Sulci 3D mapping from human cranial endocasts: A powerful tool to study hominin brain evolution

Abstract

Key questions in paleoneurology concern the timing and emergence of derived cerebral features within the human lineage. Endocasts are replicas of the internal table of the bony braincase that are widely used in paleoneurology as a proxy for reconstructing a timeline for hominin brain evolution in the fossil record. The accurate identification of cerebral sulci imprints in endocasts is critical for assessing the topographic extension and structural organisation of cortical regions in fossil hominins. High-resolution imaging techniques combined with established methods based on population-specific brain atlases offer new opportunities for tracking detailed endocranial characteristics. This study provides the first documentation of sulcal pattern imprints from the superolateral surface of the cerebrum using a population-based atlas technique on extant human endocasts. Human crania from the Pretoria Bone Collection (South Africa) were scanned using micro-CT. Endocasts were virtually extracted, and sulci were automatically detected and manually labelled.A density map method was applied to project all the labels onto an averaged endocast to visualise the mean distribution of each identified sulcal imprint. This method allowed for the visualisation of inter-individual variation of sulcal imprints, for example, frontal lobe sulci, correlating with previous brain-MRI studies and for the first time the extensive overlapping of imprints in historically debated areas of the endocast (e.g. occipital lobe). In providing an innovative, non-invasive, observerindependent method to investigate human endocranial structural organisation, our analytical protocol introduces a promising perspective for future research in paleoneurology and for discussing critical hypotheses on the evolution of cognitive abilities among hominins.

What do brain endocasts tell us? A comparative analysis of the accuracy of sulcal identification by experts and perspectives in palaeoanthropology

“…The aim of this study is, thus, to measure the accuracy of sulcal identification through an experiment that closely reproduces the conditions that palaeoneurologists face when working with hominin endocasts. The approach here is different from previous works (de Jager et al., 2022 ; Dumoncel et al., 2021 ), but complementary. By combining classic palaeoneurological approaches with new techniques available in the neuroimaging field, our work aims at answering the following questions: Is it possible to obtain an endocast or a similar proxy that reproduces external details of the human/hominid brain from an MRI scan?…”

“…Falk et al, 2018) is substantial. The same has been described for endocasts (de Jager et al, 2019(de Jager et al, , 2022. Therefore, trying to reconstruct a sulcus following the very general known shape/position in the literature or from a mean specimen may induce a bias when looking at an endocast and trying to follow the marks observed there.…”

“…The aim of this study is, thus, to measure the accuracy of sulcal identification through an experiment that closely reproduces the conditions that palaeoneurologists face when working with hominin endocasts. The approach here is different from previous works (de Jager et al, 2022;Dumoncel et al, 2021), but complementary.…”

Lateralized behaviors in living humans: Application in the context of hominin brain evolution

“…Moreover, an objective characterization of the relative position of the brain sulci and the resulting imprints of the bone has to be obtained through a unique methodological framework to improve the quality of the results, following previous studies (de Jager et al, , 2022.…”

First evidence of the link between internal and external structure of the human inner ear otolith system using 3D morphometric modeling

“…Knowledge of the relationship of bone to underlying soft tissues has been an important part of historical attempts to uncover structural, and by extension, functional relations in regions of the vertebrate skull. From Leonardo’s attempts to uncover the seat of the soul in the senso commune by using measurements to understand location (for reviews see 21 , 22 ) to uncovering the interface between the brain and skull 23 , researchers today continue to push the boundaries of how to visualize the relationships between internal vs. the external 24 – 26 . Most recently, and directly related to the PVS, are the significant advances in understanding the morphological interface of the bony SCCs and their internal duct system.…”