In addition, we recently found that the size of dendritic arbors strongly modulates the shape of the action potential onset at the axon initial segment it is accelerated in neurons with larger dendritic surface area ( Eyal et al. Dendritic geometry strongly affects the action potential firing pattern of neurons ( Mainen and Sejnowski 1996). Mammalian dendrites have a rich repertoire of electrical and chemical dynamics, and individual neurons are capable of sophisticated information processing ( Yuste and Tank 1996). From many experimental and computational studies investigating neurons in brains of laboratory animals, we now know that a strong interdependence exists between dendritic and axonal morphology and information processing capabilities of a neuron ( Mainen and Sejnowski 1996 Yuste and Tank 1996 Segev and Rall 1998 Magee 2000 van Elburg and van Ooyen 2010 Eyal et al. The cellular organization of the human brain has been the focus of neuroscience research ever since Ramon y Cajal and Golgi's groundbreaking work of more than a century ago. We thus provide a quantitative analysis of “full” human neuron morphologies and present direct evidence that human neurons are not “scaled-up” versions of rodent or macaque neurons, but have unique structural and functional properties. Computational modeling of passive electrical properties to assess the functional impact of large dendrites indicates stronger signal attenuation of electrical inputs compared with mouse. Unsupervised cluster analysis classified 88% of human L2 and 元 neurons into human-specific clusters distinct from mouse and macaque neurons. Next, we show that human L(ayer) 2 and 元 pyramidal neurons have 3-fold larger dendritic length and increased branch complexity with longer segments compared with temporal cortex neurons from macaque and mouse. Importantly, morphologies did not correlate to etiology, disease severity, or disease duration. Here, we obtained human brain tissue during resection surgery and reconstructed basal and apical dendrites and axons of individual neurons across all cortical layers in temporal cortex (Brodmann area 21). Whether it translates to human is not known since quantitative data on “full” human neuronal morphologies are lacking. Our knowledge on neuronal structure and function is primarily based on brains of laboratory animals. The size and shape of dendrites and axons are strong determinants of neuronal information processing.
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