When the bridge between the cerebral hemispheres is missing, the brain reorganizes

The corpus callosum adapts through reorganization to people born without a corpus callosum that does not have a bridge between the two hemispheres. These mechanisms are thought to allow the brain to compensate for loss by recreating connections to other brain regions using alternative neural pathways.

In the absence of nerve fibers that act as a bridge between the cerebral hemispheres, brain reorganization creates an impressive number of connections within each cerebral hemisphere. New studies show that this rearrangement creates connections within the cerebral hemisphere rather than a healthy brain, indicating that a plastic mechanism is involved. These mechanisms are thought to allow the brain to compensate for loss by recreating connections to other brain regions using alternative neural pathways.

This work is published in Cerebral cortex In the dissertation, “Structural neuroplastic response maintains functional connectivity and neurobehavioral outcomes in children born without corpus callosum.. “

One in 4,000 is born without the corpus callosum, a brain structure that transfers information from one hemisphere to another. The corpus callosum, which occurs in the uterus between the 10th and 20th weeks of gestation, is the largest white matter pathway in the brain that connects the two hemispheres.

If the corpus callosum is missing, there is nothing to replace the structure, except for cerebrospinal fluid. This means that the information sent from one hemisphere to the other hemisphere can no longer be transmitted by the projection of neurons from the corpus callosum.

Surprisingly, 25% of people with this malformation have no visible signs, 50% have average IQ and learning disabilities, and the remaining 25% suffer from severe cognitive impairment. I will.

“Their role in a healthy brain is to ensure a variety of cognitive and sensorimotor functions,” said Dr. Vanessa Sifredi, a researcher at UNIGE School of Medicine.

In the absence of the corpus callosum, certain fibers designed to act as bridges between hemispheres, known as Probst Bundles, bypass non-existent brain regions and round inside each hemisphere. “Backup zones vary from person to person, and we don’t understand their capabilities,” Sifredo explained.

UNIGE scientists have worked with colleagues at the University of Melbourne to try to understand this variability and investigate the role of fibers. Their hypothesis was that developmental deficiency of the corpus callosum (angenesis of the corpus callosum) could lead to a neuroplastic response that strengthens the intrahemispheric pathway.

Using MRI brain imaging, they usually develop anatomical and functional associations between about 20 different brain regions of about 20 Australian children aged 8 to 17 years suffering from agenesis of the cortex. I studied in comparison with (n = 29).

This approach has made it possible to observe the physical relationships between different regions of the brain, the structural links between them. Children with agenesis of the corpus callosum have a higher number of nerve fibers in each hemisphere and are of higher quality than a healthy brain. In addition, UNIGE scientists have succeeded in determining the correlation between activity in various brain regions and their functional links.

“If the two regions are working together, that means they are communicating with each other,” explained Sifredi. The data show that the functional connectivity within and between the hemispheres of the corpus callosum-less brain is comparable to that of a healthy brain. “Surprisingly, communication between the two hemispheres is maintained. We believe that plasticity mechanisms, such as strengthening structural connections within each hemisphere, compensated for the lack of nerve fibers between the hemispheres. A new connection can be created and the signal can be rerouted to maintain communication between the two hemispheres. “

The team not only observed structural enhancement of the intracerebral hemisphere pathways in children born without the corpus callosum, but also observed an increase in connections within the cerebral hemisphere and a correlation with cognitive skills.

This information is relevant for clinical research, as hypoplasia is currently detected by ultrasound during pregnancy and can accommodate abortion proposals. “In the not too distant future, we could imagine using MRI imaging to predict whether ultrasound-observed malformations are at risk associated with cognitive impairment, so we can provide better information to future parents. “I will.” Sifredo concludes.