What makes us human, at the neuronal network level? We discovered a dramatic (10-fold) expansion of interneuron-to-interneuron networks in the human brain compared to mouse: just published in @ScienceMagazine @MpiBrain @maxplanckpress https://t.co/eRYZyDyKVz pic.twitter.com/BmpwkF5922— Moritz Helmstaedter 🇺🇦 (@mh_lab) June 24, 2022
Abstract: The human cerebral cortex houses 1,000 times more neurons than the cerebral cortex of a mouse, but the possible differences in synaptic circuits between these species are still poorly understood. We used 3-dimensional electron microscopy of mouse, macaque and human cortical samples to study their cell type composition and synaptic circuit architecture. The 2.5-fold increase in interneurons in humans compared to mouse was compensated by a change in axonal connection probabilities and therefore did not yield a commensurate increase in inhibitory-vs-excitatory synaptic input balance on human pyramidal cells. Rather, increased inhibition created an expanded interneuron-to-interneuron network, driven by an expansion of interneuron-targeting interneuron types and an increase in their synaptic selectivity for interneuron innervation. These constitute key neuronal network alterations in human cortex.