The human cerebral cortex houses 1000 times more neurons than that of the cerebral cortex
of a mouse, but the possible differences in synaptic circuits between these species are still
poorly understood. We used three-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 with mice was
compensated by a change in axonal connection probabilities and therefore did not yield a …