Regular spatial grid mapping found in hippocampus
An area of the hippocampal formation (dMEC, dorsocaudal medial entorhinal cortex) contains neurons which fire when the animal is in a particular location (like hippocampal place cells), but which have a strikingly regular mapping from neurons to locations (that is, the “place field” to which each cell responds is very regular and geometric).
Torkel Hafting, Marianne Fyhn, Sturla Molden, May-Britt Moser and Edvard I. Moser. Microstructure of a spatial map in the entorhinal cortex. Nature, doi: 10.1038/nature03721.
Check out figure 1 from the paper, particularly the two rightmost columns in section (b):
The caption for parts (a) and (b) of this figure is: “a, Sagittal Nissl-stained section indicating the recording location (red dot) in layer II of the dMEC. Red line indicates border to postrhinal cortex. b, Firing fields of three simultaneously recorded cells at the dot in a during 30 min of running in a large circular enclosure. Cell names refer to tetrode (t) and cell (c). Left, trajectory of the rat (black) with superimposed spike locations (red). Middle, colour-coded rate map with the peak rate indicated. Red is maximum, dark blue is zero. Right, spatial autocorrelation for each rate map (see Supplementary Methods). The colour scale is from blue (r = -1) through green (r = 0) to red (r = 1). ”