The medial entorhinal spatial map is built on excitatory-inhibitory network motifs defined by their functional cell type and theta modulation

The medial entorhinal cortex (mEC) contains functionally specific neurons crucial for spatial memory and navigation, including grid, border, spatial, head direction, and cue cells. However, how these neurons interact to build spatial maps remains unclear. Here, using simultaneous recordings from hundreds of functionally defined mEC neurons in mice navigating virtual tracks with varying numbers of visual landmarks, we uncovered connectivity motifs that define the mEC functional network architecture and link it to the principles governing allocentric map formation. We found that connectivity between cells was cell-type-specific and grouped into subnetworks based on their function and theta modulation, with theta modulated connections dominating over non-theta. Functionally distinct neurons preferentially connected to their own type, and their interactions were coordinated by a shared inhibitory pool of interneurons, with a higher proportion of excitatory-to-inhibitory connections than between excitatory cells. This was accompanied by the number of fields formed across all mEC cell types increasing sublinearly with the number of available cues. Grid cells showed the strongest relative connectivity to interneurons regardless of their theta modulation, linking otherwise largely isolated theta and non-theta streams. Grid cells were also least likely to form a field in response to cues. Together, these findings reveal an mEC network architecture organised by cell type and theta dependency, in which inhibitory interactions, with grid cells as the strongest hub, play a central role in building the mEC allocentric map.