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      Diffusion-tensor imaging of major white matter tracts and their role in language processing in aphasia.

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          Abstract

          A growing literature is pointing towards the importance of white matter tracts in understanding the neural mechanisms of language processing, and determining the nature of language deficits and recovery patterns in aphasia. Measurements extracted from diffusion-weighted (DW) images provide comprehensive in vivo measures of local microstructural properties of fiber pathways. In the current study, we compared microstructural properties of major white matter tracts implicated in language processing in each hemisphere (these included arcuate fasciculus (AF), superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF), inferior frontal-occipital fasciculus (IFOF), uncinate fasciculus (UF), and corpus callosum (CC), and corticospinal tract (CST) for control purposes) between individuals with aphasia and healthy controls and investigated the relationship between these neural indices and language deficits. Thirty-seven individuals with aphasia due to left hemisphere stroke and eleven age-matched controls were scanned using DW imaging sequences. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) values for each major white matter tract were extracted from DW images using tract masks chosen from standardized atlases. Individuals with aphasia were also assessed with a standardized language test in Russian targeting comprehension and production at the word and sentence level. Individuals with aphasia had significantly lower FA values for left hemisphere tracts and significantly higher values of MD, RD and AD for both left and right hemisphere tracts compared to controls, all indicating profound impairment in tract integrity. Language comprehension was predominantly related to integrity of the left IFOF and left ILF, while language production was mainly related to integrity of the left AF. In addition, individual segments of these three tracts were differentially associated with language production and comprehension in aphasia. Our findings highlight the importance of fiber pathways in supporting different language functions and point to the importance of temporal tracts in language processing, in particular, comprehension.

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          Author and article information

          Journal
          Cortex
          Cortex; a journal devoted to the study of the nervous system and behavior
          Elsevier BV
          1973-8102
          0010-9452
          Dec 2016
          : 85
          Affiliations
          [1 ] National Research University Higher School of Economics, Neurolinguistics Laboratory, Moscow, Russia. Electronic address: mivanova@hse.ru.
          [2 ] National Research University Higher School of Economics, Neurolinguistics Laboratory, Moscow, Russia.
          [3 ] National Research University Higher School of Economics, Neurolinguistics Laboratory, Moscow, Russia; Moscow Research Institute of Psychiatry, Department of Speech Pathology and Neurorehabilitation, Moscow, Russia.
          [4 ] National Research University Higher School of Economics, Neurolinguistics Laboratory, Moscow, Russia; University of Groningen, Graduate School for the Humanities, Groningen, The Netherlands.
          [5 ] Center for Speech Pathology and Neurorehabilitation, Moscow, Russia.
          [6 ] Moscow Research Institute of Psychiatry, Department of Speech Pathology and Neurorehabilitation, Moscow, Russia; Center for Speech Pathology and Neurorehabilitation, Moscow, Russia.
          [7 ] National Research University Higher School of Economics, Neurolinguistics Laboratory, Moscow, Russia; Center for Aphasia and Related Disorders, VA Northern California Health Care System, Martinez, CA, USA; Department of Neurology, University of California, Davis, CA, USA.
          Article
          S0010-9452(16)30098-3
          10.1016/j.cortex.2016.04.019
          27289586

          Aphasia, Language, MRI-DTI, Stroke, White matter

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