Author Archives: Alannah Pearson

About Alannah Pearson

PhD candidate at the Australian National University investigating changes to skull and brain form in fossil and living primates

Modelling brain-skull interface

Precise computational modelling of the brain-skull interface is necessary for the prediction, prevention and treatment of acquired brain-injuries. The brain-skull interface comprises complex layers including the osseous cranial tissues, meninges, sub-arachnoidal space and tissues, cerebrospinal fluid (CSF), pia mater and the gray and white cerebral matter. While the tissue properties of the brain-skull interface are known, there is no consensus on how these layers interact during head impact.  To generate computational models of the brain-skull interface with greater accuracy, knowing the boundary conditions or constraints is necessary. Previous experimental studies have relied on modelling the deformation of the brain-skull interface using neural density targets (NDTs) implanted into the cadaver brain, collecting information on tissue displacement during front and rear impact in motor vehicle crash-tests.

Wang et al. (2018) utilized computational bio-mechanics and finite element analysis (FEA), placing nodes in the 3D model in close approximation to the position of the experimental NDTs. Four hypotheses of the brain-skull interface were modeled, each approach placing different boundary conditions to model deformation during simulated head impact. All analyses were validated against previous experimental studies. Results showed that how the brain-skull interface was modeled appreciably affected the results. The 3D model showing the closest agreement with the experimental data, included all tissues of the brain-skull interface, allowed for displacement without separation of the skull and brain tissues, and strongly corresponded with known neuroanatomy. This 3D model indicated that non-linear stress-strain associations between brain and skull tissues best matched experimental results. Further, this 3D model could be closely predicted using an Ogden Hyperviscoelastic Constitutive model which did not over- or under-estimate deformations during head impact. The risks of over- and under-estimating head impact during motor vehicle accidents has implications for vehicle construction and prevention of serious brain trauma during accidents. Ultimately, a better understanding of the interaction between layers of the brain-skull interface can produce more accurate predictions of the likely impact during motor vehicle accidents and prevent violent head injury. Extrapolation of this research into paleoneurology could allow investigations into the structural interaction between the brain and braincase, testing if the resistence of brain-skull tissues during deformation evolved in human species as primary adaptations or secondary adjustments such as allometric responses.

 

Alannah Pearson

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A History of Surgery

The Chirurgeon’s Apprentice is a popular blog on the website of medical historian Dr Lindsey Fitzharris who received her doctorate from University of Oxford in medical, technology and science history. Dr Fitzharris discusses the apt naming of the blog with the word ‘chirurgeon‘ the first historical reference to a practitioner of surgery. The website illuminates the often grisly but fascinating historical developments in Medicine and Surgery with focus on the Victorian era and the rapidly developing techniques and methods occurring in all scientific disciplines at this time.  Under the Knife is a well-researched and often darkly humorous video series delivered by Fitzharris where each episode details different aspects of the history of Surgery and Medicine. Dr Lindsey Fitzharris is also the author of a recent book The Butchering Art about the Victorian surgical pioneer Jospeh Lister and the development of antiseptic practices.

Alannah Pearson


Chimpanzee Sulci

Studying the evolution of brain form requires paleoneruologists to rely on casts from the cranial cavity from fossil species. Due to the lack of soft-tissue preservation in fossils, descriptions of macroanatomy and cytoarchitecture  are taken from comparative non-human primates to serve as hypothetical models of early hominin brain form. Using extant non-human primates as models for fossil species ignores the separation of lineages, any specific adaptations and lineage-specific evolution since divergence. Furthermore, extant species risk being relegated as ‘living fossils’ with the issue worsened by the absence of identifiable fossils for either Pan or Gorilla. The untenable assumption is that extant chimpanzee anatomy should resembles  the original form prior to the PanHomo split. Nonetheless, comparison among living hominoids is still mandatory to investigate the evolutionary radiation of this taxon.

Previous published descriptions of chimpanzee sulcal patterns occur in classic literature but were based on only a few post-mortem dissections. Recently, Falk and colleagues aimed to increase knowledge of chimpanzee sulcal variation by describing sulcal patterns present in in-vivo Magnetic Resonance Imaging (MRI) from eight chimpanzees. Results suggested that, contrary to previous opinion, two sulci do occur in both chimpanzees and humans. To elaborate, these two sulci are the middle-frontal sulcus located in the frontal lobe, and lunate sulcus located between the parietal and occipital lobes.

