Abstract
In the dual-route language model, the dorsal pathway is known for sound-to-motor mapping, but the role of the ventral stream is controversial. With the goal of enhancing our understanding of language models, this study investigated the diffusion characteristics of candidate tracts in aphasic patients. We evaluated 14 subacute aphasic patients post-stroke and 11 healthy controls with language assessment and diffusion magnetic resonance imaging. Voxel-based lesion-symptom mapping found multiple linguistic associations for the ventral stream, while automated fiber quantification (AFQ) showed, via reduced fractional anisotropy (FA) and axial diffusivity with increased radial diffusivity (all corrected p < 0.05), that the integrity of both the left dorsal and ventral streams was compromised. The average diffusion metrics of each fascicle provided by AFQ also confirmed that voxels with significant FA-language correlations were located in the ventral tracts, including the left inferior fronto-occipital fascicle (IFOF) (comprehension: r = 0.839, p = 0.001; repetition: r = 0.845, p = 0.001; naming: r = 0.813, p = 0.002; aphasia quotient: r = 0.847, p = 0.001) and uncinate fascicle (naming: r = 0.948, p = 0.001). Furthermore, point-wise AFQ revealed that the segment of the left IFOF with the strongest correlations was its narrow stem. The temporal segment of the left inferior longitudinal fascicle was also found to correlate significantly with comprehension (r = 0.663, p = 0.03) and repetition (r = 0.742, p = 0.009). This preliminary study suggests that white matter integrity analysis of the ventral stream may have the potential to reveal aphasic severity and guide individualized rehabilitation. The left IFOF, specifically its narrow stem segment, associates with multiple aspects of language, indicating an important role in semantic processing and multimodal linguistic functions.
Highlights
Language is an advanced cortical function, closely associated with social activity and information transmission, and language deficits lead to severely impaired quality of life
Fourteen patients with post-stroke aphasia were enrolled based on the Aphasia Battery of Chinese (ABC) language scale and magnetic resonance imaging (MRI) scans, including the diffusion tensor imaging (DTI) sequence
automated fiber quantification (AFQ) have been utilized in previous research [46], our DTI study is the first to use it in subacute post-stroke patients with language deficits
Summary
Language is an advanced cortical function, closely associated with social activity and information transmission, and language deficits lead to severely impaired quality of life. The classical model, focusing on cortical language regions, including the Broca and Wernicke areas, cannot explain the clinical problems caused by lesions outside the classical regions [6]. Brain sample reexaminations of the first two patients with Broca’s aphasia revealed that damage was not restricted to the cortical surface, and involved deep subcortical white matter [7, 8]. A subsequent large-scale study demonstrated that most cerebral infarction lesions involved white matter, and behavioral disorders caused by damaged white matter, including disconnection syndromes, are not uncommon [9]. Damage to several specific white matter tracts was proved to contribute to severe language impairment [7]. The subcortical white matter tracts transmit information and promote collaboration between components of the distributed language network [3, 4]
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