A Major Malformation Illustrates the Incredible Plasticity of the Human Brain

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Brain Neuronal Fibers

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Neuronal fibers in a healthy brain (top) and a brain with agenesis of the corpus callosum (bottom). In the healthy brain, the 2 hemispheres are linked by the corpus callosum fibers, displayed in red. These fibers are missing in the brain with corpus callosum agenesis. Credit: Unige/Siffredi

People born without a corpus callosum do not have a bridge in between the 2 cerebral hemispheres. Neuroscientists from UNIGE have actually demonstrated how the brain handles to adjust.

One in 4,000 individuals is born without a corpus callosum, a brain structure including neural fibers that are utilized to move info from one hemisphere to the other. A quarter of these people do not have any signs, while the rest either have low intelligence ratios or struggle with serious cognitive conditions. In a research study released in the journal Cerebral Cortex, neuroscientists from the University of Geneva (UNIGE) found that when the neuronal fibers that function as a bridge in between the hemispheres are missing out on, the brain rearranges itself and develops an outstanding variety of connections inside each hemisphere. These develop more intra-hemispheric connections than in a healthy brain, showing that plasticity systems are included. It is believed that these systems allow the brain to make up for the losses by recreating connections to other brain areas utilizing alternative neural paths.

The corpus callosum establishes in utero in between the tenth and twentieth week of pregnancy. Agenesis of the corpus callosum is a hereditary brain malformation in which this brain structure stops working to establish, leading to one out of 4,000 infants born without a corpus callosum. When it is missing out on, absolutely nothing changes this structure determining about 10 centimeters, with the exception of cerebrospinal fluid. This indicates that the info transferred from one hemisphere to the other can no longer be communicated by the neuronal forecasts from the corpus callosum. “Their role in a healthy brain,” starts Vanessa Siffredi, a scientist in UNIGE’s Faculty of Medicine, “is to ensure the functioning of various cognitive and sensorimotor functions.” Surprisingly, 25% of individuals with this malformation have no noticeable indications; 50% have typical intelligence ratios and finding out problems; and the staying 25% struggle with serious cognitive conditions. 

Mysterious fibers

The clinical literature reveals that, in the lack of the corpus callosum, particular fibers developed to function as a bridge in between the hemispheres, referred to as Probst packages, bypass the missing brain location and huddle inside each hemisphere. “The back-up zones vary from one individual to another. And we don’t understand their functions,” describes the neuroscientist. The UNIGE researchers – operating in partnership with their coworkers at the University of Melbourne – set out to comprehend this irregularity and to take a look at the function of the fibers. Using MRI brain imaging, they studied the physiological and practical links in between various brain areas of roughly 20 Australian kids aged 8 to 17 struggling with agenesis of the corpus callosum. 

A salutary function

This method initially made it possible to observe the physical relationships in between the various areas of the brain, i.e. their structural links. In kids with corpus callosum agenesis, the neural fibers inside each hemisphere are higher in number and of greater quality than in healthy brains. Furthermore, the UNIGE researchers prospered in identifying the connections in between the activity of various brain areas and their practical links. “If two regions are active together, it means they are communicating with each other,” describes Dr. Siffredi. The information reveals that intra- and inter-hemispheric practical connection of brains without the corpus callosum are similar to those of healthy brains. “Remarkably, communication between the two hemispheres is maintained. We think that plasticity mechanisms, such as the strengthening of structural bonds within each hemisphere, compensated for the lack of neuronal fibers between hemispheres. New connections are created and the signals can be re-routed so that communication is preserved between the two hemispheres.”

Predicting cognitive problems

The Geneva neuroscientists also observed a connection in between the boost in intra-hemispheric connections and cognitive abilities. This info is really fascinating for scientific work considering that, as agenesis is presently discovered by ways of ultrasound throughout pregnancy, it is typically proposed that a pregnancy be ended. “In the not-too-distant future, we could imagine using MRI imaging to predict whether the malformation observed by ultrasound runs the risk of being associated with cognitive impairment or not, and so better inform future parents,” concludes Dr. Siffredi.

Reference: “Structural Neuroplastic Responses Preserve Functional Connectivity and Neurobehavioural Outcomes in Children Born Without Corpus Callosum” by Vanessa Siffredi, Maria G Preti, Valeria Kebets, Silvia Obertino, Richard J Leventer, Alissandra McIlroy, Amanda G Wood, Vicki Anderson, Megan M Spencer-Smith and Dimitri Van De Ville, 27 October 2020, Cerebral Cortex.
DOI: 10.1093/cercor/bhaa289