Recovered vs. not-recovered from post-stroke aphasia: the contributions from the dominant and non-dominant hemispheres

Abstract

Purpose: Several adult studies have documented the importance of the peri-stroke areas to aphasia recovery. But, studies examining the differences in patterns of cortical participation in language comprehension in patients who have (LMCA-R) or have not recovered (LMCA-NR) from left middle cerebral artery infarction have not been performed up to date.

Methods: In this study, we compare cortical correlates of language comprehension using fMRI and semantic decision/tone decision task in 9 LMCA-R and 18 LMCA-NR patients matched at the time of stroke for age and handedness. We examine the cortical correlates of language performance by correlating intra- and extra-scanner measures of linguistic performance with fMRI activation and stroke volumes.

Results: Our analyses show that LMCA-R at least 1 year after stroke show a return to typical fMRI language activation patterns and that there is a compensatory reorganization of language function in LMCA-NR patients with shifts to the right hemispheric brain regions. Further, with increasing strength of the left-hemispheric fMRI signal shift there are associated improvements in performance as tested with standardized linguistic measures. A negative correlation between the size of the stroke and performance on some of the linguistic tests is also observed.

Conclusions: This right-hemispheric shift as a mechanism of post-stroke recovery in adults appears to be an ineffective mode of language function recovery with increasing right-hemispheric shift associated with lower language performance. Thus, normalization of the post-stroke language activation patterns is needed for better language performance while shifts of the activation patterns to the non-dominant (right) hemisphere and/or large stroke size are associated with decreased linguistic abilities after stroke.

Figures

Figure 1

Example of using the lesion mask for the brain extraction and normalization steps. (A) Standard brain extraction of lesioned anatomical MRI (left) results in removal of viable tissue beyond the stroke lesion (middle) and subsequent misregistration to standardized space (right). (B) The lesion mask (in red) was traced on each subject’s anatomical MRI (left) and applied to achieve good results during the brain extraction algorithm (middle) and subsequent normalization to standardized space (right). Images are presented in radiological convention (left=right).

Figure 2

Group composite maps depicting lesion overlap between subjects in (A) LMCA patients with Token Test ≥41 (LMCA-R; n=9) and (B) LMCA patients with Token Test ≤40 (LMCA-NR; n=18). Images are presented in radiological convention (left=right) and lesion maps are overlaid onto one of the stroke subject’s anatomical scan in Talairach space with slices ranging from z=−34 to z=+62 (left to right).

Figure 3

Group composite activation maps for the SD/TD task for (A) LMCA-R and (B) LMCA-NR patients. Both groups show overall typical BOLD activation patterns during semantic processing with increased activation (in orange) in medial frontal, left lateral frontal and left/bilateral parietal regions and decreased activation (in blue) in bilateral temporal regions. (C) Group differences in BOLD activation during semantic processing. Compared to LMCA-NR, LMCA-R showed greater increases in activation (in orange) in the bilateral (right>left) cerebellum (1), left superior parietal lobule (3) and the left superior frontal gyrus (4). LMCA-R also showed a greater decrease in activation (in blue) than LMCA-NR in the right superior temporal gyrus (2). Activation clusters in all images are significant after correction for multiple comparisons at a corrected p<0.05 (voxelwise p<0.05, minimum cluster of 65 contiguous voxels). Images are presented in radiological convention (left=right) and group activation maps are overlaid onto one of the stroke subject’s anatomical scan in Talairach space with slices ranging from z=−34 to z=+62 (left to right). The clusters in (C) showing significant group activation differences were defined as regions of interest (ROIs 1–4) for use in correlation analyses; for each ROI, the average t-score was extracted from each subject’s GLM map. (c2) shows significant associations (Bonferroni corrected) between fMRI activation in ROI 2 and Controlled Oral Word Association Test (COWAT) performance. (c4) shows significant associations (Bonferroni corrected) between fMRI activation in ROI 4 and language performance on the Boston Naming Test (BNT), Semantic Fluency Test (SFT), Peabody Picture Vocabulary Test (PPVT), and the Complex Ideation subtest of the Boston Diagnostic Aphasia Examination (BDAE). On the scatterplots, data points in orange are LMCA-R subjects and in blue are LMCA-NR subjects.