Cortical folding scales universally with surface area and thickness, not number of neurons
The best way to fold a mammalian brain
As mammalian brains grew larger through evolution, the organization and folding of brains changed too. In a series of statistical analyses comparing a large number of mammalian species, Mota and Herculano-Houzel found that brain folding is not simply a phylogenetic consequence of brain mass increase (see the Perspective by Striedter and Srinivasan). The exposed surface of the cortex scales across all mammals and across individuals as a single power law of the product of total cortical surface and the square root of cortical thickness.
Abstract
Larger brains tend to have more folded cortices, but what makes the cortex fold has remained unknown. We show that the degree of cortical folding scales uniformly across lissencephalic and gyrencephalic species, across individuals, and within individual cortices as a function of the product of cortical surface area and the square root of cortical thickness. This relation is derived from the minimization of the effective free energy associated with cortical shape according to a simple physical model, based on known mechanisms of axonal elongation. This model also explains the scaling of the folding index of crumpled paper balls. We discuss the implications of this finding for the evolutionary and developmental origin of folding, including the newfound continuum between lissencephaly and gyrencephaly, and for pathologies such as human lissencephaly.
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References and Notes
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Published In
Science
Volume 349 | Issue 6243
3 July 2015
3 July 2015
Copyright
Copyright © 2015, American Association for the Advancement of Science.
Submission history
Received: 13 February 2015
Accepted: 11 May 2015
Published in print: 3 July 2015
Acknowledgments
Supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, INCT/MCT, and the James S. McDonnell Foundation. Data reported in the paper are presented in the supplementary materials.
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- Bruno Mota,
- Suzana Herculano-Houzel
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