Abstract DP246: Neurobiological Mechanisms of tDCS as an Adjuvant to Shortened Phonomotor Treatment for Chronic Post-Stroke Aphasia

Introduction: Adjuvant therapies in aphasia rehabilitation have significant potential to reduce the costs and resources required for intensive speech-language therapies. Our research group conducted a proof-of-principle pilot study to investigate the effects of transcranial direct current stimulation (tDCS) combined with a shortened course of phonological treatment (sPMT). The design of our study allowed us to explore the brain mechanisms associated with the sPMT+tDCS approach. Methods: The pilot study utilized a double-blind, parallel-group design, involving 30 hours of sPMT paired with 1 mA of tDCS (anode over the left inferior frontal gyrus and cathode over the right) that was synchronized at the beginning of the intervention for individuals with chronic post-stroke aphasia. We report data from six participants, matched on aphasia severity (three receiving active treatment and three receiving sham treatment). Phonological production and confrontation naming measures were administered at baseline, immediately post-intervention, and at a three-month follow-up. Structural and resting-state functional magnetic resonance imaging (rsfMRI) were collected at baseline and post-intervention. Results: Repeated measures ANOVA of the phonological measures revealed a significant group-by-time interaction. The sPMT combined with active tDCS group showed an improvement in phonological processing from baseline to post-intervention, while no such improvement was observed in the sham group. These gains were maintained by the active group at the three-month follow-up. Confrontation naming did not show significant time effects or time-by-group interactions for either active or sham tDCS. The estimated current density (J) using structural MRI indicated that J is influenced by core lesion volume and the distance between the two tDCS electrodes. This finding highlights the importance of considering lesion volume, head size, and precise electrode positioning. Our rsfMRI analysis detected significant group-by-time interactions, revealing that most connections exhibited greater increases in connectivity for the active group. These connectivity improvements were observed in both domain-specific and domain-general networks associated with enhanced phonological production and maintenance of gains. Conclusion: Our work lays a foundation for optimizing tDCS and understanding the brain mechanisms linked to strengthening the language system in individuals with chronic post-stroke aphasia.