The Hippocampus Converts Volatile Entorhinal Inputs into Stable Spatial Maps

Abstract

The medial entorhinal cortex (MEC)-hippocampal network plays a key role in the processing, storage and recall of spatial information. However, how the spatial code provided by MEC inputs relates to spatial representations generated by principal cell assemblies within hippocampal subfields remains enigmatic. To investigate this coding relationship, we employed two-photon calcium imaging in mice navigating through dissimilar virtual environments. Imaging large MEC bouton populations revealed spatially tuned activity patterns. MEC inputs drastically changed their preferred spatial field locations between environments, whereas hippocampal cells showed lower levels of place field reconfiguration. Decoding analysis indicated that higher place field reliability and larger context-dependent activity-rate differences allow low numbers of principal cells, particularly in the DG and CA1, to provide a more rapid and accurate information about location and context than MEC inputs. Thus, conversion of volatile MEC inputs into stable spatial hippocampal maps may enable fast encoding and efficient recall of spatio-contextual information.