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If you have a question about this talk, please contact Fiona Woods.


Extracellular recordings have provided detailed phenomenology of the spatial discharge patterns of place cells, grid cells, and head direction cells in the rodent brain. However, very little is known about the underlying microcircuits. We devised methods that allow the identification of neurons in freely moving animals, using the patchy architecture of layer 2 in medial entorhinal cortex as a reference. Calbindin-positive pyramidal neurons in layer 2 of medial entorhinal cortex are arranged in a regular and often hexagonal grid. Across animals this grid of patches shows a consistent alignment to the parasubiculum; cholinergic inputs and layer 1 axons also run along a grid axis. I will provide evidence that grid cells correspond largely to these calbindin-positive pyramidal neurons and conclude that layer 2 grid discharges originate in a spatiotemporally highly organized microcircuit, a pyramidal ‘grid cell grid’.