White Matter Diffusivity Predicts Change in Sight Word Reading Following Continuous Theta Burst Stimulation to the Left Temporal Parietal Junction

Successful coordination of the functional networks underlying reading is highly dependent on the underlying white matter tracts that connect these regions. Continuous theta burst stimulation (cTBS) can temporarily inhibit brain activity in targeted brain networks and has been shown to modulate reading ability. It was hypothesized that measures of 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 completed sight word and pseudoword fluency measures prior to and immediately following cTBS to either the left or right TPJ or a control site. Participants also completed an MRI session including anatomical and diffusion weighted imaging sequences. Regression analyses were conducted to predict change in reading fluency following cTBS. Tracts associated with the reading network including the arcuate fasciculus, inferior longitudinal fasciculus, and portions of the superior longitudinal fasciculus, as well as the corpus callosum significantly predicted reliable change in a test of word reading efficiency–sight word efficiency subtest following stimulation of the left 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 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.