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The lecture will be delivered in English.

Neocortical neurons with similar functional properties assemble into spatially coherent circuits, but it remains unclear how inhibitory interneurons are organized in the cerebral neocortex. Recent in vitro studies suggested that the clusters of inhibitory interneurons originated from the same progenitor cells are clustered in the spatial domain of the developing neocortex. However, it is still not clear how long such a clustered distribution persists during postnatal development, and even if it persists to the adulthood, it remains unknown what is the functional significance of spatial clustering of GABAergic interneurons in operation of cortical circuits.

To address these questions, we applied in vivo two-photon functional Ca2+ imaging and whole-cell recording of synaptic currents to record visual responses of cortical neurons, and analyzed their spatial arrangements. GABAergic interneurons were clustered in the three-dimensional space of the adult visual cortex, and the three subtypes of interneurons, parvalbumin-, calretinin- and somatostatin-positive neurons also formed clusters with slightly overlapping each other. Excitatory neurons located within the clusters (insiders) had a lower amplitude and sharper orientation tuning of visual responses than outsiders, whereas the neurons near and far from non-clustered interneurons did not show the location-tuning/amplitude relationship. Furthermore, inhibitory synaptic currents recorded from the insiders were larger than those of the outsiders. These findings suggest that GABAergic interneurons form spatial clusters to make their inhibitory function more effective than isolated interneurons.

In this talk, I would like to discuss the functional significance of the spatial clustering of GABAergic neurons in the cortical circuit.