Poster Slam Session E, Thursday, August 22, 2019, 3:30 - 3:45 pm, Finlandia Hall, Brenda Rapp
White matter tracts underlying orthographic processing: Evidence for the role of the left vertical occipital fasciculus
Celia Litovsky1, Nomongo Dorjsuren1, Kerry Qualter1, Brenda Rapp1;1Johns Hopkins University
Introduction. Orthographic processing has been shown to recruit multiple cortical regions, including the left fusiform gyrus, inferior frontal gyrus and posterior parietal cortex (Rapp et al., 2016). However, it is still unclear which white matter structures underlie orthographic comprehension (reading) and production (spelling/writing). Previous studies have shown that the left arcuate fasciculus (AF), inferior fronto-occipital fasciculus (IFOF), and inferior longitudinal fasciculus (ILF) play a role in orthographic processing (Vandermosten et al., 2012a; Epelbaum et al., 2008), although these results are not consistently found across studies (see Vandermosten et al., 2012b, for a review). Of additional interest is 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 specifically support orthographic processing but not spoken language processing, we evaluated if white matter integrity (measured by tract volume) of these tracts predicted the degree of impairment on measures of spelling, reading, naming, and sentence comprehension in participants with chronic post-stroke language 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 behavioral assessments of reading, spelling, spoken naming, and auditory sentence comprehension. 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 each of the four language domain scores. Results. Regression models significantly predicted each of the four language domain scores [spelling: F(3,10) = 8.28, p=0.005, Adjusted R2=0.627; reading: F(7,6)=7.75, p=0.01, Adjusted R2=0.784; naming: F(4,9)=6.83, p=0.008, Adjusted R2=0.642; sentence comprehension: F(2,11)=3.47, p=0.07, Adjusted R2=0.276]. With regard to the specific tracts, spelling and reading scores were significantly predicted by a bilateral white matter network that largely overlapped with the network supporting spoken naming, including the left IFOF and right posterior segment of the AF. However, only the reading and spelling scores were significantly predicted by the volumes of the left and right vertical occipital fasciculus (VOF). Conclusions. The white matter structures that underlie orthographic processing largely overlap with those supporting other language skills, however, we report novel evidence for the unique role of the VOF in orthographic processing. 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).
Themes: Writing and Spelling, Reading
Method: White Matter Imaging (dMRI, DSI, DKI)
Poster E2