Cited by 579Neurogenesis and neuroplasticity mechanismsPrimate Behavior and EcologyEvolution and Paleontology Studies

: Cellular scaling rules for rodent brains.

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Herculano-Houzel, Suzana, Mota, Bruno, Lent, Roberto·2006·Proceedings of the National Academy of Sciences

Abstract

How do cell number and size determine brain size? Here, we show that, in the order Rodentia, increased size of the cerebral cortex, cerebellum, and remaining areas across six species is achieved through greater numbers of neurons of larger size, and much greater numbers of nonneuronal cells of roughly invariant size, such that the ratio between total neuronal and nonneuronal mass remains constant across species. Although relative cerebellar size remains stable among rodents, the number of cerebellar neurons increases with brain size more rapidly than in the cortex, such that the cerebellar fraction of total brain neurons increases with brain size. In contrast, although the relative cortical size increases with total brain size, the cortical fraction of total brain neurons remains constant. We propose that the faster increase in average neuronal size in the cerebral cortex than in the cerebellum as these structures gain neurons and the rapidly increasing glial numbers that generate glial mass to match total neuronal mass at a fixed glia/neuron total mass ratio are fundamental cellular constraints that lead to the relative expansion of cerebral cortical volume across species.

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Crossref · 10.1073/pnas.0604911103

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  • The cerebral cortex varies in relative size from 42% in the mouse to 82% in the human, but contains between 13 and 28% of all brain neurons in 15 of 18 species studied, ranging from 13% in moles to 41% in the squirrel monkey.

    “the cerebral cortex, despite varying in relative size from 42% (in the mouse) to 82% of brain mass (in the human), contains between 13 and 28% of all brain neurons in 15 of 18 species studied, ranging between 13% (in moles) and 41% (in the squirrel monkey; Herculano-Houzel et al., 2006, 2007; Sarko et al., 2009).”

    From The human brain in numbers: a linearly scaled-up primate brain (2009) · cites this paper as Herculano-Houzel et al., 2006

    The Results (page not provided) report that cortical mass increases with brain size while the cortex contains a relatively stable 17.8 ± 3.4% of brain neurons across six rodent species. This supports the general pattern, but the paper does not establish the quoted 42%–82% mass range or the neuron percentages across 18 species, including humans, moles, and squirrel monkeys. (LLM, conf=0.88)

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  • In mammals, the pallium accounts for most of total brain volume, but the cerebellum houses a large majority of brain neurons.

    “This markedly contrasts with the situation found in mammals, in which the pallium accounts for most of total brain volume, but the cerebellum houses a large majority of brain neurons (32–39)”

    From Birds have primate-like numbers of neurons in the forebrain (2016) · cites this paper as [32]

    The Results report that the cerebellum contains 59.0%–72.4% of brain neurons in the six rodent species studied, while the cerebral cortex becomes the dominant structure by volume as brain size increases. The source does not establish that the pallium occupies most brain volume across mammals generally, or even across all six rodents. The indexed passages have section labels but no page numbers. (LLM, conf=0.86)

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  • Like in mammals, the proportion of nonneuronal cells is very small in the cerebellum, varying between 12% and 19% in songbirds and between 14% and 19% in parrots, but, in contrast to mammals, nonneuronal cells also constitute a minor cellular fraction in the telencephalon, representing 21-40% of cells in songbirds and 31-43% of cells in parrots.

    “Like in mammals (32–39, 46), the proportion of nonneuronal cells is very small in the cerebellum, varying between 12% and 19% in songbirds and between 14% and 19% in parrots, but, in contrast to mammals, nonneuronal cells also constitute a minor cellular fraction in the telencephalon, representing 21–40% of cells in songbirds and 31–43% of cells in parrots”

    From Birds have primate-like numbers of neurons in the forebrain (2016) · cites this paper as [32]

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  • In Rodentia, brain size increases faster than neuron number, with neuronal density decreasing; with constant non-neuronal density, this implies average neuronal size increases rapidly as neurons become more numerous.

    “In the order Rodentia, we find that the brain increases in size faster than it gains neurons, with a decrease in neuronal densities which, in the presence of constant non-neuronal cell densities, implies that average neuronal size increases rapidly as neurons become more numerous (Herculano-Houzel et al., 2006).”

    From The human brain in numbers: a linearly scaled-up primate brain (2009) · cites this paper as Herculano-Houzel et al., 2006

  • The HiAER-Spike system capacity is roughly twice the neurons of a mouse brain and runs at faster than real time.

    “In this work, we present HiAER-Spike, a modular, recon fi gurable, event-driven neuromorphic computing platform designed to execute large spiking neural networks with up to 160 million neurons and 40 billion synapses - roughly twice the neurons of a mouse brain at faster than real time.”

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Research works printed but not linked: 1

  1. [9]Frahm H. D., Stephan H., Stephan M. J. Hirnforsch. 1982;23:375–389. [PubMed] [Google Scholar]

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Authors
Herculano-Houzel, S., Mota, B., & Lent, R.
Affiliations
  • *Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, Brazil; and
  • Centro Brasileiro de Pesquisas Físicas (BR)
  • Universidade Federal do Rio de Janeiro (BR)
Venue
Proceedings of the National Academy of Sciences
Published
2006-08-08
Volume
103
Issue
32
Pages
12138-12143
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
OpenAlex
W2166670234
Cited by
579
References
43
Citations by year
2026: 27 · 2025: 29 · 2024: 58 · 2023: 51 · 2022: 36 · 2021: 51 · 2020: 64 · 2019: 26 · 2018: 31 · 2017: 22 · 2016: 29 · 2015: 19 · 2014: 28 · 2013: 21 · 2012: 18
FWCI
3.67
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico
  • Universidade Federal do Rio de Janeiro
Topics
  • Life Sciences › Neuroscience › Developmental Neuroscience › Neurogenesis and neuroplasticity mechanisms
  • Social Sciences › Psychology › Social Psychology › Primate Behavior and Ecology
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
Keywords
brain scaling, rodent brain, cerebral cortex, cerebellum, neuron size, non-neuronal cells, brain size evolution, cross-species comparison, cortical expansion
MeSH terms
Animals, Brain, Cerebellum, Cerebral Cortex, Guinea Pigs, Male, Models, Neurological, Neurons, Rodentia, Species Specificity, Rats, Wistar, Mice, Rats

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