Author Archives: gizehrangeldelazaro

Selective brain cooling in modern humans

The human brain is the most expensive and costly organ in terms of energetic resources and management. However, the current understanding of its sophisticated thermal control mechanisms remains insufficient. Wang et al., 2016, have reviewed the most recent studies on brain thermoregulation and examined the anatomical and physiological elements associated with selective brain cooling. Modern humans have a brain that is approximately three times larger than a primate with a similar body size, which uses 20%– 25% of the total body energy compared with a maximum of 10% in other primates and 5% in other mammals. The evolution of a large and expensive brain in modern humans effectively influences critical factors such as temperature, and functional limits can affect cerebral complexity and neural processes. Brain thermoregulation depends on many anatomical components and physiological processes, and it is sensitive to various behavioral and pathological factors, which have specific relevance for clinical applications and human evolution. The anatomical structures protecting the brain, such as the human calvaria, the scalp, and the endocranial vascular system, act as a thermal interface, which collectively maintains and shield the brain from heat challenges, and preserves a stable equilibrium between heat production and dissipation. Future advances in biomedical imaging techniques would allow a better understanding of the physiological and anatomical responses related to the cerebral heat management and brain temperature in modern humans.

Gizéh Rangel de Lázaro

 

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Sexual identification

post1Sex assessment is crucial in any survey on human remains.  Musilová et al, have recently published a new method for sexual identification using virtual scans of both male and female individuals. They found that the size of the cranial surface was significantly different between both sexes, being the male skulls larger than the females in some areas, such as the nasal root, external occipital protuberance and mastoids. The most pronounced areas with sexual cranial differences are those linked to muscle attachment, such as supraorbital, frontal and nuchal regions. Sexual dimorphism was significantly lower in senile skulls. This article provides a new and successful method using 3D techniques and geometric morphometrics, interesting for different applications in anthropology.

Gizéh Rangel de Lázaro


Mapping the brain

The Rhoton Collection is composed by an outstanding anatomical presentations of the brain created by the renowned surgeon and educator Dr. Albert Rhoton Jr throughout his life. These presentations were made using bright blue and red dyes in the blood vessels, so that surgeons could easily visualize and explore the brain and vascular structures for planning surgical interventions.

[Here a post in Spanish]

Gizéh Rangel de Lázaro


Cranial thickness

estimation-of-skull-table-thicknessThe cranial vault is composed by three bone layers (inner table, diploe, outer table), and its principal function is to safeguard the brain from impacts. Bone thickness is a crucial parameter to understand the biomechanical factors contributing to skull deformations and fractures after head injury. It is therefore  important to establish an accurate measurement system to quantify its variation. Lillie et al., 2015 analyzed microCT scans of two cadavers to evaluate the accuracy of the estimated cortical thickness from clinical CT data. Microscans were acquired at 25-microns, while CT scans had a resolution of 0.48-0.62 mm. The skull average thickness in both cases was below 4 mm. Cortical thickness measurements obtained from CT scans are more accurate compared with traditional physical methods, although results are comparable with those available in literature. The average cortical thickness discrepancy between microCT scans (higher resolution) and CT scans (lower resolution) is 0.078+ 0.58 mm. Such methodological validation is necessary when dealing with age-related changes in distribution of the skull cortical thickness, and to identify species-specific or population differences.

Gizéh Rangel de Lázaro


Free skulls!

human-skull2Lynn Copes has posted online 705 cranial CT scans of modern humans for free download. The dataset is part of her PhD sample which comes from archaeological sites in Alaska, Greenland and Oceania, from the Terry Collection (a cadaver-based collection from the United States). The original skulls are deposited in the National Museum of Natural History (Washington, DC), and the Point Hope Alaska Collection at the American Museum of Natural History (New York, NY). Lynn Copes is on Google Scholar and Twitter.

Gizéh Rangel de Lázaro


Growth and development of the human crania

The human craniofacial morphology changes rapidly from birth to adulthood. The skull is a complex structure that undergoes significant changes in size and propositions throughout life. The video created by Beatrice Lau, is an excellent didactic resource to understand the human craniofacial growth and development.

