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Front. Neurol. | doi: 10.3389/fneur.2018.00089

Multifunctional roles of the ventral stream in language models: advanced segmental quantification in post-stroke aphasic patients

 Jie Zhang1, 2,  Xuehu Wei3, Sangma Xie4,  Zhen Zhou5, Desheng Shang2, Renjie Ji2, Yamei Yu2, Fangping He2, Xiangming Ye1 and  Benyan Luo2*
  • 1Zhejiang Provincial People's Hospital, China
  • 2First Affiliated Hospital, College of Medicine, Zhejiang University, China
  • 3University of Electronic Science and Technology of China, China
  • 4Hangzhou Dianzi University, China
  • 5Zhejiang University, China

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 (UF) (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 (ILF) 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.

Keywords: Aphasia, Stroke, Diffusion tensor imaging (DTI), ventral pathway, language model

Received: 27 Nov 2017; Accepted: 08 Feb 2018.

Edited by:

Itamar Ronen, Leiden University, Netherlands

Reviewed by:

Konstantinos Kalafatakis, University of Bristol, United Kingdom
Martin Gorges, Department of Neurology, University of Ulm, Germany  

Copyright: © 2018 Zhang, Wei, Xie, Zhou, Shang, Ji, Yu, He, Ye and Luo. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Benyan Luo, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China, luobenyan@zju.edu.cn