A new study has discovered that major infant stroke to the left hemisphere of the brain, just days after birth, brains are ‘plastic’ enough for the right hemisphere to acquire the language abilities.
Language is normally handled by the left side, so the right side handles this as well as maintaining its own language abilities.
The left hemisphere of the brain is usually responsible for the understanding of sentences and words as we listen to speech, whilst the right hemisphere holds the responsibility of processing the emotion of the voice.
This study aims to answer the question of: “What happens when one of the hemispheres is injured at birth?”
In this study, from researchers at Georgetown University Medical Centre, participants developed normally during pregnancy.
However, around their time of birth they had a significant stroke, if an adult were to have a stroke of a similar kind it would leave them debilitated.
A stroke in infants is a very rare occurrence, happening in 1 in every 4,000 births.
Study Process & Findings
The researchers studied perinatal arterial ischemic stroke, a type of brain injury occurring around the time of birth in which blood flow is cut off to a part of the brain by a blood clot.
The same type of stroke occurs more commonly in adults.
First author of the study, Elissa Newport says: “Our most important conclusion is that plasticity in the brain, specifically the ability to reorganise language to the opposite side of the brain, is definitely possible early in life.
“However, this early plasticity for language is restricted to one brain region. The brain is not able to reorganise injured functions just anywhere as more dramatic reorganisation is not possible even in early life.
“This gives us great insights into the regions we might be able to focus on for potential breakthroughs in developing techniques for recovery in adults as well.”
The investigators recruited individuals across the United States who all had medium to large infant stroke to the cortex region go the left hemisphere around time of birth.
This was in order to assess long-term outcomes in their language abilities, participants were given language tests at 9 to 26 years of age and were compared to their close-in-age health siblings.
They were also scanned in an MRI to reveal which brain areas were involved in sentence comprehension.
The participants, along with their healthy siblings, completed the language tasks almost perfectly.
However, the major difference was that the infant stroke participants processed sentences on the right side of the brain, whilst their siblings processed sentences on the left side.
The stroke participants also showed a very consistent pattern of language activation in the right hemisphere, regardless of the extent or location damage from the stroke to the left hemisphere.
Only one of the 15 participants, who had the smallest infant stroke, did not display clear right hemisphere dominant activation.
Newport says: “It is also notable that many years after their strokes our participants are all such highly functioning adults. Some are honour students and others are working toward or have gotten their master’s degrees.
“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.”
In future studies, the researchers hope to gain an improved understanding of 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.
Another question of clinical importance, is why left hemisphere language can successfully reorganise to the right hemisphere if injuries occur very early in life, but not later?
Current research on stroke recovery and sentence processing in adults suggests that plasticity narrows with age.