No quantitative analyses were conducted in this study, but Falk et al. (2018) provide detailed descriptions of the variation between individuals, highlighting why descriptions based on only one or two individuals cannot be used to reliably describe the brain anatomy of a species. The authors argue the presence of the middle-frontal sulcus and lunate sulcus in chimpanzees invalidates previous claims that these sulci represent derived states found only in the human lineage. Further quantitative analyses with much larger samples, including both extant and fossil species will aid in a better understanding of the brain anatomy of humans and other great ape species.

Alannah Pearson


Fossil Primate Brains

Primates are unique among mammals for having a brain much larger than expected for body size. An important  aim in paleoneurology is  understanding how cerebral structures reorganized to accomodate primate cerebral expansion. The brain comprises only soft-tissue and does not fossilize  so paleoneurologists rely on endocasts, either physical or digital molds of the cranial cavity, to estimate the macro-anatomy of the brain. Continuing computational advances and powerful imaging techniques have allowed the generation of increasingly higher-resolution digital endocasts. Gonzales et al. (2015) generated a high-resolution endocast of the 15 Myr-old fossil cercopithecine Victoriapithecus macinnesi using micro-CT scans. By using computational methods, taphonomic distortion was corrected and a new endocranial volume (ECV)  of 35.6 cm3 reported for Victoriapithecus which is much smaller than the previous value 54 cm3. This new, smaller ECV places  Victoriapithecus within the range of extant strepsirrhines but outside the range expected of extant and fossil cercopithecoids including the 32 Myr-old fossil species Aegyptopithecus zeuxis which had an ECV within the expected range for fossil cercopithecoids.

Despite Victoriapithecus exhibiting a very small ECV and falling below the range for extant cercopithecoids, the fossil does exhibit the ‘frog-shaped’ sulcal pattern shared only among cercopithecines. This sulcal pattern suggests Victoriapithecus is a cercopithecine, the ‘frog-shaped’ sulcal pattern is such a diagnostic trait that it is not shared by the leaf-eating colobines but only present in cercopithecines. The olfactory bulbs in Victoriapithecus are unusually large relative to the small ECV. Large olfactory bulbs are present in extant strepsirrhines and the fossil catarrhine Aegyptopithecus zeuxis but reduced in all extant and fossil cercopithecoids and hominoids. The presence of small olfactory bulbs in the 18 Myr-old hominoid Proconsul versus the large bulbs in  Victoriapithecus suggested olfactory bulb reduction may have evolved independently in both cercopithecoids and hominoids.

Harrington et al. (2016) compared digital endocasts generated from micro-CT of three adapiform fossil primates including the 48 Myr-old Notharctus tenebrosus, 47 Myr-old Smilodectes gracilis and 45 Myr-old Adapis parisiensis. Results of endocranial volume (ECV) were consistent with other studies revealing an ECV of 7.6 cm3 for Notharctus, an ECV of 8.3 cm3 for Smilodectes while Adapis had an ECV of 8.8 cm3. The sulcal morphology of these adapiforms was also consistent with previous studies showing the defining feature of the primate brain, the Sylvian sulcus, is species-specific in these adapiforms. The Sylvian sulcus is well-defined in Adapis, occurs only as a shallow depression in Notharctus but is entirely lacking in Smilodectes. The absence of the Sylvian sulcus in Smilodectes is not understood but as it is absent in other mammals, this may represent a retained ancestral trait from before the divergence of primates from other mammals.

The cerebral organization of Notharctus and Smilodectes showed both possessed larger temporal and occipital lobes relative to brain size with smaller olfactory bulbs and frontal lobes. This trend might indicate cerebral reorganization favoring larger visual-auditory structures located in the temporal-occipital regions of the brain versus smaller visual-olfactory structures in the frontal region. The olfactory bulbs of these adapiforms were small and blunt relative to endocranial volume and predicted body mass but uniquely, Adapis parisiensis had the largest olfactory bulbs, placing it within the range of extant strepsirrhines. These studies reveal how little is understood about primate paleoneurology and the evolutionary trends of different primate lineages with implications for the human fossil record.

