Wernicke's area homologue in chimpanzees IPan troglodytes and its relation to the appearance of modern human language

Muhammad A. Spocter, William D. Hopkins, Amy R. Garrison, Amy L. Bauernfeind, Cheryl D. Stimpson, Patrick R. Hof, Chet C. Sherwood

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

Human language is distinctive compared with the communication systems of other species. Yet, several questions concerning its emergence and evolution remain unresolved. As a means of evaluating the neuroanatomical changes relevant to language that accompanied divergence from the last common ancestor of chimpanzees, bonobos and humans, we defined the cytoarchitectonic boundaries of area Tpt, a component of Wernicke's area, in 12 common chimpanzee brains and used designbased stereologic methods to estimate regional volumes, total neuron number and neuron density. In addition, we created a probabilistic map of the location of area Tpt in a template chimpanzee brain coordinate space. Our results show that chimpanzees display significant population-level leftward asymmetry of area Tpt in terms of neuron number, with volume asymmetry approaching significance. Furthermore, asymmetry in the number of neurons in area Tpt was positively correlated with asymmetry of neuron numbers in Brodmann's area 45, a component of Broca's frontal language region. Our findings support the conclusion that leftward asymmetry of Wernicke's area originated prior to the appearance of modern human language and before our divergence from the last common ancestor. Moreover, this study provides the first evidence of covariance between asymmetry of anterior and posterior cortical regions that in humans are important to language and other higher order cognitive functions.

Original languageEnglish
Pages (from-to)2165-2174
Number of pages10
JournalProceedings of the Royal Society B: Biological Sciences
Volume277
Issue number1691
DOIs
StatePublished - Jul 22 2010

Keywords

  • Asymmetry
  • Chimpanzee
  • Cytoarchitecture
  • Evolution
  • Wernicke's area

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