White Matter Correlates of Auditory Comprehension Outcomes in Chronic Post-Stroke Aphasia

Abstract

Neuroimaging studies have shown that speech comprehension involves a number of widely distributed regions within the frontal and temporal lobes. We aimed to examine the differential contributions of white matter connectivity to auditory word and sentence comprehension in chronic post-stroke aphasia. Structural and diffusion MRI data were acquired on 40 patients with chronic post-stroke aphasia. A battery of auditory word and sentence comprehension tests were administered to all the patients. Tract-based spatial statistics were used to identify areas in which white matter integrity related to specific comprehension deficits. Relevant tracts were reconstructed using probabilistic tractography in healthy older participants, and the mean values of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of the entire tracts were examined in relation to comprehension scores. Anterior temporal white matter integrity loss and involvement of the uncinate fasciculus related to word-level comprehension deficits (R_FA = 0.408, P = 0.012; R_MD = -0.429, P = 0.008; R_AD = -0.424, P = 0.009; R_RD = -0.439, P = 0.007). Posterior temporal white matter integrity loss and involvement of the inferior longitudinal fasciculus related to sentence-level comprehension deficits (R_FA = 0.382, P = 0.02; R_MD = -0.461, P = 0.004; R_AD = -0.457, P = 0.004; R_RD = -0.453, P = 0.005). Loss of white matter integrity in the inferior fronto-occipital fasciculus related to both word- and sentence-level comprehension (word-level scores: R_FA = 0.41, P = 0.012; R_MD = -0.447, P = 0.006; R_AD = -0.489, P = 0.002; R_RD = -0.432, P = 0.008; sentence-level scores: R_FA = 0.409, P = 0.012; R_MD = -0.413, P = 0.011; R_AD = -0.408, P = 0.012; R_RD = -0.413, P = 0.011). Lesion overlap, but not white matter integrity, in the arcuate fasciculus related to sentence-level comprehension deficits. These findings suggest that word-level comprehension outcomes in chronic post-stroke aphasia rely primarily on anterior temporal lobe pathways, whereas sentence-level comprehension relies on more widespread pathways including the posterior temporal lobe.

Keywords: aphasia; diffusion tensor imaging; outcome; stroke; white matter.

Figure 1

Lesion overlap of 40 patients. Color bar indicates the number of patients with lesions in each voxel (maximum 27 out of 40).

Figure 2

Tract-based spatial statistics analysis for white matter integrity related to language comprehension. Altered diffusion tensor imaging metrics related to composite WLC (A) and SLC (B) scores controlling for age and lesion volumes (TFCE corrected P < 0.05). Regions with significantly positive correlates of mean fractional anisotropy (FA) (red–yellow) or negative correlates of mean diffusivity (MD), axial diffusivity (AD), and axial diffusivity (RD) (blue–light blue) with individual comprehension scores are overlaid on the FMRIB58 FA skeleton (green), displayed on a template in Montreal Neurological Institute space. WLC, word-level comprehension; SLC, sentence-level comprehension.

Figure 3

Probabilistic maps of reconstructed ventral and dorsal pathways related to language. (A) Schematic representation of expected tracts in Montreal Neurological Institute space. (B) Reconstructed inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), uncinate fasciculus (UF), and arcuate fasciculus (AF) in native space of a control subject. (C) Group-based probability maps of IFOF, ILF, UF, and AF derived from probabilistic tractography in healthy older subjects (at least 50% subjects of each voxel).

Figure 4

Partial correlations between integrity of entire tracts and auditory comprehension. Mean measures of white matter integrity [fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and axial diffusivity (RD)] of left inferior fronto-occipital fasciculus [IFOF, (A)], inferior longitudinal fasciculus [(ILF), (B)], and uncinate fasciculus [(UF), (C)] were associated with WLC or SLC composite scores, controlling for age, lesion volume, and lesioned voxels in the respective tracts. P < 0.05 with Bonferroni correction. WLC, word-level comprehension; SLC, sentence-level comprehension.