Brainstorming today at the Laboratory of Hominid Paleoneurobiology! Talks and chats on several doctoral projects, integrating brain anatomy, functional craniology, vascular morphology and cognitive archaeology. From the left: Emiliano Bruner, Gizéh Rangel de Lázaro, María Silva Gago, Annapaola Fedato, Alannah Pearson, and Sofia Pereira-Pedro.
Virtual anatomy and inner structural morphology,
from head to toe
A tribute to Laurent Puymerail
Comptes Rendus Palevol 16 (2017)
Magnetic 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.
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.
A new PhD student in the team working on craniovascular anatomy! Stanislava Eisová was in our laboratory few years ago, publishing a paper on parietal bone and vessels in which she investigated correlations between craniovascular morphology, skull size, and bone thickness. She got a Master Degree in Anthropology of Past Populations at the University of West Bohemia, Czech Republic. Now she begins a PhD program on Anthropology and Human Genetics at the Faculty of Science of the Charles University, Prague. Her project will be on craniovascular traits, anthropology, paleoanthropology, and paleopathology. She will investigate craniovascular characters in normal samples, pathological conditions, and fossil specimens. The project is co-directed by Petr Velemínský.
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.
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]
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.
A perspective review on cerebellum and Alzheimer’s disease, coordinated by Heidi Jacobs …
Jacobs H.I., Hopkins D.A., Mayrhofer H.C., Bruner E., van Leeuwen F.W., Raaijmakers W., Schmahmann J.D.
The cerebellum in Alzheimer’s disease: evaluating its role in cognitive decline.
(and here a post on cerebellum and paleoneurology …)