Welcome!
At the Laboratory of Comparative Neuroanatomy we use quantitative morphological approaches to investigate the diversity of the nervous system across animals, its evolution and developmental origins.
Most of our studies apply the Isotropic Fractionator, a non-stereological method developed in the lab that allows the fast, simple and reliable determination of numbers of neuronal and non-neuronal cells in any dissectable brain structure.
To assess the scaling rules that underlie diversity and its evolution, we compare the cellular composition of brain structures across adult individuals of various species (27 and counting) across several orders (primates, rodents and insectivores, so far).
To investigate the developmental origins of diversity, we compare the cellular composition of the brain of given species across multiple pre- and post-natal developmental timepoints.
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Just published
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Why does the human brain cost 20% of the body energy budget, if it only represents 2% of body mass? Simply because of its very large number of neurons. Here it is shown that brain metabolism scales linearly across species with the number of brain neurons.
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Not 100 billion neurons, not 10 x more glia: Herculano-Houzel reviews in Frontiers in Human Neuroscience the evidence on the numbers of neuronal and non-neuronal cells that compose the human brain and how that makes it a linearly scaled-up primate brain.
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Great ape brains are linearly scaled-up primate brains: implications for hominin evolution, BBE 2011Why is the human brain relatively large compared to a gorilla brain? "Because great apes have evolved a large body size", is our proposition in this paper that also estimates the number of neurons in the brains of extinct hominins
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The primate cerebral cortex expands with a larger number of neurons of which a decreasing fraction is connected through the white matter, in a manner that we propose to drive the folding of the grey matter.
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Main findings
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Comparative analyses of brain size so far have lumped different taxa together, assuming that they followed the same scaling rules. By comparing rodents, primates and insectivores, we showed that each order follows its own scaling rules.
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From mice to capybaras, average neuronal size becomes larger as numbers of neurons in the cerebral cortex, cerebellum and remaining areas increase (Herculano-Houzel et al., PNAS 2006).
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Compared to rodents, this is a much more economical way to build a brain: Since average neuronal size does not increase with larger number of neurons, primate brains hold more neurons than rodent brains of the same size (Herculano-Houzel et al PNAS 2007).
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Contrary to the usual notion, we have found that, across primate species, this number can vary by about 3x, depending on variations in neuronal density that are not correlated with brain size (Herculano-Houzel et al., PNAS 2008).
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With about 1.5 kg and holding 86 billion neurons and 85 non-neuronal cells, we have found that the adult human brain conforms to the linear scaling rules that apply to other primate species: We are not special, after all (Azevedo et al. J Comp Neur 2009).
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Absolute size increases coordinately across these structures, but relative cortical size increases while relative cerebellar size does not. This discrepancy can be eliminated by looking at numbers of neurons directly in primates, rodents and insectivores.
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Ongoing studies
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White matter volume scales faster than grey matter volume and number of neurons in a way that indicates that cortical connectivity through the WM decreases with increasing numbers of neurons in the GM. Presented at the SfN meeting in Chicago, 2009.
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