Gizéh Rangel de Lázaro


The diploic vascular channels

Gizéh diploic veinsThe diploic channels are placed between the vault cortical layers (external and internal). The calvarial diploe contains large and valveless diploic veins interconnected through a complex network of microscopic channels. We have now published a procedure for segmentation of diploic channels and localization of the main vessel pathways by reducing the noise of the cancellous bone. We also provide quantitative description of the diploic vessel variation in modern humans and three Neanderthals. One modern human was reformatted at three different resolutions namely high, medium and low, to estimate the effect of the pixel resolution on the final anatomical rendering. The use of computed tomography at high resolution can hamper semi-automatic segmentation of the diploic channels. Optimal resolution should be sufficient to reveal the channels without increasing noise associated with the trabecular structure. We have found that modern humans present a remarkable variation of diploic channels in their morphological patterns, being the parietal area the most vascularized. There is a correlation in the degree of vascularization of the frontal, parietal, and occipital bone, and no asymmetries can be apparently detected. The three Neanderthals analyzed in the study also display a parietal vascular network, but less developed than modern human, suggesting these vessels may be involved in evolutionary changes. The diploic network is commonly connected with the meningeal artery at the temporal fossa, with the emissary veins at the occipital bone, and with the venous sinuses at the parieto-occipital areas. The brain and braincase of our specie are characterized by larger parietal areas, and changes in the vascular organization can be associated with thermoregulation and heat management. In this sense future research may help us to understand the possible involvement of the diploic veins in brain thermoregulation. The study of diploic channels may be relevant in anthropology, medicine, paleontology, and forensic sciences.

Gizéh Rangel de Lázaro


Ontogenetic changes in human crania

cranial-growth-postThe brain growth pattern in humans is distinctive among primates. In the past decades several hypotheses have been proposed to analyze cranial ontogenetic changes (i.e shape and size variations) in humans (e.g. Moss and Young, 1960; Lieberman et al., 2002; Bruner, 2004; Neubauer et al., 2009). The recent study conducted by García Gil et al. (2015) presents a preliminary approach to the histological variations of the vault bones in three individuals of different ages (child, adolescent and young adult). According to their results, it is possible to identify three different histological phases of cranial growth. In the child, vault bones are primarily composed of avascular lamellar bone (widely vascularized). In contrast, the adolescent bones show a larger extension of mineralized regions (highly remodeled areas) and low levels of vascularization, with a much reduced diploe. In the adult, the vault bone is highly vascularized and the diploe is largely expanded. The authors suggest that the sealing of the cranial bone surfaces helps to minimize the bone porosity while increases bone expansion (during childhood) and thickness (during youth). This “sealing process” could play a main role controlling head thermoregulation until the brain finishes its maturation. When confirmed on larger samples, these results can introduce new perspectives in functional craniology.

Gizéh Rangel de Lázaro


A new human species

Untitled-3Berger et al., 2015 recently reported a new species called Homo naledi, found at the Dinaledi Chamber in the Rising Star cave system in South Africa. This species present a mosaic of several anatomical features from Australopithecus and Homo species. The fossil remains correspond to 15 individuals from the same species. The age of the fossils remain unclear. The researchers presented a detailed comparative analysis between H. naledi and other species. They affirm that the overall morphology of H. naledi is more close to humans than to australopiths. The cranium lacks primitive features like well developed sagittal and nuchal crests. In this sense, H. naledi cranial morphology is more similar to other extinct human species that lived between four million and two million years ago, namely H. erectus, H. habilis, and H. rudolfensis. Homo skull traits include frontal and parietal bossing, cranial bones relatively thin (like H. habilis), flexed occipital and transverse torus (like H. erectus), the supraorbital torus well developed and weakly arched (as H. erectus and H. habilis)  and gracile mandible; as well as their body mass and stature, are consistent with small bodied human populations, namely the lower limb, the foot and the ankle. However, Homo naledi fossils, presents some australopith-like characters as small endocranial volume (560-465 cc) and the morphology of the postcranial skeleton (trunk, shoulder, pelvis and proximal femur). Berger et al., suggest that the combination of different features presented in H. naledi is the result of a complex, and probably, polyphyletic process of different species that evolved separately in Africa.

Gizéh Rangel de Lázaro


Open-access 3D morphological datasets

morphosourceMorphoSource, is a dataset project for storing, collaborative sharing, and distribution of microCT scans, 3D surface rendering, and 2D digital imaging. Its main goal is to provide rapid access to as many researchers as possible, large numbers of raw microCT data, and surface meshes representing vouchered specimens. The site is active since April 2013 and now hosts almost 5000 files, including ‘raw’ microCT volumetric data, mesh files  from laser scans, and 2D digital photographs (file formats include tiff, dicom, stanford ply, and stl). MorphoSource, allow to download a world-wide repository-vouchered digitalized specimens from 48 institutions (American Museum of Natural History; Muséum National d’Histoire Naturelle; Natural History Museum Vienna, see more in Institutions). Currently the amount of information related with genus Homo is limited to Homo sapiens; however the site dataset is growing rapidly, and in the future it will be an interesting source of data for Paleoanthropologists too.

Gizéh Rangel de Lázaro