Effects of Transcranial Direct Current Stimulation (tDCS) on Spaced Discourse Treatment for Chronic Post-Stroke Aphasia

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PROJECT SUMMARY/ABSTRACT Aphasia is a brain disorder, most commonly occurring following stroke, that affects multimodal language abilities. Humans are socially embedded creatures, and thus deficits in communication have dramatic effects on occupational potential and quality of life. Despite the unequivocal and quantifiable benefits of behavioral speech-language therapy, they continue to fall short of a cure, or even desired levels of recovery. One way to increase the benefits of such therapies is to combine them with transcranial direct current stimulation (tDCS). Although this approach has been shown to improve naming, there is limited knowledge of the extent to which this neuromodulatory intervention can complement behavioral treatment to benefit discourse skills and functional communication. This is particularly true for treatment provided on a clinically-feasible schedule (i.e., spaced rather than massed practice). In this project, we take an innovative approach to investigate the effects of tDCS on discourse production in a pilot study of participants with aphasia. We pair active or sham tDCS with Verb Network Strengthening Treatment (VNeST), a behavioral therapy that has demonstrated significant discourse improvement using a spaced treatment schedule. Further, we use a tDCS protocol that has demonstrated benefit with spaced treatment in our preliminary work. AIM 1 determines behavioral effects of pairing active tDCS with spaced discourse treatment, in comparison to a group receiving identical therapy with sham stimulation. An additional goal of this project is to acquire neuroimaging data to inform mechanisms of tDCS effects by identifying graph theoretic network properties related to behavioral change; we use functional magnetic resonance imaging (fMRI) to identify each individual's language network using an adaptive semantic paradigm. In AIM 2A, we examine imaging measures as potential predictors of tDCS effect by calculating two key features of complex networks (integration and segregation) for both task and resting state fMRI. We then analyze the relationship between these variables at baseline and discourse changes measured post-therapy. We anticipate that pre-therapy organization more similar to that of a matched control group will predict greater benefit from treatment, particularly for active stimulation. In AIM 2B, we assess post-therapy changes in the language network, including changes in functional connectivity for the region targeted by tDCS (inferior frontal gyrus; IFG). We predict that the betweenness centrality of IFG within this network will increase significantly during both task and rest for the active stimulation group compared to sham (approaching that of controls), and this increase will be associated with discourse improvement. Our findings will increase understanding of (i) tDCS effects on an evidence-based aphasia treatment provided on a spaced schedule, (ii) language network properties associated with therapy benefit, and (iii) how targeted stimulation changes this network. Thus, we will provide insight into how tDCS might be combined with current clinical practice, as well as the mechanisms through which it induces adaptive neuroplasticity to produce meaningful functional outcomes in aphasia.!