By Lucy Piper
White matter integrity in the right hemisphere may help to predict speech fluency recovery following a stroke, research indicates.
The results show that post-stroke patients with aphasia who performed better on speech fluency tests were more likely to have higher structural integrity in the right middle temporal gyrus, the pars opercularis of the right inferior frontal gyrus and the right precentral gyrus.
"Our findings indicate that right hemisphere white matter regions must play a role in speech-motor and language recovery, whether due to prestroke anatomical variability providing a favorable condition for recovery from left hemisphere lesions or due to poststroke remodeling", say Gottfried Schlaug (Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA) and co-researchers.
The team used fractional anisotropy (FA) to assess white matter integrity in 33 patients aged an average of 58 years who had suffered a stroke to the left side on average 2.5 years earlier. Despite speech therapy, all the patients had speech fluency impairment that progressed to varying degrees of aphasia.
FA values for the right middle temporal gyrus, the precentral gyrus and the pars opercularis of the inferior frontal gyrus significantly predicted outcomes on the speech fluency measures correct information units (CIU)/min (speech efficiency) and words/min (speech fluency).
Multiple regression analysis showed that adding the combined FA values for these right white matter regions to an existing strong predictor of speech fluency - lesion load of the left arcuate fasciculus - provided the best predictive model. This model explained 71% of variance in CIU/min and 62% of variance in words/min, compared with a respective 66% and 50% with lesion load of the left arcuate fasciculus alone.
The researchers compared FA values for these right white matter regions with those of 13 healthy individuals who had not suffered a stroke and found patients had significantly higher values for the precentral gyrus and the pars opercularis of the inferior frontal gyrus, but, surprisingly, not for the middle temporal gyrus.
"This may suggest that premorbid differences in [white matter] integrity of the right [middle temporal gyrus] or differential language lateralization contributed to recovery of speech fluency", they suggest in Neurology.
Differences in the precentral gyrus and pars opercularis of the inferior frontal gyrus are likely to be due to poststroke reorganisation, they add.
"This interpretation would suggest right hemisphere remodeling as a beneficial mechanism rather than a maladaptive one or an epiphenomenon, which is in contrast with interpretation of some previous studies", says the team.
FA values for corpus callosum fibres connecting left and right supplementary motor areas were also predictive of speech recovery and these values along with those for the whole corpus callosum were significantly lower in patients compared with controls, although only those for the whole corpus callosum survived Bonferroni correction.
The researchers suggest that axonal loss and demyelination associated with Wallerian degeneration caused by the left hemisphere lesion may explain these corpus callosum findings, particularly as they found FA values for the corpus callosum decreased in line with increasing damage to the left hemisphere.
Anna Barrett (Kessler Foundation, West Orange, New Jersey, USA) and Roy Hamilton (University of Pennsylvania, Philadelphia, USA) comment on the clinical importance of the findings in a related editorial.
"[E]xamining the right brain may eventually assist us in counselling patients and their families about the possibility of speech and language recovery", they say, adding that the positive influence of right hemispheric structures on aphasia may also offer "new treatment targets for novel interventions, such as brain stimulation, which can focally modulate and facilitate activity in the brain."
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