The neural mechanisms underlying recovery of language after left hemisphere stroke remain elusive and are still debated after 130-years. Although older evidence suggested that right hemisphere language circuitry compensate for damage in the left hemisphere language areas, the current prevailing theory suggests that right hemisphere engagement is ineffective or even maladaptive. Now, a study from researchers at Georgetown University has shown that the loss of speech from a stroke in the left hemisphere of the brain can be recovered on the back, right-hand side of the brain. This team states that this contradicts recent notions that the right hemisphere interferes with recovery and while the findings may not put an immediate end to the century-old debate, they suggest a new direction in treatment.
Previous studies show that approximately one-third of stroke survivors lose speech and language, a disorder called aphasia, and most never fully regain it. The loss of speech occurs almost exclusively in patients with a left hemisphere stroke, with roughly 70% of people suffering stroke in this region facing language problems. Over the past decade, research has increasingly suggested that the right hemisphere interferes with good recovery of language after left hemisphere strokes. The current study suggests the opposite and shows that the right hemisphere actually compensates to improve recovery.
The current study performed neuroimaging on a group of 32 left-hemisphere stroke survivors via voxel-based morphometry to determine if increased grey matter volume in the right hemisphere related to better speech recovery. An additional 30 individuals were also enrolled who had not experienced a stroke as a control group. Results show that patients who regained their speech have increased grey matter volume in the back of their right hemisphere, mirroring the location of one of the two left hemisphere speech areas.
Data findings show that stroke participants who had better than expected speech abilities after their stroke had more grey matter in the back of the right hemisphere compared to stroke patients with worse speech. Results show that those areas of the right hemisphere were also larger in the stroke survivors than in the control group, indicating that growth in these brain areas relates to better speech production after a stroke. The lab state that to their knowledge this is the first study to look at brain structure and grey matter volume in relation to recovering speech after a stroke.
The team surmise that the speech centre identified aids only in the use of speech, and not in understanding what is said. For the future, the researchers will continue their study, looking for areas that compensate for other aspects of language use, such as comprehension of speech.