Sargolini, Francesca, Marianne Fyhn, Torkel Hafting, Bruce L. McNaughton, Menno P. Witter, May-Britt Moser, and Edvard I. Moser. “Conjunctive representation of position, direction, and velocity in entorhinal cortex.” Science 312, no. 5774 (2006): 758-762.

Abstract
Grid cells in the medial entorhinal cortex (MEC) are part of an environment-independent spatial coordinate system. To determine how information about location, direction, and distance is integrated in the grid-cell network, we recorded from each principal cell layer of MEC in rats that explored two-dimensional environments. Whereas layer II was predominated by grid cells, grid cells colocalized with head-direction cells and conjunctive grid × head-direction cells in the deeper layers. All cell types were modulated by running speed. The conjunction of positional, directional, and translational information in a single MEC cell type may enable grid coordinates to be updated during self-motion–based navigation.

Summary

The results suggest that, as the animal moves, the position vector may be updated through integration of position, direction, and speed signals in the grid cell network. Conjunctive cells are likely to play a critical role in this process. 

The conjunctive cells are located predominantly in layers III and V, where principal neurons have extensive axons projections to the grid  cell population in layer II. The ability of superficial cells to read out signals carried by these axons may be critical for translating activity over the population of grid cells, i.e., between cells with a different spatial phase, in a manner consistent with the rat’s motion.

The direction of translation may be determined by the head-direction input; the distance may be controlled by the speed modulation. In essence, this mechanism would perform path integration in the MEC network.

The integration of directional and positional information is strongly facilitated by the intermingled localization of the grid cells and the head-direction cells and the distributed representation of spatial phase and head orientation in these cell types. 

It remains to be determined whether the integration of position, direction, and velocity is confined to the local circuitry, as in the columns of the isocortex, or extends across the entire entorhinal sheet of grid cells, spanning all grid spacings.

For further info, please read the paper Sargolini et al. 2006.

Sargolini, Francesca, Marianne Fyhn, Torkel Hafting, Bruce L. McNaughton, Menno P. Witter, May-Britt Moser, and Edvard I. Moser. “Conjunctive representation of position, direction, and velocity in entorhinal cortex.” Science 312, no. 5774 (2006): 758-762.