Variability and Asymmetry of the Sulcal Contours Defining Broca’s Area Homologue in the Chimpanzee Brain Simon S. Keller, 1,2 * Michael Deppe, 2 Marc Herbin, 3 and Emmanuel Gilissen 4,5,6 1 The Department of Clinical Neuroscience, Institute of Psychiatry, King’s College London, UK 2 The Department of Neurology, University of Mu ¨nster, D-48129 Mu ¨nster, Germany 3 UMR 7179 USM301 MNHN-CNRS, Museum National d’Histoire Naturelle, 75231 Paris cedex 05, France 4 Royal Museum for Central Africa, 3080 Tervuren, Belgium 5 Laboratory of Histology and Neuropathology, Universite ´ Libre de Bruxelles, B-1050 Brussels, Belgium 6 Department of Anthropology, University of Arkansas, Fayetteville, Arkansas 72701 ABSTRACT There has been recent motivation to search for neuroana- tomical asymmetries in nonhuman primates in order to provide comparative information on how the human brain is structurally organized to support specific cognitive capabilities, such as language functions. We took the op- portunity to study Broca’s area homologue in a novel sample of 80 preserved postmortem chimpanzee (Pan troglodytes) cerebral hemispheres. Consistent with the only prior study documenting the morphology of Broca’s area homologue in the chimpanzee (Sherwood et al. [2003] Anat Rec 271:276–285), we report great interindi- vidual variation in the structure and connections of the sulci investigated, most notably a left-sided bias in the bifurcation of the inferior precentral sulcus, an anatomi- cal feature that occurs much more frequently in chimpan- zees relative to humans. Consistent with our recent neuroimaging report (Keller et al. [2009b] J Neurosci 29:14607–14616), no population-based interhemispheric asymmetries of sulcal length existed that could be con- sidered markers of the size of Broca’s area homologue. With strict anatomical guidelines, we report that the diag- onal sulcus was present in 25% left and 20% right chim- panzee hemispheres studied, which is substantially less that the general prevalence in humans. Through the pre- sentation of schematic drawings, photographs, morpho- logical recordings and sulcal length metrics, our data illustrate the interindividual variability of Broca’s area homologue in the chimpanzee and support the notion of no macroscopic asymmetry of this important homologous language brain region in one of the closest evolutionary ancestor to modern humans J. Comp. Neurol. 520:1165–1180, 2012. V C 2011 Wiley Periodicals, Inc. INDEXING TERMS: asymmetry; cerebral cortex; comparative; ex vivo; evolution; great apes; language; sulci It has long been suspected that neuroanatomical asymmetries, particularly of brain regions forming por- tions of cortical networks supporting language functions, may provide an architectural basis for the functional orga- nization of language in the human brain (Witelson and Kigar, 1988). Broca’s area is a critical part of a wider cort- ical network that has important functions for, but is not restricted to, the expression of speech. Given that the left cerebral hemisphere is dominant for language in the vast majority of the healthy human population (Knecht et al., 2000a,b) and that functional asymmetries are associated with Broca’s area itself (Cooper, 2006; Keller et al., 2009a; Ojemann, 1979), there has been a search for left- ward interhemispheric asymmetries of Broca’s area using neuroimaging approaches (Dorsaint-Pierre et al., 2006; Foundas et al., 1996; Josse et al., 2009; Keller et al., 2009a, 2011). Findings have been inconsistent, which may be due to the effect of different applications of neu- roimaging methodologies (Keller et al., 2009a). However, in the absence of language lateralization data in the same subjects, direct anatomical examinations of Broca’s area have been more consistent with reports of leftward Grant sponsor: ‘‘Paul Broca II’’ project, 6th Framework Program of the European Community; Grant number: 029023 (to S.S.K; E.G.); Grant sponsor: Collaborative Research Centre SFB/TR 3 (Project A8) of the Deutsche Forschungsgemeinschaft (DFG; to S.S.K., M.D.). *CORRESPONDENCE TO: Simon S. Keller, The Department of Clinical Neuroscience, Institute of Psychiatry, Box PO43, De Crespigny Park, King’s College London, SE5 8AF, UK. E-mail: simon.keller@kcl.ac.uk V C 2011 Wiley Periodicals, Inc. Received March 11, 2010; Revised October 1, 2010; Accepted July 26, 2011 DOI 10.1002/cne.22747 Published online 8 August 2011 in Wiley Online Library (wileyonlinelibrary. com) The Journal of Comparative Neurology | Research in Systems Neuroscience 520:1165–1180 (2012) 1165 RESEARCH ARTICLE