Encoding of large discrete worlds in the temporal lobe and prefrontal cortex

In the medial entorhinal cortex (mEC), the interface between the hippocampus and the neocortex, grid cells fire at regular periodic intervals throughout an environment (Hafting et al., 2005). This phenomenon of firing at regular periodic distances could be used to perform useful calculations about the environment, such as path integration (McNaughton et al., 2006). Grid cell firing locations are at 60° from one another resulting in a hexagonal lattice of activity across the environment. Recently, hexagonal-like firing patterns in the entorhinal cortex have also been observed in non-spatial tasks (Constantinescu et al., 2016), opening up the possibility that the hexagonal grid code performs a more fundamental function that contributes to many other cognitive tasks in addition to spatial navigation. To investigate how we encode non-spatial dimensions, we are using large discrete worlds made up of 100s of stimuli connected together. We wish to understand how the temporal lobe and prefrontal cortex encodes the statistics of these discrete worlds. Does the brain employ place-like and grid-like coding just like in normal space? Or does it have an entirely different coding scheme for non-spatial statistical worlds.