Differential capacity of left and right hemispheric areas for compensation of poststroke aphasia

TLDR

Previous neuroimaging studies have not resolved whether the dominant or subdominant hemisphere contributes to recovery from poststroke aphasia. This study examined the relationship between language performance and PET activation patterns in 23 right‑handed aphasic patients at 2 and 8 weeks poststroke. The authors classified patients by lesion site (frontal, subcortical, temporal) and, with 11 controls, measured task‑evoked cerebral blood flow changes in 14 eloquent and contralateral homotopic regions defined on coregistered MRI, applying Bonferroni‑corrected t‑tests. Recovery varied by lesion type: subcortical and frontal patients showed substantial improvement with initial right‑hemisphere activation that later returned to left STG, whereas temporal patients improved only in word comprehension and failed to reactivate left STG, indicating that right‑hemisphere compensation is limited and efficient language restoration requires preserved left temporal regions.

Abstract

As previous functional neuroimaging studies could not settle the controversy regarding the contribution of dominant and subdominant hemisphere to recovery from poststroke aphasia, language performance was related to H2(15)O-positron emission tomographic activation patterns in 23 right-handed aphasic patients 2 and 8 weeks after stroke. In patients classified according to the site of lesion (frontal, n = 7; subcortical, n = 9; temporal, n = 7) and in 11 control subjects, flow changes caused by a word repetition task were calculated in 14 regions representing eloquent and contralateral homotopic areas. These areas were defined on coregistered magnetic resonance imaging scans and tested for significance (Bonferroni corrected t test, alpha = 0.0036). At baseline, differences in test performance were only found between the subcortical and temporal group. The extent of recovery, however, differed and was reflected in the activation. The subcortical and frontal groups improved substantially; they activated the right inferior frontal gyrus and the right superior temporal gyrus (STG) at baseline and regained left STG activation at follow-up. The temporal group improved only in word comprehension; it activated the left Broca area and supplementary motor areas at baseline and the precentral gyrus bilaterally as well as the right STG at follow-up, but could not reactivate the left STG. These differential activation patterns suggest a hierarchy within the language-related network regarding effectiveness for improvement of aphasia; ie, right hemispheric areas contribute, if left hemispheric regions are destroyed. Efficient restoration of language is usually only achieved if left temporal areas are preserved and can be reintegrated into the functional network.