The Superpower of Left Brain-Right Brain Flexibility
Kids have more interhemispheric plasticity and recover from brain damage faster.
Posted Sep 09, 2020
For most neurologically healthy adults, language processing is considered a "left brain" function that relies on undamaged neural matter in the left cerebral hemisphere's Broca's area. However, for reasons that are still not wholly understood, in some healthy adults, language-related functions are seated primarily in the cerebral cortex's right hemisphere.
Interestingly, whereas 95 percent of right-handed adults tend to process language primarily in the left cerebral hemisphere, only about 75 percent of left-handers are "left-brain" language processors (Mazoyer et al., 2014). Adults who use both hemispheres (or primarily the right cerebral hemisphere) for language processing are categorized as having "atypical lateralization."
Last year, a study (François et al., 2019) of brain lateralization and language processing led by Clément François of Aix-Marseille Université in France reported that if a 4-year-old child had a stroke and suffered brain damage in the left hemisphere near the Broca's area, language functions could relocate to the "right brain." This fMRI study showed that interhemispheric plasticity makes it possible for brain functions to move from one hemisphere to another during early stages of development. (See "Study Shows Left Brain–Right Brain Reconfiguration in Action")
Now, another fMRI study (Olulade et al., 2020) by neuroscientists at Georgetown University Medical Center corroborates the interhemispheric flexibility of language development in young children. This paper, "The neural basis of language development: Changes in lateralization over age," was published on September 8 in Proceedings of the National Academy of Sciences.
"Infants and young children have brains with a superpower, of sorts," the Georgetown neuroscientists said in a news release.
For this study, first author Olumide Olulade and coauthors used fMRI neuroimaging to compare language activation maps for study participants in four age groups: 4 to 6, 7 to 9, 10 to 13, and 18 to 29. This research team was led by senior author Elissa Newport, neurology and rehabilitation medicine professor at GUMC and director of its Center for Brain Plasticity and Recovery.
Olulade et al. found that young children (4 to 6 years old) tend to use both cerebral hemispheres to process spoken sentences. However, by age 10 or 11, most language activation in an fMRI seemed to "light up" the left cerebral hemisphere's Broca's area. "These facts suggest that language is distributed to both hemispheres early in life; this is very good news for young children who experience a neural injury," Newport said in the news release.
Because lateralized language functions are not set in stone at a young age, if the left hemisphere is damaged by something like a perinatal stroke (which tends to occur just after someone is born), the right hemisphere has mechanisms in place to compensate for a neural injury in the left hemisphere, and vice versa. "A child born with cerebral palsy that damages only one hemisphere can develop needed cognitive abilities in the other hemisphere. Our study demonstrates how that is possible," Newport added.
Although brain plasticity is possible at any age, these findings help to explain why it is more difficult for adults to reconfigure lateralized brain functions and recover from neural injuries than it is for children. As we get older, left brain-right brain functions tend to become hardwired and "set in stone," which makes the brain less plastic and more difficult to "rewire."
According to the authors of the latest (2020) research on how language lateralization changes as people age, their study "solves a mystery that has puzzled clinicians and neuroscientists for a long time" related to language loss in adult patients who experience a stroke in their left cerebral hemisphere but not in children who suffer similar damage to their "left brain."
"Our findings suggest that the normal involvement of the right hemisphere in language processing during very early childhood may permit the maintenance and enhancement of right hemisphere development if the left hemisphere is injured," Newport concluded.
* fMRI Brain Activation Map (Image) via EurekAlert, no usage restrictions, with credit to Elissa Newport
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