Mechanisms associated with tDCS as an adjuvant to shortened phonomotor treatment in chronic post-stroke aphasia

Adjuvant therapies in aphasia rehabilitation may help reduce the cost and clinical resources required for intensive speech-language interventions. We conducted a proof-of-principle pilot study to evaluate whether transcranial direct current stimulation (tDCS) paired with a shortened course of phonomotor treatment (sPMT)—targeting sounds and nonwords but not real words—enhances phonological production in chronic post-stroke aphasia, and to examine the neural mechanisms underlying this approach. Using a double-blind, parallel-group design, participants received 30 h of sPMT combined with 1 mA tDCS (anode/cathode over left/right inferior frontal gyrus) delivered at the start of each intervention session. Here, we report data from six older male participants matched on aphasia severity (active: n = 3; sham: n = 3). Phonological production and confrontation naming were assessed at baseline, immediately post-intervention, and at 3-month follow-up. Structural and resting-state functional MRI (rs-fMRI) were acquired at baseline and post-intervention. Repeated-measures ANOVA revealed a significant group-by-time interaction for phonological production, with the active tDCS + sPMT group showing gains from baseline to post-intervention that were maintained at 3 months, whereas the sham group showed no significant improvement. Confrontation naming showed no significant effects of time or group. MRI-based estimates of current density (J) indicated that J varied systematically with lesion volume and inter-electrode distance, underscoring the importance of individualized electrode placement. rs-fMRI analyses demonstrated significant group-by-time interactions, with greater connectivity increases in the active versus sham group across domain-specific and domain-general networks. These preliminary findings suggest that active tDCS may enhance the effects of sPMT on phonological production and provide mechanistic support for individualized, network-informed neuromodulatory approaches in post-stroke aphasia rehabilitation.