The diagnosis of human brain abnormalities depends on knowing the norm and yet defining the range of normal variation is still far from resolved. Understanding what is within the normal human range has been limited by samples and the constraints of producing accurate brain mapping. Access to large brain imaging databases has been possible for a while but producing reliable atlases of key structures including folding patterns (sulci, gyri and fundii), volumes and major shape changes has not had large enough sample sizes to reliably grasp the range of normal brain variation. Current approaches have relied on highly skilled professionals to assess neuroanatomy. While this approach is adequate, it does introduce an inherent level of subjectivity and potential bias with each neuroanatomist dependent on the individual level of experience. To begin reducing this error while increasing sample sizes, new computational technologies allow more automated imaging processes that combine speed and quality.
Mindboggle is a new software platform recently released after development through a long-term research project addressing a need for integrating morphometry (measurements of morphology) to assess the quantitative differences in brain structure. Mindboggle relies on specially developed algorithms to segment brain tissue in MRI images, produce volumetric and structural parallelization of the brain and asses shape variation. Klein and colleagues highlighted issues with similar algorithm-based software that produced errors in segmenting brain from non-brain tissue. Freesurfer was shown to underestimate grey matter while overestimating white matter, while ANTs included more grey matter yet sometimes excluded white matter that extended deep in gyral folds. To resolve this issue, Mindboggle employed a hybrid algorithm that overlays the Freesurfer and ANTs segmentation imaging then combines these to produce a more faithful imaging set negating any errors in volume estimates, folding patterns or shape differences. Further results indicated the geodesic algorithm produced an exaggerated depth for brain regions like the insula, while the time depth algorithm unique to Mindboggle produced more valid results for shallow brain structures than other comparable algorithms. Finally, Mindboggle was shown to be reliable with minimal error estimate showing a consistently greater shape difference between left and right hemispheres than the difference between repeated scans of the same individuals.
Mindboggle also introduced many new and innovative features for extracting and measuring fundii but these algorithms have not yet been thoroughly evaluated. Additionally, the Mindboggle algorithms are developed for human brain anatomy and expansion into non-human neuroanatomy has not yet been fully developed. The potential of Mindboggle and similar platforms lies in the allowance to expand knowledge of normal human brain variation by using much larger samples to more accurately capture the normal range in human neuroanatomy to better inform diagnoses of brain abnormalities.
Recently Brazil has declared state of emergency due to an epidemic of newborn microcephaly. Children with microcephaly have significantly smaller head circumference than the mean for their age and body size. It results from abnormal brain development before birth or during infancy that can be caused by genetic (e.g. Down syndrome) or environmental factors affecting development, for instance craniosynostosis, malnutrition, and infection. Children with this condition may be cognitively impaired and need special medical care throughout their lives. During 2015 Brazil has been registering a drastic increase in the cases of microcephaly, mainly in the northeastern states. For instance in Pernambuco there was 141 cases while the mean is around 10 per year. Coincident with this epidemic, Brazil was also affected by a Zika virus outbreak firstly detected in late April and confirmed in 14 states by November. This virus was first identified in the 1940’s in Uganda, and it is now distributed throughout several tropical countries. It is transmitted to humans by bites of infected mosquitoes of the genus Aedes, the same that transmit dengue and yellow fever. Because symptoms of infection by Zika virus are mild it has not been given much attention. However the coincidence between the virus outbreak and increased microcephaly incidence in Brazil led to a suspicion that there was an association, further reinforced by the confirmation of the virus during an autopsy of a microcephalic baby.
The relationship between microcephaly and Zika virus is now being investigated and the government is taking steps to control the mosquitoes’ population and to assist the children with microcephaly. This virus may have spread from the French Polynesia, where there was an outbreak in 2013-2014, and where the Zika virus was associated with neurological complications like Guillain-Barré syndrome. If an association between a mosquito-transmitted virus and neurological conditions is confirmed, further measures of prevention must be taken as the area favorable for mosquitoes spreading seems to be increasing.
