Stroke is a leading cause of disability in the US, with loss of speech being one of its many devastating effects. For years, some scientists have claimed the right hemisphere of the brain interferes with speech recovery following stroke in the left hemisphere; but according to a new study, the opposite is true.
Publishing in the journal Brain, researchers from Georgetown University Medical Center (GUMC) in Washington, DC, found that the right side of the brain increases growth of gray matter to compensate for loss of gray matter in speech-related areas in the left side due to stroke, which can aid speech recovery.
Study coauthor Dr. Peter Turkeltaub, assistant professor of neurology at GUMC, and colleagues say their findings may offer new treatment options for stroke.
Each year, more than 795,000 people in the US have a stroke. Of these, around 185,000 are first-time strokes.
The effects of stroke depend on how much brain tissue is affected and in what part of the brain it occurs. For example, if stroke occurs in the right side of the brain, this may lead to problems such as vision loss and paralysis on the left side of the body.
If stroke occurs in the left side of the brain, this may lead to paralysis on the right side of the body and speech and language problems. Around a third of people who survive a stroke experience loss of speech, known as aphasia, and this almost always occurs in those who have experienced left-hemisphere strokes; around 70% of left-hemisphere stroke survivors have language problems.
Some individuals who experience speech loss after stroke may recover gradually in subsequent months, although most never fully recover. Over the past decade, studies have suggested the right side of the brain impairs the speech recovery process; the GUMC team set out to investigate this theory further.
The researchers enrolled 32 individuals with aphasia who had experienced stroke in the left hemisphere of the brain, alongside 30 people who had not had a stroke.
The stroke survivors underwent language assessments to determine severity of their speech problems, and all participants underwent high-resolution brain imaging to assess brain structure and volume.
Compared with stroke survivors who had poorer speech abilities, those with better-than-expected speech abilities had larger gray matter volumes in the back of the right hemisphere of the brain – an area that mirrors one of the two speech locations in the left hemisphere.
What is more, the researchers found that stroke survivors with better-than-expected speech abilities also had larger gray matter volume in the right hemisphere of the brain than control participants.
According to the investigators, these findings indicate that growth of gray matter in the right hemisphere of the brain compensates for loss of gray matter in the left hemisphere to improve speech.
Dr. Turkeltaub adds:
“Over the past decade, researchers have increasingly suggested that the right hemisphere interferes with good recovery of language after left hemisphere strokes. Our results suggest the opposite – that right hemisphere compensation improves recovery.”
The team notes that the area in the right hemisphere of the brain they identified only aids in use of speech, not understanding of speech. As such, the team plans to conduct further research to determine whether there are other areas of the right hemisphere that may compensate for speech comprehension.
The researchers hope their findings pave the way to new treatments for individuals who experience loss of speech after stroke.
Medical News Today recently reported on a study in which researchers discovered it may be possible to encourage self-repair of brain tissue following stroke.