A new study in the journal Cerebral Cortex highlights the brain’s amazing capacity to rewire itself in order to avoid any loss of function when key structures are missing. In this case, the researchers focused on the corpus callosum, which bridges the two hemispheres of the brain yet fails to develop in around one in 4,000 people.
Those who are born with agenesis of the corpus callosum (AgCC) – meaning they suffer from the absence of this neuronal structure – can develop severe cognitive deficiencies, yet around a quarter of people with AgCC experience no symptoms whatsoever. To determine how a brain can continue to function normally with no corpus callosum, the study authors used functional magnetic resonance imaging (fMRI) to scan the brains of 49 children, 20 of whom had AgCC.
Unsurprisingly, the children that lacked a corpus callosum displayed a marked decrease in interhemispheric structural connectivity, meaning they had less white matter running between the two sides of their brain. However, this was offset by an increase in intrahemispheric structural connectivity, whereby the number of neuronal connections in each hemisphere was elevated, indicating a greater number of pathways on either side.
More incredibly, however, no differences in interhemispheric functional connectivity were observed between the two groups. In other words, brain regions in opposing hemispheres were able to communicate just as effectively in children with AgCC as those that possessed a corpus callosum.
The study authors say that the brain’s incredible plasticity is responsible for this, as the creation of extra connections and pathways allows for alternative routes of communication to arise between brain regions in opposite hemispheres.
“Remarkably, communication between the two hemispheres is maintained,” explained study author Vanessa Siffredi in a statement. “We think that plasticity mechanisms, such as the strengthening of structural bonds within each hemisphere, compensated for the lack of neuronal fibres between hemispheres. New connections are created and the signals can be re-routed so that communication is preserved between the two hemispheres.”
In both groups of children, interhemispheric functional connectivity was strongly correlated with cognitive abilities such as verbal learning and memory. In those with normal brains, this is directly linked to interhemispheric structural connectivity, or the amount of white matter in the corpus callosum. In children with AgCC, however, this is determined by intrahemispheric structural connectivity.
In other words, the more new connections that are formed within each hemisphere, the more communication is able to occur between the hemispheres, all of which lead to greater cognitive skills.
