Background: Language is one of the most lateralized brain functions, and cortical language areas
are similarly asymmetrical. In a previous study, we presented evidence that perinatal
left-hemispheric stroke is usually associated with functionally successful right-hemispheric
language reorganization. It remains unclear, however, whether language-reorganization
is associated with anatomical differences in the reorganized hemisphere.
Hypothesis: Exploratory voxel-wise gray matter comparison of patients with right-hemispheric
language-reorganization after perinatally acquired left hemispheric stroke to normal
controls with left-hemispheric language-organization limited to the right hemisphere.
Methods: Prospective data collection of 8 patients (age 9 to 26, 3 female) with perinatally
acquired left-hemispheric brain lesions as well as 29 normally developing controls
with left-hemispheric language-organization (age 8 to 29, 14 female). We used a Siemens
1.5 Avanto scanner to acquire whole brain functional echoplanar images while patients
and controls performed the vowel identification task, reflecting language production.
Anatomical images were acquired in the form of a T1-weighted three-dimensional dataset
(1x1x1 mm³). Functional and anatomical data was preprocessed and analyzed with SPM12,
CAT12 and custom scripts. We determined the frontal lateralization indices and performed
a voxel-wise comparison of the right hemisphere for gray matter group differences
including age and sex as covariates. For the resulting significance clusters we additionally
calculated the mean hemispheric gray matter volume in homotopic regions of the left
hemisphere.
Results: Six of eight patients showed right-hemispheric language reorganization (LI -0.66;
[-0.89 to -0.34]) whereas the 29 controls had an evident left-dominance (LI 0.85;
[0.62 to 0.96]). There was one controls>patients cluster in right-hemispheric gray
matter indicating a significant group difference (cluster forming threshold p = 0.001,
extent threshold pFEW = 0.05). More specifically, the difference cluster was situated
in the medial temporal gyrus with a cluster-size of 795 voxels and mean cluster-specific
gray matter volumes of 1.81 [1.45–2.15] vs. 1.37 cm³ [1.18–1.57] (RH) and 1.34 [1.02–1.67]
vs. 0.89 [0–1.29] cm³ (LH). Hence, gray matter volume of this right-hemispheric region
in reorganized patients (1.37 cm³) corresponds to the homotopic left-hemispheric region
in left-dominant controls (1.34 cm³) and is significantly smaller (p < 0.001, Mann-Whitney)
compared to the right hemisphere in controls (1.81 cm³).
Discussion: Right-hemispheric language-reorganization seems to lead to a similar cortical volume
in a posterior-temporal area as in homotopic regions of the left hemisphere in left-dominant
controls. The functional relevance of these findings will be investigated further.
