Synchronizing Oscillatory Brain Activity to Treat Post-Stroke Aphasia

PROJECT SUMMARY/ABSTRACT Transcranial alternating current stimulation (tACS) is increasingly used to enhance perceptual and cognitive performance in healthy individuals and in individuals with neurological and psychiatric disorders. But even after >8000 publications and strong evidence suggesting positive effects, clinical applications of tACS to improve

language outcomes in stroke survivors with aphasia (SWA) are few and far between. Little guidance is available from the existing literature to effectively plan tACS treatment protocols in SWA. The selection of tACS parameters is complicated by large underlying anatomical and functional heterogeneity

after stroke. Given this heterogeneity, our overarching hypothesis is that tACS efficacy will depend on stimulation target selection, frequency and effectiveness of electric field coverage at individual patient level. Our proposed project seeks to examine the effects of individualized selection of tACS targets and frequency (Aim 1), based

on detailed analyses of lesion location, residual functional activity, and residual brain oscillatory activity on phonological short-term memory (pSTM) performance in chronic SWA. We hypothesize that individualized tACS will enhance the size and reliability of tACS response. This project is motivated by individual variability that we

observed in our preliminary data from 9 SWA. Independent of Aim 1, we will also explore how stroke characteristics influence residual functional and oscillatory brain activity underlying pSTM (Aim 2). Our project fits perfectly within the scope of the R21 Exploratory/Developmental grant because it is at “early and

conceptual stages” and is within one of NIDCD’s scientific foci—treating “disorders of human communication”. Notable innovations of the proposed project are our novel use of (1) multimodal structural, functional and electrophysiological techniques to optimize tACS parameters in individual SWA, and (2) individualized electric

field models to optimize tACS electrode arrangements, both in service to increase the efficacy of tACS. While ideally aphasia therapy would be ecologically valid and would enhance functional communication outcomes, the proposed use of a lab-based controlled task and focus on pSTM is needed at this stage to gain a

better understanding of the effects of tACS in SWA. This knowledge will facilitate future use of tACS as an adjunctive treatment to boost functional outcomes. Presently, a proof-of-concept study is crucial to establish a sound methodological basis for developing effective neurorehabilitation strategies using tACS in SWA.