The Preferred Directions of Conjunctive Grid X Head Direction Cells in the Medial Entorhinal Cortex Are Periodically Organized

The discovery of speed-modulated grid, head direction, and conjunctive grid x head direc-tion cells in the medial entorhinal cortex has led to the hypothesis that path integration, theupdating of one’s spatial representation based on movement, may be carried out within thisregion. This hypothesis has been formalized by many computational models, including aclass known as attractor network models. While many of these models propose specificmechanisms by which path integration might occur, predictions of these specific mechanisms have not been tested. Here I derive and test a key prediction of one attractor networkpath integration mechanism. Specifically, I first demonstrate that this mechanism predicts aperiodic distribution of conjunctive cell preferred directions in order to minimize drift. Next, Itest whether conjunctive cell preferred directions are in fact periodically organized. Resultsindicate that conjunctive cells are preferentially tuned to increments of 36°, consistent withdrift minimization in this path integration mechanism. By contrast, no periodicity wasobserved in the preferred directions of either pure grid or pure head direction cells. Theseresults provide the first neural evidence of a nonuniform structure in the directional preferences of any head direction representation found in the brain.