Variability of Broca's area homologue in African great apes: Implications for language evolution

Authors

  • Chet C. Sherwood,

    Corresponding author
    1. Department of Anthropology, Columbia University, New York, New York
    2. Fishberg Research Center for Neurobiology and Kastor Neurobiology of Aging Laboratories, Mount Sinai School of Medicine, New York, New York
    3. New York Consortium in Evolutionary Primatology, New York, New York
    • Department of Anthropology, Columbia University, 452 Schermerhorn Ext., 1200 Amsterdam Ave., New York, NY 10027
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    • Fax: (212) 854-7347

  • Douglas C. Broadfield,

    1. Department of Anthropology, Florida Atlantic University, Boca Raton, Florida
    2. Department of Biomedical Sciences, Florida Atlantic University, Boca Raton, Florida
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  • Ralph L. Holloway,

    1. Department of Anthropology, Columbia University, New York, New York
    2. New York Consortium in Evolutionary Primatology, New York, New York
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  • Patrick J. Gannon,

    1. New York Consortium in Evolutionary Primatology, New York, New York
    2. Department of Otolaryngology, Mount Sinai School of Medicine, New York, New York
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  • Patrick R. Hof

    1. Fishberg Research Center for Neurobiology and Kastor Neurobiology of Aging Laboratories, Mount Sinai School of Medicine, New York, New York
    2. New York Consortium in Evolutionary Primatology, New York, New York
    3. Departments of Geriatrics and Adult Development, Mount Sinai School of Medicine, New York, New YorkDepartment of Ophthalmology, Mount Sinai School of Medicine, New York, New York
    4. Foundation for Comparative and Conservation Biology, Rockville, Maryland
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Abstract

The cortical circuits subserving neural processing of human language are localized to the inferior frontal operculum and the posterior perisylvian region. Functional language dominance has been related to anatomical asymmetry of Broca's area and the planum temporale. The evolutionary history of these asymmetric patterns, however, remains obscure. Although testing of hypotheses about the evolution of language areas requires comparison to homologous regions in the brains of our closest living relatives, the great apes, to date little is known about normal interindividual variation of these regions in this group. Here we focus on Brodmann's area 44 in African great apes (Pan troglodytes and Gorilla gorilla). This area corresponds to the pars opercularis of the inferior frontal gyrus (IFG), and has been shown to exhibit both gross and cytoarchitectural asymmetries in humans. We calculated frequencies of sulcal variations and mapped the distribution of cytoarchitectural area 44 to determine whether its boundaries occurred at consistent macrostructural landmarks. A considerable amount of variation was found in the distribution of the inferior frontal sulci among great ape brains. The inferior precentral sulcus in particular was often bifurcated, which made it impossible to determine the posterior boundary of the pars opercularis. In addition, the distribution of Brodmann's area 44 showed very little correspondence to surface anatomy. We conclude that gross morphologic patterns do not offer substantive landmarks for the measurement of Brodmann's area 44 in great apes. Whether or not Broca's area homologue of great apes exhibits humanlike asymmetry can only be resolved through further analyses of microstructural components. Anat Rec Part A 271A:276–285, 2003. © 2003 Wiley-Liss, Inc.

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