the CA3 region has the ability to read and register the rich combinatorial output of the entorhinal cortex grid modules. The multiplicity of representations may be generated by independent changes of grid maps in the medial entorhinal cortex, but the orthogonalization may also benefit from intrinsic architectural properties of the hippocampus. The latter may be accomplished in two steps. First, the entorhinal cortex–mediated pattern is separated into subpatterns by the distinctive and low-divergence connectivity of granule cells to CA3 targets37,38. Second, the CA3 region can compute the distance relations among the discretized subpatterns and represent those relationships by the synaptic weights between the CA3 place cells and CA3-CA1 projections39. Taken together, the combined entorhinal cortex and hippocampal mechanisms may enable the storage of very large numbers of arbitrary associations without interfering with one another.
