Validation of plaster endocast morphology through 3D CT image analysis

Endocranial anatomy of the Guercy 1 early Neanderthal from Baume Moula-Guercy (Soyons, Ardèche, France)

We provide the first comparative description of the endocranium of the Guercy 1 Early Neanderthal and examine its affinities to Preneanderthals, Neanderthals, and Homo sapiens. The Guercy 1 cranium derives from deposits chronostratigraphically and biostratigraphically dated to the Eemian Interglacial (MIS 5e). For comparative purposes, we compiled a sample of European and Southwest Asian subadult and adult Middle-to-Late Pleistocene hominins (≈MIS 12-MIS 1; N = 65). We sampled both a Preneanderthal-Neanderthal group and a Homo sapiens group. The Preneanderthal-Neanderthal group was further divided into three time-successive subgroups defined by associated MIS stages. Metric and morphological observations were made on original fossils and physical and virtual endocranial reconstructions. Guercy 1 and other Early Neanderthals, differ from Preneanderthals by increased development of the prefrontal cortex, precentral and postcentral gyri, inferior parietal lobule, and frontoparietal operculum. Early Neanderthal differ, in general, from Late Neanderthals by exhibiting less development in most of the latter brain structures. The late group additionally differentiates itself from the early group by a greater development of the rostral superior parietal lobule, angular gyrus, superior and middle temporal gyri, and caudal branches of the superior temporal gyrus. Endocranial morphology assessed along the Preneanderthal-Neanderthal sequence show that brain structures prominent in Preneanderthals are accentuated in Early-to-Late Neanderthals. However, both the Early and Late groups differentiate themselves by also showing regionally specific changes in brain development. This pattern of morphological change is consistent with a mosaic pattern of neural evolution in these Middle-to-Late Pleistocene hominins.

Digital Endocasting in Comparative Canine Brain Morphology

Computed tomography (CT) is one of the most useful techniques for digitizing bone structures and making endocranial models from the neurocranium. The resulting digital endocasts reflect the morphology of the brain and the associated structures. Our first aim was to document the methodology behind creating detailed digital endocasts of canine skulls. We created digital endocasts of the skulls of 24 different dog breeds and 4 wild canids for visualization and teaching purposes. We used CT scanning with 0.323 mm × 0.322 mm × 0.6 mm resolution. The imaging data were segmented with 3D Slicer software and refined with Autodesk Meshmixer. Images were visualized in 3D Slicer and surface models were converted to 3D PDFs to provide easier interactive access, and 3D prints were also generated for visualization purposes. Our second aim was to analyze how skull length and width relate to the surface areas of the prepiriform rhinencephalic, prefrontal, and non-prefrontal cerebral convexity areas of the endocasts. The rhinencephalic area ratio decreased with a larger skull index. Our results open the possibility to analyze the relationship between the skull and brain morphology, and to link certain features to behavior, and cognition in dogs.

Human paleoneurology: Shaping cortical evolution in fossil hominids

Evolutionary neuroanatomy must integrate two different sources of information, namely from fossil and from living species. Fossils supply information concerning the process of evolution, whereas living species supply information on the product of evolution. Unfortunately, the fossil record is partial and fragmented, and often cannot support validations for specific evolutionary hypotheses. Living species can provide more comprehensive indications, but they do not represent ancestral groups or primitive forms. Macaques or chimpanzees are frequently used as proxy for human ancestral conditions, despite the fact they are divergent and specialized lineages, with their own biological features. Similarly, in paleoanthropology independent lineages (such as Neanderthals) should not be confused with ancestral modern human stages. In this comparative framework, paleoneurology deals with the analysis of the endocranial cavity in extinct species, in order to make inferences on brain evolution. A main target of this field is to distinguish the endocranial variations due to brain changes, from those due to cranial constraints. Digital anatomy and computed morphometrics have provided major advances in this field. However, brains and endocasts can be hard to analyze with geometrical models, because of uncertainties due to the localization of cortical landmarks and boundaries. The study of the evolution of the parietal cortex supplies an interesting case-study in which paleontological and neontological data can integrate and test evolutionary hypotheses based on multiple sources of evidence. The relationships with visuospatial functions and brain-body-tool integration stress further that the analysis of the cognitive system should go beyond the neural boundaries of the brain.