Alannah Pearson


Brain and Muscles

Among mammals, primates exhibit a trend toward increasing encephalisation. Attempts to explain the development of this trend focus on the energetic and metabolic trade-offs required to increase brain mass. The most widely discussed are variants of the Expensive Tissue Hypothesis (ETH) which proposes for any increase in brain mass other metabolically expensive tissues must decrease in size. The brain is metabolically costly with primates having larger brain sizes than other mammals and devoting up to 20% more basal metabolic rate to brain maintenance. Brain maintenance relies on aerobic cellular respiration processes, thus requiring oxygen to efficiently function. In a resting-state, up to 90% of brain maintenance is sourced from aerobic respiration. The brain does not source oxygen directly but relies on aerobic cellular respiration, converting glucose into adenosine triphosphate (ATP) to produce energy. In humans, the brain consumes, on average, around 30% of total glucose allocation. Skeletal muscle is another expensive tissue type. Muscle consumes up to 30% of resting energy expenditure with nearly 100-fold increase during high activity. Mammals have nearly 50% of their total body mass accounted for by muscle mass while primates have only 35% of total body mass accounted for by muscle mass. Of primates, humans possess 50% less muscle mass than expected for body size. Skeletal muscle comprises a mixture of fibers known as Type I (slow-twitch for prolonged activity) and Type II (fast-twitch for short, sudden activity). Both fiber types require constant oxygen supply and glucose to convert to ATP via mitochondria. Although Type II fibers consume a higher net-amount of glucose than Type I, this is done for short periods of time. Type I fibers used for prolonged activities possess greater capillary density and more mitochondria than Type II, potentially allowing significantly more efficient conversion of glucose to ATP. This could suggest muscle mass is in direct competition with the brain through glucose requirement and that any increase in brain size could require a corresponding decrease in muscle mass as evidenced in primates, especially humans.

Muchlinski et al. (2018) examined the potential trade-off between muscle mass and brain size in non-human primates. Several skeletal muscles were dissected from primate cadavers and immunohistochemistry used to isolate muscle fiber types. Body mass strongly influenced endocranial volume and muscle mass in the primate species so variables were size adjusted. Results indicated an increase in endocranial volume was associated with a decrease in muscle mass. Type I muscle fibers were negatively correlated with endocranial volume but a positive correlation between Type II and endocranial volume was not statistically significant. In general, the primates sampled possessed more Type II than Type I muscle fibers. These results are encouraging but potential bias could be introduced from the small sample size and muscle selection with larger postural and locomotor muscles, erector spinae and scalenes, not examined as the minimum sample content for immunohistochemistry could not be dissected in very small primate species. The use of published literature for endocranial volumes and body mass may introduce additional issues. Despite this, the assumption that muscle may be in direct competition with the brain appears metabolically and energetically viable and a potential avenue for proper consideration in evolutionary primatology.

Alannah Pearson


Primate Cranial Complexes

The primate skull is comprised of complexes including the cranial base, vault and facial region. How these complexes respond to different developmental and growth processes as well as varied selective pressures like diet, locomotion and sexual selection have been investigated in terms of modularity and integration. The concepts of modularity and integration concern the co-variance or independence of these complexes.

Profico et al. used several recent statistical methods to test previous research conclusions suggesting the primate cranial base and facial complex are strongly integrated. The cranium from 11 extant species of the Cercopithecoidea and Hominoidea were studied utilizing geometric morphometrics to investigate shape variation, the presence of evolutionary allometry and modularity or integration.

Shape variation of the primate cranial base and facial complex was assessed by Principal Component Analysis. Among taxa, shape variation of the cranial base reflected patterns in locomotion, cranial base flexion and the size of the foramen magnum. The shape variation of the facial complex reflected size-related and sex-linked morphology, the degree of lower and mid-facial prognathism and associated changes to narrowing of the nasal-orbital regions. Evolutionary allometry was tested by multivariate regression of size on shape and indicated the facial complex but not the cranial base was influenced by evolutionary allometry. Modularity and integration was analyzed using Partial Least Squares to test the degree of co-variation between the facial complex and cranial base which proved to be low. These combined results suggested the cranial base and facial complex complied with the concept of modularity rather than integration contrasting with previous studies.

