitored by a spectrum of functionally
specific cell types in the hippocampus and the adjacent parahippocampal areas, particularly the MEC. In the hippocampus, place cells fire selectively when the animal visits one or a few specific locations of the local environment (O’Keefe and Dostrovsky, 1971). In the MEC, grid cells fire at multiple locations that, for each cell, define a hexagonal grid that tessellates the entire space available to the animal (Hafting et al., 2005). Although the majority of cells in superficial MEC layers are grid cells (Sargolini et al., 2006), selleck products these cells intermingle with border cells, which fire whenever the animal comes close to one or several local geometric boundaries, such as the walls of the recording enclosure (Savelli et al., 2008 and Solstad et al., 2008). In layer III and deeper MEC layers, grid cells (Sargolini et al., 2006) also
mix with head direction cells, which fire only when the animal faces a given direction (Ranck, 1985 and Taube et al., 1990). The presence of multiple spatial cell types within the same brain system raises questions about their interrelationships. Place cells are probably generated from spatial inputs from the entorhinal cortex, the main cortical source of input to the hippocampus. The abundance of grid cells in the superficial layers Venetoclax research buy of MEC points to grid cells as a likely source for the place cell signal.
In several early models, place cell formation was explained by a Fourier mechanism in which periodic firing fields from grid cells with different grid spacing were linearly combined to generate single fields in hippocampal target neurons (O’Keefe and Burgess, 2005, Fuhs and Touretzky, 2006, McNaughton et al., 2006 and Solstad et al., 2006). This possibility has been challenged, however, by the observation that place cells mature faster than grid cells in young animals (Langston et al., 2010 and Wills et al., 2010). When rat pups until leave the nest for the first time at postnatal day 16 or 17 (P16–P17), many place cells already have sharply confined firing fields similar to those of adult animals. In contrast, grid cells are far from fully developed. Firing fields are irregular and variable in size and shape and although some spatial periodicity can be observed in some neurons, adult-like patterns do not appear until approximately 1.5 weeks later, near the age of 4 weeks. The lack of sharply confined grid outputs in the 2.5- to 4-week-old nervous system has raised the possibility that juvenile place cells receive spatial information from other functional cell populations, such as the border cells of the MEC.