Journal
BRAIN BEHAVIOR AND EVOLUTION
Volume 81, Issue 4, Pages 209-218Publisher
KARGER
DOI: 10.1159/000350709
Keywords
Allometry; Auditory cortex; Brain size; Evolution; Inferior colliculus; Medial geniculate nucleus
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Funding
- G. Harold and Leila Y. Mathers Charitable Foundation
- CNPq
- Faperj
- James S. McDonnell Foundation
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Allometric studies in primates have shown that the cerebral cortex, cerebellum, and remaining brain structures increase in size as a linear function of their numbers of neurons and non-neuronal cells across primates. Whether such scaling rules also apply to functionally related structures such as those of the auditory system is unknown. Here, we investigate the scaling of brain structures in the auditory pathway of six primate species and the closely related tree shrew. Using the isotropic fractionator method to estimate the numbers of neurons and non-neuronal cells in the inferior colliculus, medial geniculate nucleus, and auditory cortex (Ac), we assessed how they scaled across species and examined the relative scaling relationships among them. As expected, each auditory structure scales in mass as a linear function of its number of neurons, with no significant changes in neuronal density across species. The Ac scales proportionately with the cerebral cortex as a whole, maintaining a relative mass of approximately 1% and a relative number of neurons of 0.7%. However, the Ac gains neurons faster than both subcortical structures examined. As a result, larger primate brains have increased ratios of cortical to subcortical neurons involved in processing auditory information. Copyright (C) 2013 S. Karger AG, Basel
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