Grid cells in the mEC are believed to be part of the neural apparatus that performs path integration; updating an animal's representation of location using self motion cues. In line with this view the metric provided by grid cells, their spatial scale, is thought to be a fixed constant. We recorded grids from rats as they first explored previously unvisited environments and on subsequent visits to those environments as they became familiar. On first exposure to the novel environments grid firing fields were both less regular and of a larger scale than in a very familiar environment. With subsequent exposures on the same day and on following days, grids in the novel environments became more regular and shrank in scale such that they approached the same scale as grids in the very familiar environment. Grid expansion was accompanied by a reduction in theta frequency measured from the EEG and was also inversely correlated with a reduction in intrinsic firing frequency estimated from the spike train of each cell. These results provide support for the oscillatory interference model of grid cell firing and question the putative role of grid cells in path integration, at least in unfamiliar environments. Furthermore, grid expansion may induce a mismatch with other spatial inputs and so potentially drive place cell remapping.
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