There are plenty of reports about anatomical and morphological variation of cranial foramina; however, their developmental mechanisms fundamental for interpretation of such a variation and understanding of vital medical conditions related to their aberrant formation are poorly known. Cranial foramina transmitting the vessels and nerves emerge within the cranial bones which themselves show complex origin and development. Recent embryological study in chicks by Akbareian et al. (2015) presents development of cranial foramina in mesoderm derived occipital bone arising through endochondral ossification. Unexpectedly, the formation mechanism did not show any extensive apoptotic cell activity and target proliferation. Instead as a “clearing” mechanism forming the cavity of foramina was proposed localized restriction of ossification caused by the presence of vessel and nerve elements with minimal mesenchymal cell death. Further importance for morphological studies of foramina can bear a discovery that the shape of vessel dictates the overall shape of the foramen.
Chiari Malformation type 1 (CM-I) is an anatomical hindbrain abnormality having various symptoms (headache, pain in the neck and shoulders) because of obstruction of cerebrospinal fluid circulation and compression of hindbrain tissues such as the cerebellum, brain stem and spinal nerve. Most CM-I have syringomyelia. There is no direct test for CM-I and often symptoms are misinterpreted. Indicating tests are MRI, CT, neurological tests and CINE PC MRI. Treatment is a surgical operation called “posterior fossa compression”. Recently, researchers from the Netherlands and Turkey conducted different studies to examine this disorder. Akar et al. tested the usefulness of fractal analysis to examine the morphological complexity features of CM-I. Fractal Dimension (FD) analysis conducts the structural differences between patients with MCI (n=17) and healthy control subjects (n=16). Results showed that patients with CMI have larger cerebellar gray matter (GM) areas compared to controls, in contrast to other studies. FD could be a significant indicator for brain abnormalities in the cerebellum of CMI. It seems to be the case that the higher the FD value of cerebellar , the more complex object structure was. Rijken et al. found by examining 28 not operated, 85 operated craniosynostosis patients and 34 control that development of CMI is more likely to be supra tentorial. Craniosynostosis patients with CMI have similar cerebellar volume (CV) and posterior fossa volume (PFV) to control subjects, but they do have a significantly higher CV/PFV ratio. A higher CV/PFV ratio can be regarded as a predisposing factor for the development of CMI. In the end Rijken et al. advise to focus more on the skull vault itself.
Johannes Freiherr von Boeselager
A recent study published by a large neuroscience team involved in imaging, cognition, and genetics, showed that cortical geometry is correlated with genetic ancestry. Using a sample of US citizens from the PING data, they reconstructed 3D cortical surfaces to obtain information on the morphological variation of the sulci and gyri. To calculate proportions of genetic ancestry they used as reference populations from west Africa, east Asia, a sample of native Americans and a sample of European descendants. The main finding of the study is that cortical folding patterns are strongly related to the genetic ancestry. According to the authors, African ancestry is associated with more posterior and narrower temporal areas. Frontal and occipital surfaces are more projected in Europeans and flatter in Native Americans. Asians have more variability in the temporal and parietal regions. Their results were similar to Howells’ craniometric analysis. Moreover, all but Europeans display increased morphological variation in the posterolateral-temporal region. Due to these morphological differences among populations, the authors warn for a possible methodological bias when mixing sample from different geographical origins in imaging studies.
The brain thermoregulation is an important issue from anthropology to medicine. The brain thermodynamic mechanisms in humans are still not well known and additional heat regulations in certain physiological and pathological conditions are crucial to prevent irreversible damages. Namely hyperthermia is a life-threatening condition causing severe functional alterations. The brain temperature can increase as a consequence of drug abuse, head injuries, strokes, etc. Releasing of the heat stress can be treated by plenty of invasive and non-invasive methods, systemic or selectively aimed. However, establishing new effective thermodynamic techniques to treat pathological conditions is still relevant issue. In craniotomies, the cooling method can consist of simple system of drainage tubes directly attached to the dural layers or brain passing a cooling liquid directly to the affected tissue. Such selectively aimed device can help the post-operative recovery and prevent possible complications. The principles of the device remotely reminds of radiator theory, possible thermoregulatory adaptation in human lineage ancestors proposed in paleoanthropology few decades ago.
