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Medial versus lateral modes for reconfiguring hippocampal representations

Joe Monaco

Mind/Brain Institute, The John Hopkins University, USA


Grid cells and other medial entorhinal cortex (MEC) cell types form the basis of the spatial inputs into hippocampus that drive the formation and remapping of hippocampal place representations. The grid-to-place transformation is at the crux of this processing stream that is critical to rodent spatial memory. However, the nature of lateral entorhinal cortex (LEC) activity, which is primarily non-spatial, and its interaction with hippocampus have not been fully characterized. The hypothesis of parallel lateral and medial streams of spatial and non-spatial information that are associated within hippocampus is broadly supported by anatomical and physiological data. We discuss implications of this idea for different types of remapping using two models. First, a rate-code competitive model of the grid-to-place transform demonstrates complete remapping between environments. Place units compete over simulated grid cell inputs to represent space using recurrent inhibition, allowing real-time readout of MEC realignment. Second, we use a phase-code feedback model to simulate double rotation experiments that put track cues and room cues in conflict. We show stable place activity by interference among a set of path-integrating theta oscillators with cues represented as fixed points in phase space. This allows varying degrees of cue manipulation and demonstrates a possible mode of LEC-MEC interaction for producing partial remapping and other responses observed in cue-conflict configurations. Simulation results are discussed in the context of new entorhinal recording data from circle track and open field experiments showing less theta modulation of activity in LEC than in MEC.