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White matter substrates underlying recovery of spelling in post-stroke aphasia

Celia Litovsky1*, Kerry Qualter1, Nomongo Dorjsuren1 and Brenda Rapp1
  • 1 Johns Hopkins University, United States

Introduction. Given that written language production (spelling) is among the most common complaints of stroke survivors (Hillis and Tippett, 2014), there is considerable interest in identifying the neural substrates of spelling and its recovery. Although research has identified that multiple cortical regions, including the left fusiform gyrus, inferior frontal gyrus, and posterior parietal cortex, are recruited for spelling (Rapp et al., 2016), no study has investigated its white matter substrates. Twenty-one participants with post-stroke dysgraphia participated in a three-month spelling rehabilitation and underwent diffusion-weighted imaging prior to spelling training. On the basis of previous studies implicating the left arcuate fasciculus (AF), inferior fronto-occipital fasciculus (IFOF), and inferior longitudinal fasciculus (ILF) in reading (Vandermosten et al., 2012 Epelbaum et al., 2008), we investigated these tracts’ roles in spelling impairment and recovery. We also examined the vertical occipital fasciculus (VOF), a newly (re)discovered tract connecting the orthographic processing areas of the posterior parietal cortex and the fusiform gyrus (Yeatman et al., 2014). In order to identify the white matter tracts that support spelling and its recovery, we evaluated if white matter integrity (measured by tract volume) of these tracts predicted the pre-treatment degree of spelling impairment and treatment effectiveness (e.g., spelling improvement on trained items) in participants with chronic post-stroke spelling deficits. Methods. Twenty-one participants (7 females, age 60 +/- 2.3 years, 81 +/- 12.3 months post-stroke) with a single left hemisphere stroke underwent T1-weighted and diffusion-weighted imaging (b=0, b=1500 s/mm2) and completed a three-month behavioral spelling rehabilitation. Whole-brain probabilistic tractography was performed in ExploreDTI (Leemans et al., 2009) using constrained spherical deconvolution (Jeurissen et al., 2011), and 10 white matter tracts (right and left: long and posterior segments of the AF, VOF, IFOF, ILF) were segmented according to the Catani and Thiebaut de Schotten atlas (2008) and the segmentation protocol of Takemura et al. (2016). Each tract’s volume was entered into four stepwise regression analyses to predict pre-treatment spelling ability, spelling improvement on trained items, generalization to untrained items, and training rate. Results. Regression models significantly predicted participants’ pretreatment spelling ability [F(3,10) = 8.28, p = .005, Adjusted R2 = 0.627], spelling improvement on training items [F(4,9) = 17.02, p < .001, Adjusted R2 = 0.831], and training rate [F(4,9) = 17.2, p < .001]. With regard to the specific tracts, pretreatment spelling scores were significantly predicted by integrity of the right posterior segment of the AF and bilateral VOF. Spelling improvement on training items was predicted by the integrity of the left posterior AF and left IFOF, and training rate was predicted by the integrity of the left ILF, right posterior AF, and right VOF. Conclusions. The white matter structures that underlie spelling and its recovery largely overlap with those supporting other language skills, although we report novel evidence for the unique role of the VOF in orthographic processing and rehabilitation. These findings are generally consistent with previous research identifying differences in temporoparietal anisotropy in individuals with dyslexia compared to typical readers (Klingberg et al., 2000).

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Acknowledgements

This research was funded by a National Science Foundation Graduate Research Fellowship to Celia Litovsky and National Institutes of Health grant DC006740 to Brenda Rapp.

References

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Keywords: Constrained spherical deconvolution (CSD), diffusion weighted imaging (DWI), spelling, Dysgraphia treatment, predictors of aphasia recovery

Conference: Academy of Aphasia 57th Annual Meeting, Macau, Macao, SAR China, 27 Oct - 29 Oct, 2019.

Presentation Type: Platform presentation

Topic: Eligible for student award

Citation: Litovsky C, Qualter K, Dorjsuren N and Rapp B (2019). White matter substrates underlying recovery of spelling in post-stroke aphasia. Front. Hum. Neurosci. Conference Abstract: Academy of Aphasia 57th Annual Meeting. doi: 10.3389/conf.fnhum.2019.01.00067

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Received: 06 May 2019; Published Online: 09 Oct 2019.

* Correspondence: Ms. Celia Litovsky, Johns Hopkins University, Baltimore, United States, celialitovsky@gmail.com