An infant’s brain can counteract loss of language after a stroke

An infant’s brain can bilaterally counteract loss of language after a stroke. A new study suggests that newborns who had a stroke in the left hemisphere of their brain were able to still learn language through their right hemisphere.

The brain of an infant is still considered ‘plastic’ enough for the right hemisphere to acquire language that would normally be handled by the left hemisphere. This means that it can be molded in a way that the brain can reorganize language in the hemispheric region not injured.

The study was published in Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Responsibilities of each brain hemisphere

The left hemisphere of the brain is usually responsible for comprehending sentences and words when listening to speech. The right hemisphere is responsible for processing emotions with the voice. However, the research wanted to see what would happen to the brain hemisphere if one side is injured at birth.

The research and breakthrough

In the study, the babies developed normally during pregnancy. However, around the time they were born, they suffered from a stroke. This perinatal stroke, or stroke in a newborn, was considered so significant that it would have the potential to cause debilitating outcomes as an adult. The participants were considered rare since stroke is considered less common in babies, although, according to the research, it does happen “in roughly one out of every four thousand births.”

The research team studied perinatal arterial ischemic stroke, a type of brain injury that occurs around the time of the baby’s birth. This injury cuts blood flow off to part of the brain, due to a blood clot. The stroke studied in the infants is more prevalent in adults.

Although previous studies of brain injuries in infants have been conducted, this one is unique because it focuses solely on a specific type of injury that allows the researchers to find consistency with prior work.

“Our most important conclusion is that plasticity in the brain, specifically the ability to reorganize language to the opposite side of the brain, is definitely possible early in life,” says Elissa Newport, Ph.D., first author of this study and director of the Center for Brain Plasticity and Recovery at Georgetown Medical Center.

However, the plasticity seems to only work within one region of the brain. Newport continues, “The brain is not able to reorganize injured functions just anywhere as more dramatic reorganization is not possible even in early life.”

The findings in this study potentially allow scientists to have insights on regions of the brain to focus on for future developmental recovery techniques, in both children and adults.

Participants recruited for the study

The research team studied people from across the U.S. who had medium to large strokes to the cortex region of their brains when they were born. To assess the long-term results in the effect on the participants’ language abilities, the researchers gave language tests to participants from nine to 26 years old, while comparing them to their similarly aged healthy siblings. The participants also were given an MRI to see which part of the brain were involved in understanding sentences.

The individuals in the study and their siblings completed all of the tasks superlatively, almost without any errors. However, the main difference revealed was that the stroke participants processed sentences in the right hemisphere of the brain while their siblings comprehended sentences on the left side. “The stroke participants showed a very consistent pattern of language activation in the right hemisphere, regardless of the extent or location of damage from the stroke to the left hemisphere,” the study said.

Researchers also noted that only one of the 15 individuals with the previous perinatal stroke didn’t show dominance in language activation in the right hemisphere of the brain. This one participant also had the smallest stroke in the study.

The study also showed that the participants were high functioning adults with exemplary achievements, despite having the strokes as babies. “It is also notable that many years after their strokes our participants are all such highly functioning adults,” Newport said. “Their achievements are remarkable, especially since some of their parents had been told when they were born that their strokes would produce life-long impairments.”

Hemispheric dominance

The study sheds light on the function of the brain and what occurs when infants have a stroke, following them all the way through adulthood. However, the research also leads to more questions, such as “why the left hemisphere routinely becomes dominant in healthy brains but consistently loses out to the right hemisphere when there is a significant left-hemisphere stroke.” Researchers also want to look further into why the left hemisphere can reorganize language to the right hemisphere of the brain if injuries occur early in life, but not when the child is older.

Researchers want to use the information gained from this study to help adult stroke survivors heal and recover.