I have previously published a post on the effects of space-travelling in astronauts, particularly concerning eyes and vision. This month, a group of researchers from the UC Irvine have published their study on the effects of space radiation in the brain and cognition. When travelling to Mars, astronauts are exposed to charged particles of the galactic cosmic rays, which can cause cell and tissue damage throughout the body. To find out the consequences of radiation in the brain, the team exposed mice to heavy ion irradiation and then examined their neuronal tissue and task performance. Their results revealed that these particles markedly and persistently change the structure of neurons and neurotransmission, leading to cognitive deficits. Furthermore, the intensity of damage correlates significantly with impairment in task performance, namely new object recognition and location. Thus, this work suggests exposition to space radiation can cause cognitive impairments which might be dangerous during the mission to Mars. Definitely, we are not adapted for the outer space. Yet.
Last Friday, March 27, NASA and Roscosmos sent two astronauts for a one-year space mission. The aim of this expedition is to investigate how being in space for such a long time can affect the human body and behaviour. Consequences of space flight environment in human physiology and psychology are already known, from common half-year missions. The point is to understand if these consequences are aggravated by a longer journey, as for a travel to Mars which would last about three years. According to the National Space Biomedical Research Institute, some of the body reactions to lack of gravity include loss of calcium in bones, loss of muscles mass (especially those used for posture), redistribution of fluids throughout the body, and changes in the balance system. Scientists are particularly interested in the effects of such environment in vision, since some astronauts have been reporting vision impairment, namely degradation of near vision, during and after space missions.
As a review by Marshall-Bowman and colleagues suggests, the causes of this vision deterioration are not yet fully understood, but they have been hypothesized to be based on the redistribution of body fluids. In a microgravity environment fluids are not pulled down by gravity and a greater amount is distributed in the upper body, including the head. Consequently, intracranial pressure increases, affecting the optic nerve, which swells due to difficult venous circulation. The eyeball becomes flatter, and shorter, leading to the hyperopic vision reported by the long-duration astronauts. However, the influence of other factors must be evaluated, like higher levels of carbon dioxide, the duration of the vision impairment after the space mission, and individual predisposition. This new expedition will be important to better understand these effects, also considering that one of the astronauts has a twin who will serve as a “Earth- control” to evaluate his brother’s body changes.
Studies in cranial morphology which consider at the same time soft and hard tissues are an indispensable source of information in medicine and evolutionary biology. Generally, medical studies use to provide rather descriptive analyses with direct relevance for, e.g. surgical treatment. However, combining different complementary approaches like computed tomography in living humans, microsurgery of cadavers, macroscopic inspection of dry skulls etc., we can supply quantitative data to understand normal and rare skeletal features, and assess the importance of specific traits in biological anthropology. A patent example is represented by the anatomical studies of blood vessels, analysing directly the vascular tissues but also their traces left on the cranial bones.
For instance, several types of intracranial orifice connections of posterior condylar emissary vein in the cranial base were recently identified. Following different course of condylar canal through which the vein is transferred through the bone it could be assessed with which venous structure the vein was interconnected. Additionally, the shifted location of the intracranial orifice can in specific cases indicate the presence of other venous structures as marginal sinus or occipital sinus which rarely leaves any visible routes in occipital bone although the actual prevalence in humans is high. Condylar canal belongs to skeletal nonmetric foraminal variants used as markers of phenotypic distances in various bioarchaeological targets. Traditionally, the major distinguishing value ascribed to nonmetric traits is their presence or absence; nevertheless, foramina express lower hereditary values in comparison with nonmetric traits of hyperostotic background. This could be explained by composite character of foraminal traits manifesting high variation in several aspects (e.g. number, branching patterns, ramification, bone position, size and length of orifices). Accordingly, it can be difficult to understand if and which specific morphological character can be used to evaluate biodistance discriminatory values. Medical and anatomical studies are essential in evidencing new unconsidered phenotypic variations which may become important in further bioarchaeological research, representing a promising way to improve our understanding of past populations.