Language Processing Can Flip from Left Brain to Right Brain

After a left-brain stroke, babies use right cerebral hemisphere for language.

Posted Feb 19, 2018

Elissa Newport/The Pediatric Stroke Research Project
These are individual scans of two healthy controls and two individuals with a left-hemisphere (LH) perinatal stroke. The orange/yellow activation shows the normal language areas of the left hemisphere in healthy individuals, as compared with the reorganized language areas in individuals with a left-hemisphere perinatal stroke.
Source: Elissa Newport/The Pediatric Stroke Research Project

Teenagers and young adults who suffered "perinatal" (around the time of birth) stroke damage to the left hemisphere of the cerebrum can reorganize lateralized brain functions. Years after the stroke, recent neuroimaging shows that they are successfully using the right hemisphere of their cerebrum (Latin for "brain") to process language. 

These findings were presented over the weekend by cognitive neuroscientist Elissa Newport in a lecture, “Developmental Plasticity and Language Reorganization After Pediatric Stroke,” at the American Association for the Advancement of Science (AAAS) Annual Meeting (Feb. 15-19, 2018) in Austin, Texas.

Notably, the fMRI neuroimages above clearly show that the brain areas used for language processing in the right cerebral hemisphere after an LH perinatal stroke mirror corresponding brain regions in the left hemisphere (orange/yellow areas in the two images under "controls") typically used for language processing.

How Common Are Perinatal Strokes? 

Approximately one in 4,000 babies has a perinatal stroke shortly before, during, or after being born. Having a perinatal stroke that damages the left hemisphere can disrupt language-processing areas typically seated in the "left brain." However, because the newborn brain is especially malleable and "plastic," these functions can flip to the "right brain" if necessary (as seen in the vivid brain images above.)

Wikipedia/Creative Commons
The entire "cranial globe" has four hemispheres. "Left brain-right brain" typically refers to the left and right cerebral hemispheres. There are also two (often overlooked) hemispheres in the cerebellum. These are referred to as the left and right cerebellar hemispheres. PLEASE NOTE: The left cerebral hemisphere controls voluntary muscle movement on the right side of the body; the right cerebellar hemisphere subconsciously controls fine-tuned muscle coordination on the right side of the body. (And vice versa in a criss-cross fashion.)
Source: Wikipedia/Creative Commons

The lead investigator of this study, Elissa Newport, is a professor of neurology at Georgetown University School of Medicine and director of The Pediatric Stroke Research Project at the Center for Brain Plasticity and Recovery (CBPR). One primary goal of this research project is to identify exactly how "plastic" brain structure and function is at various stages of life. 

For her ongoing research about the plasticity of brain function during infancy and beyond, Newport collaborates with a multi-disciplinary team of researchers at Johns Hopkins University, Children's National Medical Center, Children's Hospital of Philadelphia, and MedStar National Rehabilitation Network.

Neuroplasticity Can Reorganize "Left Brain-Right Brain" Lateralized Functions

The latest research project by Newport et al. began with the questions: “Which areas of the brain are capable of controlling language functions, and how well do they do this? If language is reorganized, what happens to other functions in that hemisphere?

Pixabay/Creative Commons
DEBUNKING NEUROMYTHS: The "left brain" is not always the seat of language function, and the "right brain" isn't necessarily the seat of visual-spatial functions.
Source: Pixabay/Creative Commons

To answer these questions, Newport and colleagues studied a dozen individuals (aged 12 to 25) who had suffered a left-brain perinatal stroke and currently used the right side of their cerebrum for most language function. This cohort was carefully chosen based on the type of brain damage and specific areas of injury to the left cerebral hemisphere.

Interestingly, the most significant outward sign of damage to LH was that some students walked with a limp and had learned to make their left hand dominant because the stroke had impaired right-hand function. Again, this is because the left cerebral hemisphere controls the right side of the body.

In a statement, Newport explained the significance of this study:

“These young brains were very plastic, meaning they could relocate language to a healthy area, it doesn't mean that new areas can be located willy-nilly on the right side. We believe there are very important constraints to where functions can be relocated. There are very specific regions that take over when part of the brain is injured, depending on the particular function. Each function, like language or spatial skills, has a particular region that can take over if its primary brain area is injured. This is a very important discovery that may have implications in the rehabilitation of adult stroke survivors."

Newport adds: "Imaging shows that children up to about age four can process language in both sides of their brains, and then the functions split up: the left side processes sentences and the right processes emotion in language."

Increasingly, there is growing evidence that different aspects of language (vocabulary, syntax, emotional context, etc.) are processed and generated using different systems throughout the entire brain. For more see, "Language Utilizes Ancient Brain Areas That Predate Humans."

References

Developmental Plasticity and Language Reorganization After Pediatric Stroke” presented by Elissa L. Newport at the American Association for the Advancement of Science Annual Meeting (Feb. 15-19, 2018) in Austin, Texas.

Seydell-Greenwald, Anna, Katrina Ferrara, Catherine E. Chambers, Elissa L. Newport, and Barbara Landau. "Bilateral Parietal Activations for Complex Visual-Spatial Functions: Evidence from a Visual-Spatial Construction Task." Neuropsychologia (Published online: October 4, 2017) DOI: 10.1016/j.neuropsychologia.2017.10.005

Phillip Hamrick, Jarrad Lum, Michael T. Ullman. “Child First Language and Adult Second Language Are Both Tied to General-Purpose Learning Systems” PNAS (Published online ahead of print: January 29, 2018) DOI: 10.1073/pnas.1713975115   

Tzourio-Mazoyer, Nathalie, Fabrice Crivello, Bernard Mazoyer. "Is the Planum Temporale Surface Area a Marker of Hemispheric or Regional Language Lateralization?" Brain Structure and Function (First published online: November 3, 2017) DOI: 10.1007/s00429-017-1551-7

Geschwind, Norman. "The Organization of Language and the Brain." Science (1970) DOI: 10.1126/science.170.3961.940

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