Recent experiments support the theoretical hypothesis that recurrent connectivity plays a central role within the medial entorhinal cortex, by shaping activity of large neural populations, such that their joint activity lies within a continuous attractor. This conjecture involves dynamics within each population (module) of cells that share the same grid spacing. In addition, recent theoretical works raise a hypothesis that, taken together, grid cells from all modules maintain a sophisticated representation of position with uniquely large dynamical range, when compared with other known neural codes in the brain. To maintain such a code, activity in different modules must be coupled, within the entorhinal cortex or through the hippocampus.
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I thank Dori Derdikman, Ila Fiete, Neta Ravid, Haim Sompolinsky, and Nachum Ulanovsky for many helpful comments on the manuscript, and Hannah Monyer for a helpful discussion. Support from the Gatsby Charitable Foundation is gratefully acknowledged.