Category Archives: Anatomy

Skulls and brains in reptiles and birds

In a recent paper, Fabbri et al analyzed the relationship between brain and cranial vault shape in the transition from reptiles to birds. To assess the evolution of this relationship they used a broad sample including Aves, Lepidosauria, Crocodylia, Archosauria, and Reptilia. To assess developmental differences they included an ontogenetic sample of Alligator mississipiensis and Gallus gallus. The results showed that the relationship between the vault bones and the brain is conserved across these taxa, with the frontal bone positioned over the forebrain and the parietal bone over the midbrain or over midbrain and posterior forebrain. Nonetheless, they observed some shape variations, namely on the relative sizes of the frontal and parietal bones and in the position of the fronto-parietal suture relative to the forebrain-midbrain boundary. These two structures are significantly correlated, with the fronto-parietal suture being either anterior to (e.g. stem reptiles) or nearly aligned with (e.g. crown birds) the forebrain-midbrain boundary. In terms of ontogeny, chickens have a shorter ontogenetic trajectory than alligators, as the brain and skull of embryos are similar to the adult ones. The brain and skull of alligators develop with negative allometry, with the brain relatively large in early stages but becoming relatively small during growth. Conversely, the skull and brain of chicken grow with positive allometry, and the authors suggest the brain should be considered peramorphic in Aves. Overall the results stress the important role of the brain in shaping the cranial vault. The authors wonder whether the intimate relationship between brain and frontal and parietal bones is the key for the conservation of the cranial vault across vertebrates.

Sofia Pedro

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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


Primates brain shape

We have published one more paper on the morphology of the precuneus, this time featuring a sample of non-human primates, in collaboration with James Rilling and Todd Preuss from the Emory University (Atlanta, USA). Modern humans have a much larger precuneus than chimpanzees both in absolute and relative size. Taking into account the large brain size in our species, we investigated the midsagittal morphology in non-human primates as to test whether precuneus proportions are influenced by allometric factors. We did a geometric morphometric analysis on a total of 42 MRIs from the National chimpanzee brain resource database, including 5 species of apes and 4 species of monkeys. A first analysis, conducted on the species averages, showed that the main pattern of midsagittal variation involves the general shape of the braincase, which might be due to cranial constraints rather than to changes in proportions of specific brain regions. This main shape pattern separates monkeys from apes, as the former display flatter, elongated brains (with capuchins being the flattest), while the latter exhibit rounder brains with frontal bulging (especially orangutans). This morphological variation correlates with brain size, except for gorillas (which brain is large but elongated), and gibbons (which have smaller but round brains). A second analysis was conducted only on chimpanzees and macaques, to compare two species with different brain size. In neither case the proportions of the precuneus displayed major differences between species or size-related changes. However, as in humans, precuneus size is very variable within each species, suggesting a remarkable plasticity. Overall, the results suggest that precuneus expansion in modern humans is a species-specific characteristic of our species, rather than a simple consequence of increase in brain size. Further studies should address the histological and functional processes involved in this morphological change.

Sofia Pedro


Eye-brain spatial relationship

We have just published a new study on the spatial relationship between visual and endocranial structures in adult modern humans, chimpanzees, and fossil humans. The survey was conducted in collaboration with Michael Masters from Montana Tech (USA), who previously hypothesized that, in modern humans, the positioning of the orbits below the frontal lobes coupled with a reduced face could result in spatial conflict among ocular, cerebral, and craniofacial structures. This could lead to vision problems, such as myopia. In addition, another study evidenced that eye and orbit dimensions have a stronger correlation with the frontal lobes, rather than with the occipital lobes, indicating that the ocular structures can be more constrained by spatial (physical) than by functional (vision) relationships. In this study we used geometric morphometrics to investigate the longitudinal (antero-posterior) spatial relationships between orbito-ocular and endocranial structures. First, we addressed the the position of the eye relatively to the frontal and temporal cortex, on a sample of 63 modern humans’ MRIs. Second, we addressed the spatial relationship between orbital and endocranial structures on a CT sample comprising 30 modern humans, 3 chimpanzees, and 3 fossil humans (Bodo, Broken Hill 1, Gibraltar 1).

The results of the MRI analysis show that in adult modern humans the main pattern of shape variation deals with the antero-posterior position of the eye relative to the temporal lobes. Individuals which eyes are closer to the temporal lobes exhibit rounder frontal outline and antero-posterior shorter eyes, indicating a possible physical constraint associated with the spatial contiguity between the eye and the middle cranial fossa. A second pattern describes the supero-inferior position of the eye, relatively to the frontal lobe. Also in this case, proximity is apparently associated with slight changes in eye form. Individuals with larger volumes of the frontal and temporal lobes tend to have eyes located more posteriorly, closer to the temporal lobe, although with no apparent change in the shape of the eye. These results partially support Master’s hypothesis, suggesting reciprocal spatial patterns influencing brain and eye form.

