Neurobiologists at Tomsk State University (TSU) study congenital brain abnormalities during the human prenatal and postnatal periods. By studying agenesis of the corpus callosum (total or partial absence of the structure that connects the two hemispheres of the brain), scientists have found that its functions can be compensated by other brain structures. The cognitive capacities of the child remain intact. These new data can radically change clinical practice and reduce the number of terminations of pregnancy. The project is supported by the Russian Science Foundation.
The scientists used myelin mapping technology, a unique non-invasive technology created by neurobiologists at TSU. Myelin is a substance that surrounds the axons of nerve cells, and its quantity is an important criterion in assessing the brain development of a child or fetus. Scientists from TSU and specialists from the International Tomography Center, Siberian branch of the Russian Academy of Sciences (ITC SB RAS, Novosibirsk) study the early stages of myelin formation during prenatal development.
We chose the corpus callosum for this study because abnormalities in its development are frequent â, explains Aleksandra Korostyshevskaya, Principal Investigator, Head of the Department of Medical Diagnosis at ITC SB RAS, Doctor of Medical Sciences. âAnomalies of mid-brain structures account for 47% of all pathologies of brain development, and among them 40% are related to underdevelopment (agenesis) of the corpus callosum. It’s hard to say what life has in store for these children. Doctors and parents are faced with a difficult choice: to risk giving birth to a child with an intellectual disability or to terminate a pregnancy. “
It is not always possible to detect the details of the abnormality with prenatal ultrasound. In almost half of cases, an MRI of the fetus is needed to determine agenesis of the corpus callosum. However, this is complicated because the fetus is constantly moving through the amniotic fluid. ITC SB RAS specialists were among the first to introduce this diagnostic method in 2008, and have been perfecting it for over 13 years.
In collaboration with TSU, scientists at ITB SB RAS have developed a new step in global practice: a method for quantitatively mapping myelin in the brain of a fetus.
“We assembled a representative sample of fetuses with agenesis of the corpus callosum,” says Vasily Yarnykh, research advisor at the Research Institute of Biology and Biophysics, TSU, and professor at TSU and the University of Washington. “We compared them to a sample without abnormalities and found that myelin in central brain structures is formed more quickly in children without corpus callosum. This means that the absence or partial absence of a brain structure is compensated for. by others, and they connect two hemispheres instead of the corpus callosum. “
This evidence for neuroplasticity in the human brain explains why people with corpus callosum agenesis can function well in the absence of other abnormalities. During examinations, clinicians encountered patients between the ages of 50 and 70 without corpus callosum. They lead normal lives and are well integrated into society. At the time of their birth, MRI and ultrasound were not available and the parents were unaware of the abnormality of their children. These people’s brains compensated for the absence of a corpus callosum by “activating” other parts. To understand the mechanism of neuroplasticity, scientists need to determine which structures can perform the functions of other parts.
“We are studying fetuses at this stage of development where myelin is only just starting to form,” says Vasily Yarnykh. âOn the maps of myelin, we can see that with agenesis of the corpus callosum, myelin forms more quickly in the marrow and spreads to the cerebellum. It is likely that the structures of the hindbrain connect the hemispheres in l corpus callosum. Previously, it was considered that in this case, the functions of the corpus callosum are performed by other areas that form myelin after childbirth. Our fundamental finding alters our understanding of the interactions of the corpus callosum. brain structures.
New quantitative evidence from TSU and ITC SB RAS may alter existing clinical practice and provide a chance for life for children previously promised intellectual limitations and social maladjustment.
“Agenesis of the corpus callosum was previously considered a fatal defect, and if it was discovered before the 21st-23rd week, the pregnancy could be terminated,” says Aleksandra Korostyshevskaya. âIt is evident now that if the corpus callosum is absent, we need to check for accompanying diseases: central neural system pathologies and genetic syndromes. If everything is in order, the fetus has a chance to develop normally. Of course, we need more on a large scale. studies, but even the data we have now has radically changed the approach to corpus callosum agenesis. “
In early 2022, the scientists will present the results of their studies orally at the International Congress of Pediatric Radiology of the American Society of Pediatric Neuroradiology.
Malformation illustrates brain’s incredible plasticity
Provided by Tomsk State University
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