Exploring an innovative method for the automatic recognition of cortical sulci in cranial endocasts

Abstract

Knowledge of human brain evolution primarily relies on the interpretation of palaeoneurological evidence. In the absence of any direct evidence of the fossil neural condition, an endocast (i.e., replica of the internal table of the bony brain case) would constitute a proxy for reconstructing a timeline and mode of cerebral changes in human evolution. The identification of cerebral imprints, and more particularly, of cortical sulci, is indeed critical for assessing the topographic extension and structural organisation of cortical areas. As demonstrated by historical debates in palaeoneurology, however, the description of these crucial landmarks in fossil endocasts is challenging. The recent introduction of high-resolution imaging techniques in (palaeo)neurology offers new opportunities for tracking detailed endocranial neural characteristics. In such context, this study aimed to provide an atlas documenting the variation in the extant human, common chimpanzee and bonobo endocranial sulcal patterns for subsequent use as a comparative platform for the study of the fossil record. The total brain sample population for this study consisted of 60 formalin-fixed human brains from the Department of Anatomy, University of Pretoria, South Africa. Additionally, 58 extant human dry crania from the Pretoria Bone Collection (University of Pretoria, South Africa) which were detailed previously by X-ray microtomography (micro-CT) at the MIXRAD facility, located at the South African Nuclear Corporation (Necsa), Pelindaba, and 22 common chimpanzee and bonobo crania from the Royal Museum for Central Africa (Tervuren, Belgium) that had also been detailed previously using micro-CT at the Centre for X-ray Tomography of the Ghent University (UGCT) were processed and evaluated for inclusion in the study population. Sulci on formalin-fixed brains were documented to create a database of sulcal patterns representing a South African brain sample population. The endocasts were analysed using various software programs and appropriate algorithms, during the post-acquisition process. Finally, a probability map was constructed to document the variation of sulcal imprints on extant human endocasts, based on the identified sulci. This semi-automatic method provides an innovative, non-invasive, observer-independent method to investigate human endocranial structural organisation and a promising perspective for discussing long-standing questions in palaeoneurology.