When analyzing orbits and braincase through CT data, the main intra-specific variation among modern humans concerns the orientation of the orbit, not the position. Nonetheless, analyzing humans, apes, and fossil hominids all together, the main differences deal with the distance between orbits and braincase: they are separated in chimps, overlapped in modern humans, and in intermediate position in fossils. In this case, fossils belong to the hypodigm of Homo heidelbergensis. Modern humans are characterized by larger temporal lobes when compared with other living primates, and longer middle cranial fossa. The proximity with the eyeballs due to face reduction can stress further a morphogenetic spatial conflict between orbits and brain. Next step: 3D analyses, ontogenetic series, and vision impairment.

Sofia Pedro


Hominin biomechanics

 

Hominin biomechanics

Virtual anatomy and inner structural morphology,
from head to toe
A tribute to Laurent Puymerail

Comptes Rendus Palevol 16 (2017)

[ScienceDirect]

 


Vessels and neurosurgery

obrMagnetic Resonance Imaging (MRI) methods has a primary use in medicine, especially in diagnosis and image-guided surgery. In neuroscience, attention is mainly focused on the brain, and vessels are not always a target of the imaging procedures. The crucial aspect of using imaging during surgery concerns the correspondence with the real physical structures. This correspondence is affected by a displacement of the brain during surgery called brain shift, which can result in 5 – 10 mm difference from the MRI data. Several technical procedures are used in order to avoid this mismatch. Since intraoperative MRI devices are not always available, using local markers for orientation and navigation could be a plausible alternative. In a recent paper, Grabner and colleagues suggest to use the system of veins on the surface of the cerebral cortex as reference landmarks. These veins are well visible during the surgery, and can potentially improve navigation. The study is focused on developing a non-invasive MRI technique for the visualization of the superficial cortical veins and validation of that method by comparing MR images with high resolution photographs of human cadavers.

Considering Magnetic Resonance Angiography (MRA), the main concern of using this method is the use of a contrast agent, and the possibility of overlooking the superficial cortical veins because of the slow blood flow. Alternatively, the authors suggest to use Susceptibility-Weighted Imaging (SWI), which is a blood-oxygen-level dependent technique of MRI with an ability to image vessels smaller than a voxel. Gradient-echo based T2-weighted imaging was performed in this study using a 7 Tesla MRI scanner. Image processing relied on automated vessel segmentation and overlaid on anatomical MRI. The results showed high correlation between segmented veins in MRI and actual venous anatomy of the sample, and therefore surface venograms could serve as alternative navigation system for neurosurgery.

Reliable methods of imaging and segmentation of vessels are valuable also in theoretical fields, where those methods could contribute to the investigation of the function of the endocranial venous system. The importance of the veins is usually estimated according to their size, although functional information on these vessels is still scanty, and methodological research to improve craniovascular studies can be beneficial in both anthropology and medicine.

Stáňa Eisová


Microgravity and sensorimotor function

Space missions can have adverse effects on astronauts, such as the already-mentioned vision deterioration and cognitive impairment. Spending a long time on space can also impact sensorimotor function. Koppelmans et al. have recently investigated the influence of microgravity environment on sensorimotor performance and brain structure. They conducted a longitudinal study with a group of male subjects remaining in a 6-degrees head down tilt bed rest (HDBR) position, an analog environment to study the effects of spaceflight microgravity, during 70 days. MR images were collected before, during, and after HDBR, to explore changes in gray matter (GM) volume, and functional mobility and postural equilibrium tests were conducted pre- and post-HDBR, to check sensorimotor performance. For control, they used data from other subjects who had completed the same measurements at four different times over 90 days for another study, not being exposed to HDBR. Relative to controls, the HDBR subjects showed widespread changes in GM volume, as the percent of brain volume, from pre- to the last assessment during HDBR. More specifically, GM volume increased in the posterior parietal region and decreased in the fronto-temporal regions, and these changes are strongly correlated. The sensorimotor performance was decreased in HDBR subjects from pre- to post-HDBR, as they needed more time to complete the test, while controls showed no difference in performance. Following the HDBR period, both GM volume and sensorimotor changes started to recover, though not totally 12 days later. Regarding the association between brain and behavior, researchers found that larger increases in GM volume in precuneus and pre- and postcentral gyri correlated with better balance performance, though not significantly after Bonferroni correction. They propose these changes in GM volume might reflect cortical plasticity as an adaptive response to alterations in somatosensory input caused by HDBR position. The observed patterns of GM change could also be explained by alterations in intracranial fluids distribution and pressure due to posture, though this hypothesis would need further examination. The authors conclude their findings match the sensorimotor deterioration observed in astronauts, but are also of interest for individuals who are temporarily or permanently confined to a bed and will probably experience the same GM and sensorimotor alterations.

