In a new study, researchers observed young people who had left-brain stroke damage at birth and found they are now using the right side of the brain for language — in the exact, mirror-opposite region to the normal language areas on the left side.
At least one in 4,000 newborn babies experience a perinatal stroke, one that occurs right around the time of birth. But a stroke in a baby, even a big one, does not have the same long-term effects as an adult stroke. The findings help demonstrate just how “plastic” brain function is in infants.
For the study, researchers at Georgetown University Medical Center observed 12 individuals (aged 12 to 25) who had experienced a left-brain perinatal stroke, and found that all used the right side of their brains for language.
“Their language is good — normal,” said cognitive neuroscientist Elissa L. Newport, Ph.D., professor of neurology at Georgetown University School of Medicine, and director of the Center for Brain Plasticity and Recovery at Georgetown University and MedStar National Rehabilitation Network.
Some of the participants have a slight limp, and many have a dominant left hand because the stroke caused an impairment in right-hand function. They also have some executive function impairments — slightly slower neural processing, for example — that are common in individuals with brain injuries.
But basic cognitive functions, such as language comprehension and production, are excellent, Newport said.
Significantly, imaging studies show that the participants’ language function is based in the right side of the brain in the mirror-opposite region to the left normal language areas. This has also been found in previous studies, but earlier findings have been inconsistent, perhaps due to the heterogeneity of the types of brain injuries involved in those studies, Newport said.
The new study was carefully controlled in terms of the types and areas of injury included, and suggests that while “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,” saidNewport.
“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.”
This finding makes sense in very young brains, Newport noted. “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.”
The research team is extending the study to a larger group of participants, and is looking at both left and right brain strokes and also at whether brain functions other than language are relocated and where.
They are also collaborating on studies that may reveal the molecular basis of plasticity in young brains; information that might help switch on plasticity in adults who have suffered stroke or brain injury.
The findings were recently reported in a symposium at the American Association for the Advancement of Science (AAAS) Annual Meeting in Austin, Texas.