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White matter diffusivity predicts change in sight word reading following continuous theta burst stimulation to the left temporal parietal junction
Poster Session B, Friday, October 25, 10:00 - 11:30 am, Great Hall 3 and 4
C Nikki Arrington1, Ewelina Bledniak1, Brianna Kinnie2, Evelyn Farkas1, Robin Morris1, Fumiko Hoeft2; 1Georgia State University, 2University of Connecticut
Successful coordination of the functional networks underlying reading is highly dependent on the underlying white matter tracts that connect these regions. There are several white matter tracts of interest that support the left-lateralized reading network: the arcuate fasciculus (AF), superior longitudinal fasciculus (SLF), the inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), and the uncinate fasciculus (UF). White matter diffusivity has been shown to predict response to neuromodulation but has not been explored in direct relation to the reading network. Continuous theta burst stimulation (cTBS) is a form of non-invasive brain stimulation that can temporarily inhibit brain activity in targeted brain networks and has been shown to modulate reading ability. It was hypothesized that measures of white matter diffusivity would predict change in reading efficiency following stimulation to the left temporal-parietal junction (TPJ), a targeted node of the dorsal stream of the reading network. Fifty three adults between the ages of 18 and 50 years (M = 22.79, SD = 5.40; 34 female) with a range in reading ability participated in this study. Participants completed the Sight Word Efficiency (SWE) and Phonemic Decoding Efficiency (PDE) subtests of the Test of Word Reading Efficiency-2 prior to and immediately following cTBS to either the left or right LTP or a control site (vertex). Reliable change scores were calculated for SWE and PDE. Participants also completed an MRI session including anatomical and diffusion weighted imaging sequences. FreeSurfer’s Tracts Constrained by Underlying Anatomy (TRACULA) was used to extract fractional anisotropy (FA), a measure of white matter diffusivity, for tracts of interest. Individual hierarchical regressions models including baseline sight word reading, full scale IQ, age, and mean FA where used to predict change in SWE and PDE. Mean FA for six individual tracts significantly predicted change in SWE following cTBS to the left TPJ. Mean FA for the following tracts of interest accounted for the variance in SWE Reliable Change Score: (1) left AF: 38% (F(1, 18) = 10.80, p = .004); (2) right AF: 25% (F(1, 18) = 5.93, p = .025); (3) left SLF II: 21% (F(1, 18) = 4.75, p = .043); (4) right SLF II: 27% (F(1, 18) = 6.68, p = .019); (5) right SLF III: 24% (F(1, 18) = 5.57, p = .030); and (6) left ILF: 23% (F(1, 18) = 5.48, p = .031). ). There were no significant relations between PDE Reliable Change and any white matter tract of interest following cTBS to the left TPJ. Additionally, there were no significant relations between SWE or PDE Reliable Change and any white matter tract of interest following cTBS to either vertex or right TPJ. These findings suggest that increased diffusivity of white matter tracts associated with the left hemisphere reading network and their right hemisphere homologues may support the positive impact of cTBS following stimulation to a targeted node of the reading network. Individual differences in white matter diffusivity may underlie differences in behavioral outcomes following neuromodulation.
Topic Areas: Reading,