Presentation
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Observed timing and facilitation effects after theta-burst stimulation of the reading network.
Poster C25 in Poster Session C, Friday, October 7, 10:15 am - 12:00 pm EDT, Millennium Hall
Rachael M. Harrington1, Lisa C. Krishnamurthy1,2, Alexandra Ossowski1, Mykayla Jeter1,2, Adriane Davis1, Robin Morris1, C. Nikki Arrington1; 1Georgia State University, 2Atlanta Department of Veterans Affairs
Introduction: Theta-burst stimulation (TBS) is a well-established technique for delivery of repetitive transcranial magnetic stimulation. However, there is some debate as to the reliability and reproducibility of behavioral effects of TBS. In this study, we sought to evaluate the inhibitory versus excitatory effects of continuous and intermittent TBS (cTBS, iTBS) after stimulation of key nodes of the reading system and to observe at what time point after stimulation the greatest effects of stimulation were observed. Methods: 21 participants were recruited into this study. Participants completed a baseline forced-choice reaction time phonological discrimination task and received cTBS or iTBS to the supramarginal gyrus (SMG) or middle temporal gyrus (MTG) or no stimulation control condition. Immediately following stimulation, participants performed the same reading tasks at four timepoints, approximately 15 , 30 , 60 , and 70 minutes post stimulation. Percent change from baseline in reaction time of correct trials was calculated for each timepoint. Results: For all sites, there was a significant effect of time after stimulation (t = -2.9, p < 0.003) but not of stimulation type (t=-.99, p <0.4, (F, (2,162) = 4.817, p < 0.01, r2 = .056) on percent change in reaction time. In the SMG condition, multiple linear regression of time after stimulation and type of stimulation in the SMG condition indicated a significant effect of time after stimulation (t = -2.3, p <0.03) but not of stimulation type (t = -1.2, p <0.2) (F(81,2) = 3.5, p <0.04, r2 = 0.08). This pattern was also evident in the MTG condition. In the MTG condition, there was a significant effect of time after stimulation (t = -2.7, p < 0.05) but not of stimulation type (t = .13, p > 0.9) (F(63,2) = 2.6, p <0.08, r2 = 0.08). In the no stimulation condition, regression of percent change from baseline and time after stimulation (t = -.3, p < 0.8) was not significant (F(1,13) = 0.07, p < 0.8, r2 = .006). Conclusion: In summary, cTBS and iTBS showed a facilitatory effect on change in reaction time compared to control. These data support recent work in the motor system that suggest that both cTBS and iTBS led to facilitation of MEPs (Ozdemir et al., 2021). Percent change in reaction time improved the most at the last two time points (60-70 minutes post stimulation) and this effect was not seen in the no-stimulation condition suggesting the observed effect is beyond that expected of traditional task practice effects. These data suggest that the greatest impact of TBS in the language system is much later in time than those reported in the motor system. While these results need to be replicated in other datasets before we can draw firm conclusions, they indicate that we need to be more critically analyzing the effects of cTBS and iTBS and at what timepoint after stimulation outcome measures are taken.
Topic Areas: Disorders: Acquired, Reading