Impact of neuromodulation on post-stroke aphasia: a multimodal randomized controlled study

BackgroundTranscranial direct current stimulation (tDCS) combined with speech and language therapy (SLT) may increase the effectiveness of recovery in post-stroke aphasia. However, inconsistent responses have been observed, in part due to small sample sizes, limited comprehensive assessments, and poor mechanistic understanding of intervention related recovery. MethodsUsing a double-blind, randomized, sham-controlled design, we investigated the efficacy of anodal Brocas tDCS combined with SLT over five 20-minute daily sessions in 45 chronic stroke patients. EEG and DTI were used to explore treatment-mediated neuroplastic mechanisms. The primary outcome measures were linguistic skills evaluated by the Western Aphasia Battery-Revised before and after the intervention. ResultsCompared to sham (SLT + placebo), tDCS patients improved significantly more in aphasia quotient, auditory verbal comprehension, and spontaneous speech. While tDCS improved both expressive and receptive domains, sham only improved expressive language. EEG showed recovery in both groups to rely predominantly on the contralesional side, particularly the right middle temporal area (T4). While tDCS induced recovery correlated with changes in the faster frequencies (e.g., alpha, beta), sham mediated recovery correlated with changes in the slower frequencies (e.g., theta, delta). Furthermore, reduced beta coherence between T3 and T4 was associated with repetition gains specific to tDCS. Furthermore, improved spontaneous speech in tDCS was associated with decreased mean diffusivity in superior cerebellar peduncle. Given this regions connectivity with contralateral cortical regions, this finding extends and aligns with the EEG signatures of neuroplasticity in right-lateralized cortical regions, highlighting the role of cerebro-cerebellar connections in language recovery. ConclusionsOur findings support the use of anodal Brocas tDCS for enhancing both expressive and receptive language domains in chronic aphasia. To the best of our knowledge, this study represents the first multimodal neuroimaging (EEG, DTI) study to uncover mechanistic differences between tDCS and behavioral mediated aphasia recovery, and the first to identify a cerebellar white matter marker of language recovery following tDCS. Clinical Trial Registrationhttp://www.clinicaltrials.gov [NCT03699930]