Discovering Hominins - Application of Medical Computed Tomography (CT) to Fossil-Bearing Rocks from the Site of Malapa, South Africa

In the South African context, computed tomography (CT) has been used applied to individually prepared fossils and small rocks containing fossils, but has not been utilized on large breccia blocks as a means of discovering fossils, and particularly fossil hominins. Previous attempts at CT imaging of rocks from other South African sites for this purpose yielded disappointing results. For this study, 109 fossil- bearing rocks from the site of Malapa, South Africa were scanned with medical CT prior to manual preparation. The resultant images were assessed for accuracy of fossil identification and characterization against the standard of manual preparation. The accurate identification of fossils, including those of early hominins, that were not visible on the surface of individual blocks, is shown to be possible. The discovery of unexpected fossils is reduced, thus lowering the potential that fossils could be damaged through accidental encounter during routine preparation, or even entirely missed. This study should significantly change the way fossil discovery, recovery and preparation is done in the South African context and has potential for application in other palaeontological situations. Medical CT imaging is shown to be reliable, readily available, cost effective and accurate in finding fossils within matrix conglomerates. Improvements in CT equipment and in CT image quality are such that medical CT is now a viable imaging modality for this palaeontological application.

Mapping connectivity damage in the case of Phineas Gage

White matter (WM) mapping of the human brain using neuroimaging techniques has gained considerable interest in the neuroscience community. Using diffusion weighted (DWI) and magnetic resonance imaging (MRI), WM fiber pathways between brain regions may be systematically assessed to make inferences concerning their role in normal brain function, influence on behavior, as well as concerning the consequences of network-level brain damage. In this paper, we investigate the detailed connectomics in a noted example of severe traumatic brain injury (TBI) which has proved important to and controversial in the history of neuroscience. We model the WM damage in the notable case of Phineas P. Gage, in whom a "tamping iron" was accidentally shot through his skull and brain, resulting in profound behavioral changes. The specific effects of this injury on Mr. Gage's WM connectivity have not previously been considered in detail. Using computed tomography (CT) image data of the Gage skull in conjunction with modern anatomical MRI and diffusion imaging data obtained in contemporary right handed male subjects (aged 25-36), we computationally simulate the passage of the iron through the skull on the basis of reported and observed skull fiducial landmarks and assess the extent of cortical gray matter (GM) and WM damage. Specifically, we find that while considerable damage was, indeed, localized to the left frontal cortex, the impact on measures of network connectedness between directly affected and other brain areas was profound, widespread, and a probable contributor to both the reported acute as well as long-term behavioral changes. Yet, while significantly affecting several likely network hubs, damage to Mr. Gage's WM network may not have been more severe than expected from that of a similarly sized "average" brain lesion. These results provide new insight into the remarkable brain injury experienced by this noteworthy patient.

Age-related changes of digital endocranial volume during human ontogeny: results from an osteological reference collection

Endocranial volume (EV) estimation is widely used in physical anthropology for assessing brain size differences between taxa and monitoring the emergence of brain growth patterns in modern humans. However, to date, no reference data are available for modern human EV ontogeny. We measured 94 skulls with known sex and age (ranging from 0 to 7.5 years) from the osteological collection of Strasbourg University (OCSU) by using an accurate digital active contour model algorithm on 3D virtual models, reconstructed by CT. The OCSU data also allow us to propose improved equations for estimating EV in immature individuals from dry skull diameters (length, width, and height). Aside from the EV, the average proportional endocranial volume (PEV), corresponding to the ratio of EV at a given age to the average EV in the corresponding adult population, was also computed. EV nearly doubles during the first year of life, and later continues to expand more slowly, at least until 7 years of age. No sex differences can be demonstrated between the EV distributions of boys and girls in this sample. However, although PEV at birth is identical in girls and boys, it later displays significantly higher values in the girls of our series. PEV obtained at birth is 22%, which is quite different from values established for the brain itself from autopsied individuals, or MRI data. This suggests that assessments of EV and PEV values in fossil specimens should be conducted by using identical measures in comparative samples of extant humans and apes.

Virtual endocasts: an application of computed tomography in the study of brain variation among hyenas

Reliable brain volume measurements are crucial in identifying factors that influence the course of brain evolution. Here, we demonstrate the potential for using virtual endocasts (VEs) to examine inter- and intraspecific variation in brain volume in members of the family Hyaenidae. Total endocranial volume (adjusted for body size) and anterior cerebrum volume (adjusted for endocranial volume) were greater in the spotted hyena, the most gregarious of the species, than in the other hyaenids, all of which are less gregarious. An intraspecific analysis of spotted hyenas revealed that anterior cerebrum volume is significantly larger in males than females, although total endocranial volume does not differ between the sexes. Greater total endocranial and anterior cerebrum volume of spotted hyenas, relative to those of other hyena species, may be related to increased neural processing mediating cognitive demands associated with a complex social life. These data demonstrate that computed tomographic (CT) technology can be used to create VEs in species for which actual brains are rare or unavailable, and suggest that this approach can be applied systematically to explore intra- and interspecies brain variations in studies of brain evolution.