An important reminder that although a pattern of similarity was found between Pongo pygmaeus and Hylobates lar this does not imply a close biological relationship, rather these taxa share similar cranial base and facial block morphology, potentially as a by-product of orthograde posture and the absence of quadrupedalism found in the other primate taxa with the exception of modern humans which are obligate bipeds. In light of the current findings, a more comprehensive reconsideration may be necessary of the effects from variation in the facial complex and cranial base morphology throughout primate evolution.

Alannah Pearson


Colin Groves (1942-2017)

Colin Groves (2017)

Emeritus Professor Colin Groves was an internationally-recognized and respected taxonomist in Mammalogy and Primatology. After completing his PhD dissertation at University College London in 1966 on Gorilla skull variation and taxonomy, Colin was appointed as lecturer at the Australian National University (ANU). Colin was an integral part of the ANU Biological Anthropology Department, welcoming discussions with internationally recognized researchers and undergraduate students alike, always made himself available and believed in an “open-door” policy for teaching. For me, he was an inspirational and influential mentor, teacher, colleague and friend who was an irreplaceable part of the Australian and International Primatology and Anthropology community. An online condolence book has been organised for those wishing to pay their respects.

Alannah Pearson


Digital Anatomy Education Tools

Educational medical resources provided by IMAIOS include interactive atlases and tools. The human e-Anatomy atlas combines digital imaging and computational tools for all anatomical regions from the human brain , with 3D reconstruction and labeling of neuroanatomical features, extending to the human pelvic girdle with 3D reconstructions of bones and arteries. Subscription to these utilities is useful for healthcare professionals but is focused on educational institutions and lecturers with access available for students enrolled in courses. For educational purposes, the resource includes quiz templates for each anatomical region and a virtual environment with enjoyable but educational tools for human lower limb anatomy using the Ninja Lower Limb game. The inclusion of resources for Veterinary Medicine with the vet-Anatomy atlas in similar design as the Human e-Anatomy atlas. All these tools are accessible through computer access and common mobile and tablet platforms in multiple languages.

Alannah Pearson


Modelling Skull Growth

The Finite Element (FE) method has increasing application to biological sciences but frequently lacks proper validation by robust experimental research. One aspect of particular biological and bio-mechanical importance is growth of the human infant skull. Specific local changes during growth of the infant skull are largely unknown with only the general rate of cranial increase from 25% at birth to 65% of the adult size by age six. The potential adverse effects of any abnormalities in infant skull growth is difficult to approximate if the isolated local areas likely to be most impacted are not accurately known. If properly validated, computer simulated modelling such as Finite Element methods would be invaluable in surgical settings. A new comprehensive study focusing on human infant cranial vault expansion utilized robust laboratory experiments of a fetal skull (ex-vivo), replicate physical model (in-vitro), several FE models (in-silico) and a sample of micro-CT infant skulls (in-vivo). The first validation tested a physical model against a FE model (A) in which the cranial base and facial bones formed a single structure with only the cranial vault comprising individual bones. The FE model (A) over-predicted size changes to the anterior of the skull especially near the orbits and mediolateral expansion of the skull. The second validation tested in-vivo models against an FE model (B) in which the only the facial bones formed a single structure while the vault and cranial base comprised individual bones. All analyses associated discrepancy between the FE model (B) and the in-vivo models with age-related changes. As age increased, the regions under-predicted by the FE model (B) were first the orbits and upper vault before tending toward the cranial base, while the regions over-predicted by the FE model (B) were focused on the anterior and posterior fontanelles.

This validation study showed that FE modelling could be used to approximate growth in the human skull with only small discrepancies. The differences between the predicted ranges of growth (FE models) and the observed growth (in-vivo models) was explained by assumption of isotropic brain expansion which simplified the highly complex and uneven growth rates in real brain expansion. The artificial construction of a single structure representing the facial bones added further constraints. The development of more advanced simulations could narrow the discrepancy between expected and observed growth patterns allowing a more accurate representation of human skull growth.

Alannah Pearson

 


Primatology Encyclopedia

 The International Encyclopedia of Primatology, a new multi-volume resource suited to an academic audience studying human and non-human primates with topics on evolutionary biology, genetics, behaviour, taxonomy and ecology.

Alannah Pearson