How could the spatial maps of the medial entorhinal cortex sub-serve memory formation? The organization of the grid-cell network provides some clues. Grid cells are arranged as semi-independent modules or clusters along the dorsal-to-ventral axis of the medial entorhinal cortex, with small grid scales dominating in dorsal parts and large grid scales being more abundant in ventral parts. Steps in grid scale go hand in hand with quantal shifts of orientation and asymmetry in the grid pattern32. Different modules may respond independently to changes in the geometry of the environment. The functional autonomy of the grid modules has important consequences for representation of space in downstream hippocampal cell populations (Fig. 3a). Their ability to respond differentially to reconfiguration of the environment supplies a rich combination of efferent patterns to the hippocampus33, which may be sufficient to generate large numbers of discrete maps individualized to the vast number of environments the animal visits in its lifetime.
