Optimizing speech motor learning with neuromodulation: Behavioral outcomes and neural mechanisms

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PROJECT SUMMARY/ABSTRACT Stroke is a leading cause of disability in the United States, frequently leading to speech impairment that creates barriers to participation in professional, social, and family settings. While recovery can be promoted with speech motor learning treatment, residual disability remains a prominent issue. The long-term goal of this research is to enhance intervention outcomes for individuals with acquired speech impairment by combining theoretically-guided behavioral intervention with targeted neuromodulation. The main objectives of this proposal are to verify the role of left ventral premotor and motor cortices in speech motor learning and to establish that transcranial direct current stimulation (tDCS) can enhance speech motor learning treatment by strengthening the cortical speech network. The central hypothesis of this proposal is that speech recovery in chronic stroke can be improved by stimulating perilesional left ventral premotor and motor cortices, thereby promoting their engagement during speech motor learning treatment and strengthening the cortical speech network through associative learning. The central hypothesis will be tested by pursuing three specific aims: 1) Establish the neural regions that underlie tDCS-facilitated speech motor learning; 2) Determine the extent to which active tDCS with individualized electrode placement can enhance speech motor learning intervention relative to sham tDCS in impaired speakers with apraxia of speech; and 3) Determine the functional connectivity changes associated with speech motor learning-based intervention with active vs. sham tDCS in impaired speakers with apraxia of speech. Under the first aim, the proposed research will systematically verify the role of left ventral premotor and motor cortices in tDCS-facilitated speech motor learning using three controls: electrode polarity, electrode position, and presence of active current. For the second aim, single- subject intervention experiments will be used to evaluate the extent to which tDCS enhances apraxia treatment outcomes, using individualized current modeling to target left ventral premotor and motor cortices. The third aim determines the extent to which the treatment conditions in Aim 2 can change functional connectivity measured with resting-state functional neuroimaging. The proposed research is innovative, in the applicant's opinion, because it combines practice-based speech treatment with targeted tDCS to intensify Hebbian plasticity and measures the extent to which this approach changes functional connectivity in the speech network. This research will be significant because it will establish the combined effectiveness of speech motor learning treatment and tDCS in AOS, an understudied condition. Understanding the interaction of treatment and neuromodulation will build capacity to optimize chronic stroke recovery, with direct application to enhancing speech skills to improve communication ability and quality of life.