Sofia Pedro


Cortical and scalp development

In a recent study, Tsuzuki and colleagues analysed the co-development of the brain and head surfaces during the first two years of life using a sample of 16 infant MRIs, aged from 3 to 22 months. First, they digitized a set of cortical landmarks defined by the major sulci. Then they determined the position of cranial landmarks according to the 10-10 system, a standard method to place electrodes for electroencephalography, using  nasion, inion, and the pre-auriculars as a reference. Besides analysing the spatial variability of the cortical and scalp landmarks with age, they compared the variability of the cortical landmarks to the 10-10 positions, in order to evaluate the validity of the scalp system as a reference for brain development. For that, they transferred a given cortical landmark to the head surface by expressing its position as a composition of vectors in reference to the midpoint between the two pre-auriculars and to the three neighbor 10-10 points. The scalp-transferred landmarks were then transformed to the scalp template of a 12-month-old infant and depicted in reference to the 10-10 system.

Age-related changes in the cortical landmarks were most obvious in the prefrontal and parietal regions. As the brain elongates, the frontal lobe shifts anteriorly and the precentral gyri widen. In addition, the intraparietal sulci and the posterior part of the left Sylvian fissure move forward, suggesting relative enlargement of the parietal region in the anterior direction. The same result was obtained by our team by analyzing cranial and brain landmarks in adults: larger brain size is associated with a relative forward position of the parietal lobe. The scalp showed relative anteroposterior elongation and lateral narrowing with growth. Regarding the contrast between the cortical landmarks and the 10-10 system, the authors observed that the variability in the position of the former was much smaller than the area defined by 10-10 landmarks, indicating this system can be useful to predict the underlying cortical structures. Hence, they conclude that the changes in brain shape during development are well described by cortical landmarks and that the relative scalp positioning based on the 10-10 system can adjust to preserve the correspondence between the scalp and the cortical surfaces.

 

Sofia Pedro


What the brain’s wiring looks like

The world’s most detailed scan of the brain’s internal wiring has been produced by scientists at Cardiff University. The MRI machine reveals the fibres which carry all the brain’s thought processes. It’s been done in Cardiff, Nottingham, Cambridge and Stockport, as well as London England and London Ontario. Doctors hope it will help increase understanding of a range of neurological disorders and could be used instead of invasive biopsies …

[keep on reading this article by Fergus Walsh on BBC News]


Brain partition scaling

A group coordinated by Dr. Vera Weisbecker examined whether the evolution of mammalian brain partitions follows conserved developmental constraints, causing the brain to evolve as an integrated unit in which the partitions scale with brain size. According to this ‘late equals large’ hypothesis, the timing of neurogenesis predicts the size of the partition such that later and more extended neurogenesis produces larger partitions due to the production of more neural precursors. In order to investigate the impact of neurogenesis on patterns of brain partition growth, the volumes of the whole brain and major partitions were reconstructed from soft-tissue diceCT scans of three marsupial species, including individuals with ages ranging from 1 day to adulthood. They tested three hypotheses consistent with a conserved brain partition growth: H1 postulates that partition scaling during development reflects the evolutionary partition scaling, and thus growth patterns should be uniform between species; H2 assumes that a neurogenesis-driven pattern of partition scaling is predictable from adult brain size, i.e. brain partitions scale with brain size; and H3 states that growth with age might differ between species according to brain size and/or neurogenetic events. Regressions of log partition volume against log rest-of-the-brain volume (whole-brain volume minus partition volume) showed significant interspecific differences in slopes and intercepts of most brain partitions, indicating diverse scaling patterns between species, which could not be predicted by adult brain size, as the smallest-brained species had intermediate slope to the other two.  Growth curves of log partition volume against age were similar in all partitions within-species, but differed between species, particularly in growth rates, with the species with intermediate brain size having slower rates than the other two. Differences in growth patterns do not seem to be related to neurogenetic schedule as largest partitions are not especially late in their development and important maturation processes, like eye opening, occur closer to the end of the growth phase. Thus, none of the hypotheses are supported by these results, challenging the conserved neurogenetic schedules behind the evolution of mammal brain partitions. Moreover, the authors found high phylogenetic signal in brain partition scaling, revealing that a large part of the scaling relationship between brain and partition volumes is explained by phylogeny, which is more in agreement with a mosaic evolution of brain partition sizes, stressing its biological meaning and the level of mammalian brain plasticity. However, the intraspecific regular partition growth curves led the authors to contemplate the existence of an early brain partition pattern regulated by regional gene expression, and propose that further studies of brain partition evolution should integrate developmental neuromere expression models, neuron density, and patterns of neuron migration.

 

Sofia Pedro