A medial entorhinal connectome reveals compartmentalized microcircuit architecture

A synapse-resolution connectome of mouse medial entorhinal cortex and adjacent parasubiculum reveals an exclusion core (ExC) that partitions basal dendrites and synaptic connectivity within an L2 pyramidal cluster.

• Why it matters: The MEC’s role in transforming multimodal inputs into spatial representations is known, but how synaptic wiring and geometry implement its computations across layers and regions is unclear.
• What they did: Using serial electron microscopy, the authors mapped connectivity across all six MEC layers and the parasubiculum, then exhaustively reconstructed one L2 pyramidal cluster and tested a spatially constrained dendritic growth model.
• The result: Within the ExC, pyramidal neurons form a compact recurrent excitatory network that converges on shared inhibitory partners, with basket cells and recurrent Martinotti cells providing perisomatic and apical feedback.

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