Journal
CEREBRAL CORTEX
Volume 20, Issue 3, Pages 730-742Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/cercor/bhp138
Keywords
cytoarchitecture; evolution; great ape; handedness; stereology
Categories
Funding
- National Science Foundation [BCS-0515484, BCS-0549117, BCS-0824531, DGE-0801634]
- National Institutes of Health [NS 42867]
- James S. Mc Donnell Foundation [22002078]
- Division Of Behavioral and Cognitive Sci
- Direct For Social, Behav & Economic Scie [0827531] Funding Source: National Science Foundation
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Neural changes that occurred during human evolution to support language are poorly understood. As a basis of comparison to humans, we used design-based stereological methods to estimate volumes, total neuron numbers, and neuron densities in Brodmann's areas 44 and 45 in both cerebral hemispheres of 12 chimpanzees (Pan troglodytes), one of our species' closest living relatives. We found that the degree of interindividual variation in the topographic location and quantitative cytoarchitecture of areas 44 and 45 in chimpanzees was comparable to that seen in humans from previous studies. However, in contrast to the documented asymmetries in humans, we did not find significant population-level hemispheric asymmetry for any measures of areas 44 and 45 in chimpanzees. Furthermore, there was no relationship between asymmetries of stereological data and magnetic resonance imaging-based measures of inferior frontal gyrus morphology or hand preference on 2 different behavioral tasks. These findings suggest that Broca's area in the left hemisphere expanded in relative size during human evolution, possibly as an adaptation for our species' language abilities.
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