Abstract
The organizational principles that distinguish the human brain from those of other species have been a long-standing enigma in neuroscience. Here, we leverage advances in algebraic topology to uncover the structural properties of the human brain at subcellular resolution. First, we reveal a much higher perisomatic branching density in pyramidal neurons when comparing homologous cortical regions in humans and mice. Traditional scaling methods consistently fail to interpret this difference, suggesting a distinctive feature of human pyramidal neurons. We next show that topological complexity leads to highly interconnected pyramidal-to-pyramidal and higher-order networks, which is unexpected in view of reduced neuronal density in humans compared to mouse neocortex. We thus present robust evidence that reduced neuronal density but increased topological complexity in human neurons ultimately leads to highly interconnected cortical networks. The dendritic complexity, which is a defining attribute of human brain networks, may serve as the foundation of enhanced computational capacity and cognitive flexibility.
Graphical abstract A. Human neural networks are different from mice due to their lower neuron density, resulting in increased distances between neurons, particularly among pyramidal cells. B. The topological analysis of layer 2/3 pyramidal cells in the cortex reveals an intriguing difference: human neurons exhibit a significantly larger number of dendritic branches, especially near the cell body compared to mice. This phenomenon is termed ”higher topological complexity” in dendrites. C. The combination of reduced neuron density and enhanced dendritic complexity results in greater network complexity within the human brain. Network complexity is defined by larger groups of neurons forming complex interconnections throughout the network. Our findings suggest that dendritic complexity wields a more substantial influence on network complexity than neuron density does, hinting at a potential strategy for enhancing cognitive abilities.
Competing Interest Statement
The authors have declared no competing interest.
