A stroke on the left side of the brain often affects speech and language.
The brain is divided into two hemispheres, the right and the left. In most people, the left side dominates in language and speech-motor functions. If the left side of the brain is damaged by stroke, aphasia can result.
Aphasia can cause problems with speaking, naming, repeating and understanding language.
Many people recover some of these faculties, but for many, even intense speech therapy does not lead to a full recovery.
Previous studies have shown that levels of injury to gray and white matter in structures in the left side of the brain can predict the potential for recovery
However, the role played by the right hemisphere in regaining speech-language functions has remained unclear.
Dr. Gottfried Schlaug, of Harvard Medical School in Boston, MA, and colleagues studied 33 people with aphasia following a stroke on the left side of the brain.
Speech recovery correlates with levels of structure within the brain
The average age of participants was 58 years, and they all had a stroke around 2.5 years prior to the current research. They had all undergone speech therapy.
In addition, 13 people of similar ages who had not had a stroke were included in the tests as a control group.
All the participants underwent speech fluency tests, and brains scans were carried out using a special magnetic resonance imaging (MRI) technique. The MRI enabled the researchers to examine tissue integrity and connectivity in various regions of the brain.
- Stroke kills 130,000 Americans every year
- 795,000 people have a stroke every year
- Around 87% of strokes are ischemic, meaning that blood flow to the brain is blocked.
The team hypothesized that where there was better structural integrity, better connections might also exist between different areas of the brain.
Results showed that patients with aphasia and better results in speech-fluency tests were more likely to have higher structural integrity than the control group in three areas of the brain.
The three areas were the right middle temporal gyrus, the right inferior frontal and the right precentral gyrus.
The correlation scores between the amount of injury to the left hemisphere and speech-fluency scores improved when the right hemisphere information was added to the analysis.
When researchers factored information from the right side of the brain into the statistical analysis, the amount of variance explained went from 50% to 62% for words per minute.
On this basis, researchers concluded that these right hemisphere regions contribute to speech fluency.
The study further suggests that the right side of the brain reorganizes itself after a stroke to help language/speech-motor functions recover.
It is possible that those who made a better recovery had better structural integrity and more connectivity in those right hemisphere areas of the brain before their strokes.
In a corresponding editorial, Dr. Anna M. Barrett, of the Kessler Foundation in West Orange, NJ, says:
"This study suggests that a well-wired right brain actively supports recovery from aphasia."
Dr. Barratt calls for further research to establish whether the differences in structural integrity in the right side of the brain exist before the stroke, develop after it or whether other factors influence it.
The findings could ultimately lead to new therapeutic targets in the right hemisphere and new treatments for aphasia - for example, brain stimulation.
Dr. Schlaug also suggests that melodic intonation therapy, focusing on the right side of the brain, could be another potential target. Melodic intonation therapy is an intonation-based therapy.
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