The Impact of Anodal tDCS on Verbal and Nonverbal Functional Communication in Subacute Aphasia-An Observational Study

Background/Objectives: While a growing number of studies have demonstrated positive effects of adjuvant anodal transcranial direct current stimulation (tDCS) on linguistic performance in aphasia, evidence for corresponding effects on verbal and-in particular-nonverbal functional communication remains absent. This is a critical gap, given that restoring everyday communicative competence is the ultimate goal of speech and language therapy (SLT). In the present observational study, we investigated the add-on effect of anodal tDCS over language-relevant left-hemispheric areas on verbal and nonverbal functional communication in n = 34 individuals with subacute aphasia and examined the relationship between communicative and linguistic change. Methods: Participants underwent two consecutive two-week therapy phases (P1, P2), each consisting of 10 SLT sessions. Severity-specific linguistic and communicative assessments were administered before, between, and after both phases: the Aachen Aphasia Test (AAT; n = 26) combined with the Amsterdam-Nijmegen Everyday Language Test (ANELT, A-scale), and the Bielefeld Aphasia Screening Rehabilitation (BIAS-R; n = 8) combined with the Scenario Test. During P2, SLT was supplemented by online anodal tDCS. Results: Overall test performance improved significantly more in tDCS-supported P2 compared to P1 (AAT profile level, p < 0.001; BIAS-R mean percentage value (MPW), p = 0.027; ANELT A-scale raw score Version 1, p = 0.081, and version 2, p = 0.038; and Scenario Test total score, p = 0.003). Significant correlations between AAT profile level and ANELT total scores were found across all time points. Between the MPV and subtests of the BIAS-R and the Scenario total score, there was a tendency toward decreasing correlation levels from T1 to T3. Conclusions: To our knowledge, this is the first study demonstrating that adjuvant tDCS in subacute aphasia enhances not only linguistic performance but also verbal and nonverbal functional communication beyond SLT alone-assessed with standardized, performance-based, ecologically valid instruments.