Gray Level Index and Lateralization of Broca’s Area in Chimpanzees in Relation to Vocal Control

The evolution of language is a long-standing question in the field of biological anthropology. Broca’s area is a brain region in the inferior frontal gyrus consisting of Brodmann areas (BA) 44 and 45, which has a central role in language production. Past studies in humans have found significant left hemisphere lateralization of some aspects of microstructure in Broca’s area. This study aimed to understand if one of our closest living relatives, the chimpanzees, have similar population-level Broca’s area lateralization to provide further phylogenetic context to understand the neural basis of human language acquisition. To answer this question, we examined the right and left hemisphere gray matter in BA 44 and 45 of 19 post-mortem chimpanzee brains. During their lifetime, these chimpanzees were tested for their ability to produce novel vocalizations to capture the attention of an observer that was not oriented towards them. Analyzing these data on attention-getting vocalizations (AG), along with measures of cell profile density across the vertical layers of the cortex, we found no evidence for hemispheric lateralization across all individuals or in association with the AG+ phenotype. However, we found that AG+ individuals have significantly lower cell profile density overall across both hemispheres and subregions of Broca’s area, indicating relatively more space for neuropil, a proxy for brain connectivity. These results highlight the novelty of human-like levels of hemispheric lateralization for language dominance in evolutionary history.

Author

• Sherwood, Alison

Language

• en

Date created

• 2025

Type of Work

• Master's Thesis

License

• All rights reserved

Rights statement

• In Copyright

GW Unit

• Anthropology

Degree

• M.S.

Advisor

• Sherwood, Chet C

Persistent URL

•  https://scholarspace.library.gwu.edu/etd/xw42n890h