The Internet Brain Volume Database (IBVD) is an online collection of neuroimaging data funded as a part of the international initiative, the Human Brain Project. The IBVD provides access data for both individual and among-group comparisons that allow total volume comparisons with parallelization of the brain into hemispheres, specific lobes or grey matter volumes. While the database contains data on humans, there is also non-human primate (macaque) and rat studies. A summary search provides information on sex, age and handedness as well as age-related pathology, neuro-psychiatric disease, structural disease and twin-studies (monozygotic and dizygotic). These selected individuals can be compared to normal studies or pooled into user-specified group results. For example, it is very easy to generate a plot of left vs. right temporal lobe volume compared to age in normal human in vivo males and females.
The mature primate brain consists of many layers with the outer layer or cerebral cortex forming folds known as sulci and gyri. During embryonic development, the brain is divided into zones with the inner-most ventricular zone where neurons are formed and a series of cytoarchitecturally distinct layers forming plates radiating outward. The subplate is located between the inner ventricular zone and the outer cortical plate hosting the migration of neurons allowing brain expansion. Most embryonic brain research is conducted on non-primate mammals but there are substantial differences in the development of the non-primate and primate brain. A very recent study utilized existing primate tissue databases to examine the embryonic development of the subplate zone in non-human and human primates. Duque et al. found during that development of the macaque brain, once the neurons have migrated to the subplate they then are pushed downward by axons derived from the subcortical layer before further compression occurs from further axonal development originating from the cortical layer. The implications of this force acting on the neurons within the subplate suggests that thickness of the subplate differs unevenly throughout the brain potentially due to an increased axonal density. Duque et al. suggest the density of axonal fibers increases with demand for more connectivity between brain regions with those areas possessing a high-demand for greater complexity causing a thicker subplate.
Changes at the cellular-level of the subplate also have implications for the development of the cerebral convolutions such as sulci and gyri. It was recently posed that the folding patterns in the human brain are the result of mechanical forces related to the subplate and outer expansion of the cerebral cortex. Tallinen et al. showed through numeric and physical simulations with the support of MRI that during fetal development the subplate stabilizes while the outer cortical plate continues to expand. The final stages of growth see the cortical layer undergo extensive gyrification to form the folding patterns we see in the adult human brain. Overall, a better understanding of human neurobiology informed through non-human primate neurobiology offers a glimpse into the evolutionary pathways which led to the evolution of modern humans.
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.
Age-related cranial morphological changes in adult humans are generally considered as minor or negligible. However, with age the adult human cranium undergoes non-pathological processes of thickening. In the case of hyperostosis frontalis interna, for example, thickening preferentially involves the inner part of frontal bones, influencing the cranial morphology. Recently, a geometric morphometric study of recent human crania also revealed age related cranial shape changes. The shape differences in males and females ranging between 20-99 years can be mainly detected in the cranial vault and at the anterior and middle cranial fossa. In contrast, no changes were found in the posterior cranial fossa. In the vault, there are corresponding morphological changes on the outer and inner surfaces. The authors suggest that some shape modifications can reflect the increase of grey matter volume in early age groups (up to 30 years), and its loss in older age groups. Hence, such age-dependent changes are supposed to be secondary consequences of the relationship between cranial morphology and brain volume. Males generally showed more marked differences. Nevertheless, the small sample size for each age group makes this study preliminary.
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.
In their last review Jean-Jacques Hublin, Simon Neubauer and Philipp Gunz address the effects of hominins’ life histories in brain evolution. Encephalization in humans involved energetic costs that were sustained through changes in social structure and metabolic adaptations, including changes in the diet quality, as explained by the Expensive Tissue Hypothesis, and the ability to store energy in fat tissue, the primary source of energy for neonate brains. Because of the constraints of birth-giving associated with bipedalism, human brains develop mainly after birth. Also because of this prolonged development, the brain is exposed to a rich environment during its wiring process, with the child furthermore protected by the social community.
The study of fossil hominins’ brain development is only possible through the analysis of their endocranial casts, using cross-sectional samples. To establish their life histories it is necessary to attribute an age at death, generally according to the eruption timing of the teeth. Beyond variation in brain size, signs of brain reorganization can be investigated in fossil species to get insights about their cognitive capacities. Regarding Australopithecus, it is not yet clear how their brain development and life histories were more like that of humans or that of chimps. Homo erectus had body proportions and social structures closer to that of modern humans, but different brain organization and smaller brain capacity than that of latter Homo, pointing to a faster life history. Homo sapiens and H. neanderthalensis separately evolved similar brain capacities, although with different morphologies, and had different life histories, faster in the latter. Brain organization differs soon after birth, as modern humans undergo the so-called globularization phase, which does not exist in chimps or Neanderthals. This globular shape of the brain is characterized by the bulging of the parietal areas which may be linked to reorganization of the internal regions, like the precuneus.
There is still a debate about whether or not life histories in fossils can be investigated in terms of brain growth and development. The different brain morphology of Australopithecus when compared with African apes suggests that brain reorganization could have pre-dated encephalization. At last, our patterns of socio-cultural evolution might have been fundamentally responsible for the adaptive changes essential for the evolution of our big brains.