The Brain's Ability to Rewire Itself Gives Kids a Superpower

Children's neuroplasticity can preserve functional connectivity in amazing ways.

Posted Oct 31, 2020

A growing body of MRI and fMRI evidence illustrates the developing brain's incredible ability to rewire itself via structural neuroplastic responses to trauma or congenital malformations.

Last year, researchers (François et al., 2019) from the Cognition and Brain Plasticity Group in Spain pinpointed how the right cerebral hemisphere could "take over" left-brain language functions in a cohort of 4-year-old children who had suffered a perinatal arterial ischemic stroke. This fMRI study shows left brain-right brain reconfiguration in action; it also illustrates how interhemispheric neuroplasticity can relocate brain functions from one cerebral hemisphere to another during infancy and the early stages of childhood development.

Last month, neuroscientists from Georgetown's Center for Brain Plasticity and Recovery in the U.S. published a paper with fMRI images showing how the interhemispheric flexibility of infant and young children's cerebral hemispheres makes it possible for language functions to become a "right-brain function" if language-specific areas in the left cerebral hemisphere are damaged. This study (Olulade et al., 2020) was published on September 8 in Proceedings of the National Academy of Sciences.

Life Science Databases/CC BY-SA 2.1 jp
Corpus callosum in red
Source: Life Science Databases/CC BY-SA 2.1 jp

Now, a new study (Siffredi et al., 2020) of children born without a corpus callosum connecting their left-right cerebral hemispheres shows how structural neuroplastic responses can preserve functional connectivity and how the brain can adapt to a rare congenital malformation in miraculous ways. These findings by Swiss neuroscientists from the Université de Genève (UNIGE), in collaboration with Australian colleagues at the University of Melbourne, were published on October 27 in the journal Cerebral Cortex.

 Unige/Siffredi, labeled for reuse
This side-by-side comparison shows neuronal fibers in a healthy brain (left) and a brain with agenesis of the corpus callosum (right). In the healthy brain (on the left), the two cerebral hemispheres are connected by the corpus callosum fibers, shown in red. These fibers are absent in the brain with corpus callosum agenesis (on the right).
Source: Unige/Siffredi, labeled for reuse

About one in 4,000 babies are born without the corpus callosum's interhemispheric white matter pathways; the absence of this bridge connecting the two cerebral hemispheres is called agenesis of the corpus callosum. Surprisingly, about a quarter of individuals born without a corpus callosum don't display any abnormal symptoms. 

As you can see in the MRI images above, when the white matter fibers that facilitate interhemispheric communication between the so-called "left brain-right brain" are missing, each hemisphere can independently reorganize itself by creating more robust intrahemispheric connections on each side. As the authors explain:

"For structural connectivity, children with agenesis of the corpus callosum showed a significant increase in intrahemispheric connectivity in addition to a significant decrease in interhemispheric connectivity compared with typically developing controls."

The researchers speculate that "these mechanisms enable the brain to compensate for the losses by recreating connections to other brain regions using alternative neural pathways."

"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," first author Vanessa Siffredi said in a news release.

"New connections are created, and the signals can be re-routed so that communication is preserved between the two hemispheres," Siffredi added. "If two regions are active together, it means they are communicating with each other."

For reasons that the neuroscientists don't completely understand, in some children with corpus callosum agenesis, structural neuroplastic responses within each hemisphere can preserve interhemispheric functional connectivity comparable to the left brain-right brain connectivity observed in typically developed, healthy controls. More research is needed to fully understand this phenomenon.

Unige/Siffredi image via EurekAlert

References

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

Olumide A. Olulade, Anna Seydell-Greenwald, Catherine E. Chambers, Peter E. Turkeltaub, Alexander W. Dromerick, Madison M. Berl, William D. Gaillard, and Elissa L. Newport. "The Neural Basis of Language Development: Changes in Lateralization Over Age." PNAS (First published: September 08, 2020) DOI: 10.1073/pnas.1905590117

Clément François, Pablo Ripollés, Laura Ferreri, Jordi Muchart, Joanna Sierpowska, Carme Fons, Jorgina Solé, Monica Rebollo, Robert J Zatorre, Alfredo Garcia-Alix, Laura Bosch, and Antoni Rodriguez-Fornells. "Right Structural and Functional Reorganization in 4-Year-Old Children with Perinatal Arterial Ischemic Stroke Predict Language Production." eNeuro (First published: August 05, 2019) DOI: 10.1523/ENEURO.0447-18.2019