Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain

Authors

  • Frederico A.C. Azevedo,

    1. Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão 21941-590 Rio de Janeiro, Brazil
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  • Ludmila R.B. Carvalho,

    1. Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão 21941-590 Rio de Janeiro, Brazil
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  • Lea T. Grinberg,

    1. Grupo de Estudos em Envelhecimento Cerebral da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
    2. Instituto Israelita de Ensino e Pesquisa Albert Einstein
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  • José Marcelo Farfel,

    1. Grupo de Estudos em Envelhecimento Cerebral da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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  • Renata E.L. Ferretti,

    1. Grupo de Estudos em Envelhecimento Cerebral da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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  • Renata E.P. Leite,

    1. Grupo de Estudos em Envelhecimento Cerebral da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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  • Wilson Jacob Filho,

    1. Grupo de Estudos em Envelhecimento Cerebral da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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  • Roberto Lent,

    1. Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão 21941-590 Rio de Janeiro, Brazil
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    • The last two authors contributed equally to this work.

  • Suzana Herculano-Houzel

    Corresponding author
    1. Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão 21941-590 Rio de Janeiro, Brazil
    • Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Av. Brigadeiro Trompowski s/n, Ilha do Fundão 21941-590 Rio de Janeiro-RJ, Brasil
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    • The last two authors contributed equally to this work.


Abstract

The human brain is often considered to be the most cognitively capable among mammalian brains and to be much larger than expected for a mammal of our body size. Although the number of neurons is generally assumed to be a determinant of computational power, and despite the widespread quotes that the human brain contains 100 billion neurons and ten times more glial cells, the absolute number of neurons and glial cells in the human brain remains unknown. Here we determine these numbers by using the isotropic fractionator and compare them with the expected values for a human-sized primate. We find that the adult male human brain contains on average 86.1 ± 8.1 billion NeuN-positive cells (“neurons”) and 84.6 ± 9.8 billion NeuN-negative (“nonneuronal”) cells. With only 19% of all neurons located in the cerebral cortex, greater cortical size (representing 82% of total brain mass) in humans compared with other primates does not reflect an increased relative number of cortical neurons. The ratios between glial cells and neurons in the human brain structures are similar to those found in other primates, and their numbers of cells match those expected for a primate of human proportions. These findings challenge the common view that humans stand out from other primates in their brain composition and indicate that, with regard to numbers of neuronal and nonneuronal cells, the human brain is an isometrically scaled-up primate brain. J. Comp. Neurol. 513:532–541, 2009. © 2009 Wiley-Liss, Inc.

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