Methodology for estimating endocranial capacity in a modern European population

Various methods have been published in the literature to estimate endocranial capacity. These are based on mathematical equations using measurements made directly on the skull or indirectly from X-rays, by filling the skull with various materials, by endocasts both physical and virtual (using 3D CT-scan reconstructions). Each method has its advantages, limits and drawbacks. A useful method is one that is simple, time-efficient, cheap, and reproducible. For this study we estimated endocranial capacity by filling the skull with calibrated glass beads. We used a thorough protocol of tamping to ensure results reproducibility. Intra- and inter-observer trials showed no significant differences. The method was applied to 130 recent French (West European) skulls (65 males and 65 females). Sexual dimorphism was studied using logistic regression functions, discriminant analysis, and neural network. The best results were obtained using the neural network, built with two hidden nodes in the hidden layer and one output node, and trained with a steepest descent algorithm. Our tests show that there is obvious sexual dimorphism (p < 10(-5)) of the weight of the skulls (623.44 ± 106.83 g in males; 548.07 ± 94.57 in females), the weight of the glass beads used to fill the skulls (2379.83 ± 228.92 g in males; 2095.95 ± 145.49 in females), and endocranial capacity (1676.47 cm(3) ± 161.26 in males; 1476.48 ± 102.49 in females), but overlapping between sexes is quite significant. The average ECC in male (1676.5 cm(3)) and in female (1476.5 cm(3)) subjects is higher than those previously published, which deserves some discussion.

The middle meningeal artery: from clinics to fossils

INTRODUCTION

Although research today ranges from molecular to universe scale, many issues regarding gross anatomy remain totally neglected. Within the framework of the endocranial morphogenesis and evolution, understanding the role and variation of the middle meningeal artery relies upon the very limited, scattered, and descriptive information available. The meninges are supplied by branches originating from both the internal and external carotid arteries, often converging in the same networks and hence raising questions on the homology and embryogenesis of these vessels. The middle meningeal artery is often ligated during craniotomies, with no apparent impairment of the cerebral functional processes. The exact physiological role of this extended vascular system, together with the adaptations and selective pressure associated with its evolutionary characterization, have generally been ignored.

THE MIDDLE MENINGEAL VESSELS IN NONHUMAN PRIMATES

Anthropologists have made many attempts to quantify and qualify the differences and variation between and within human and nonhuman primates, with scarce results due to the blurry morphology of the vascular networks. Living apes and humans probably have meningeal vessels originating from different embryogenetic processes, further hampering easy phylogenetic comparisons. Generally, monkeys and apes display a larger component derived from the internal carotid artery and its ophthalmic branch.

EVOLUTION AND MORPHOLOGICAL VARIATION IN FOSSIL HOMINIDS

The fossil endocasts partially show the traces of the middle meningeal vessels, allowing some hypotheses on the evolution of these structures. In contrast with modern humans, some extinct groups show a dominance of the posterior branch over the anterior one. The most interesting features are associated with the variation of the middle branch, which supplies the parietal areas. In any case, the most striking difference between the modern and non-modern humans regard the definite increase in the number and complexity of the anastomoses and reticulation in the former. This may be either the simple result of a larger percentage of traces left by the soft tissue or be associated with a more developed vascular network.

PERSPECTIVES

Tools are needed to quantify and qualify the morphogenesis and variations of the middle meningeal artery. Supposing these vessels are not strictly necessary in the adult age, the evolutionary pressure shaping their structure may have been associated with early life stages. Apart from oxygenation, another function which deserves attention is thermoregulation, considering the metabolic loadings of the cerebral mass.

Cranial shape and size variation in human evolution: structural and functional perspectives

A GLIMPSE INTO MODERN PALEOANTHROPOLOGY: In the last decades, paleoanthropology has been deeply modified, changing from a descriptive and historical science to a more quantitative and analytical discipline. The covariation of multiple traits is investigated to study the evolutionary changes of the underlying anatomical models, mostly through the introduction of digital biomedical imaging procedures and of computed geometrical analyses supported by multivariate statistics. FUNCTIONAL CRANIOLOGY: The evolution of the human cranium is consequently considered in terms of functional and structural relationships between its components, largely influenced by the allometric variations associated with the increase in the relative cranial capacity. In the human genus, the changes in the face, base, and neurocranium are characterised by a mosaic variation, in which adaptations, secondary consequences, and stochastic factors concur to generate a set of anatomical possibilities and constraints. SYSTEMIC PERSPECTIVES TO THE EVOLUTION OF THE HUMAN CRANIAL MORPHOLOGY: Concepts like morphological modularity, anatomical integration, and heterochrony represent key issues in the development of the current human evolutionary studies.