Fixel-Based White Matter Correlates of Sentence Comprehension in Post-Stroke Aphasia

Area of Science:

• Neuroimaging
• Neurolinguistics
• Diffusion MRI

Background:

• Auditory sentence comprehension remains impaired in post-stroke aphasia patients, even with recovered word-level understanding.
• The left perisylvian network is implicated in sentence comprehension, but frontal areas and specific white matter tracts require further investigation.
• Previous research often used voxel-based methods and focused on English, necessitating studies on other languages and using advanced techniques.

Purpose of the Study:

• To precisely map white matter alterations associated with complex sentence comprehension deficits in subacute Mandarin-speaking aphasic patients using fixel-based analysis (FBA).
• To address limitations of prior voxel-based and English-centric research by employing advanced diffusion MRI techniques.
• To refine neurocognitive models of sentence comprehension by identifying specific white matter substrates.

Main Methods:

• Diffusion MRI data from 23 subacute Mandarin-speaking aphasic patients with single left-hemisphere strokes were analyzed.
• Fixel-based analysis (FBA) was used to assess associations between fiber density and cross-section (FDC) and non-canonical sentence comprehension.
• Linear regression and partial Spearman's correlations were employed to examine relationships between FDC values in specific white matter tracts and comprehension accuracy, controlling for covariates.

Main Results:

• Patients comprehended canonical sentences significantly better than non-canonical sentences.
• FBA revealed significant positive correlations between FDC and non-canonical sentence comprehension in tracts including the left superior longitudinal fasciculus (SLF II/III) and arcuate fasciculus (AF).
• Reductions in fiber density were the primary driver of decreased FDC, with fiber cross-section reductions mainly observed in dorsal tracts (SLF III, AF).

Conclusions:

• A distributed left perisylvian white matter network is critical for complex sentence comprehension in Mandarin speakers.
• This study refines neurocognitive models by identifying specific white matter substrates involved in sentence processing.
• Fixel-based analysis (FBA) proves to be a valuable tool for investigating white matter alterations in aphasia research.