Of mice and men: topologically complex dendrites assemble uniquely human networks

The organizational principles that distinguish the human brain from other species have been a long-standing enigma in neuroscience. Focusing on the uniquely evolved cortical layers 2 and 3 in human, human pyramidal neurons show more intense connectivity among themselves compared to the mouse. This is surprising because human L2 and 3 neurons are much sparser. We show that the number and size of neurons per se fail to account for this connectivity difference, suggesting that another property of neurons is key in determinant of human network connectivity. Topological comparison of dendritic structure reveals much higher perisomatic (basal and oblique) branching density in human pyramidal cells. Using topological tools we quantitatively show that this cellular-level structural property directly impacts network-level topological complexity, including the formation of a rich subnetwork structure. We conclude that greater dendritic complexity, which is a defining attribute of human L2 and 3 neurons, may provide enhanced computational capacity and cognitive flexibility to the human cortex. ### Competing Interest Statement The authors have declared no competing interest.