When Stroke Harms One Side of a Newborn's Brain, Other Side Takes Over
Many language skills are "left brain," but a new study shows that when a newborn suffers a stroke in that region, the brain is able to shift those language duties to the right.
The researchers said the findings highlight the striking malleability of the infant brain, and could potentially point to ways to treat adults who suffer similar strokes.
Strokes occur when the blood supply to part of the brain is cut off, starving the tissue there. Depending on the location and extent of the damage, strokes can leave people with physical disabilities or problems with memory, thinking or communication.
While older adults account for most strokes, they can strike younger adults, kids and even babies.
Perinatal strokes — those that occur around the time of birth — affect roughly one in every 4,000 newborns, according to the International Alliance for Pediatric Stroke.
The new study, published Oct. 10 in the Proceedings of the National Academy of Sciences, included 15 teenagers and young adults who'd suffered a perinatal arterial ischemic stroke. That's the most common type of perinatal stroke, and it occurs when an artery in the brain is blocked by a blood clot.
In these cases, the stroke had damaged the language-governing areas in the left hemisphere of the brain.
Despite that, all 15 young people had normal scores on tests of language skills — including the ability to process spoken words and sentences and to interpret vocal emotions.
Specialized MRI scans revealed how that was possible: Their brains had moved the responsibility for all language skills to specific areas in the right hemisphere of the brain. The "right brain" normally handles the vocal-emotion piece, but not word processing.
The results demonstrate the remarkable "plasticity" of the brain in early life, said lead researcher Elissa Newport, a professor of neurology at Georgetown University Medical Center, in Washington, D.C.
It's been known that people who suffered such strokes as a newborn can go on to have typical language skills. But it's important to understand what is happening in the brain to allow that, according to Newport.
That knowledge could prove useful in developing treatments for strokes that happen later in life, she noted.
Researchers have had different ideas on how language abilities are recovered after perinatal stroke. One is that uninjured parts of the left hemisphere take over; another is that the newborn brain is so malleable, that language duties can be assumed by areas that normally have nothing to do with language.
A third hypothesis, Newport said, holds that left-brain language skills are transferred to a specific part of the right hemisphere — the frontotemporal cortex, which normally takes care of interpreting the emotional part of communication.
That's what Newport's team saw in their study participants.
Their language recovery is remarkable, Newport said, since their left-hemisphere injuries would have devastated communication skills in an adult.
"We think they do so well because in young children, the brain is not so lateralized," Newport said. That is, the brain's various jobs are not as fixed to one hemisphere, as is the case in adults.
According to Dr. Solomon Moshé, a neurologist and professor at Montefiore Medical Center/Albert Einstein College of Medicine, in New York City, "The developing brain does have the ability to compensate for very serious injury."
Moshé, who was not involved in the new study, said, "We've seen babies recover from injuries that adults cannot tolerate."
He said the message from these findings for parents is, "Be optimistic." If a newborn suffers this type of stroke there is still a good chance for normal language development, Moshé added.
Newport said that while older brains are not innately capable of such plasticity, one question is whether they can be encouraged in that direction. Could, for instance, noninvasive stimulation of right-hemisphere structures, along with standard speech therapy, help stroke survivors with language impairments?
Of course, a large stroke to the left hemisphere can affect functions beyond language. And not all can be recovered, Moshé noted.
The 15 young people in this study did have some lasting effects from their early-life stroke — including paralysis of the right hand, and mild problems with short-term memory and information-processing speed.
But overall, they were thriving, Newport said, with many working toward or having higher-education degrees.
For more about stroke in newborns, visit the International Alliance for Pediatric Stroke.
SOURCES: Elissa Newport, PhD, professor, neurology, director, Center for Brain Plasticity and Recovery, Georgetown University Medical Center, Washington, D.C.; Solomon L. Moshé, MD, chair, neurosurgery and neurology, Montefiore Medical Center, professor, neurology, neuroscience & pediatrics, Albert Einstein College of Medicine, Bronx, N.Y.; Proceedings of the National Academy of Sciences, Oct. 10, 2022, online