Phonological intervention and tDCS in PPA (Nickels et al., 2025)

Purpose: Despite recognition of the underlying phonological impairment observed in the logopenic and nonfluent variants of primary progressive aphasia (PPA), there is relatively little treatment research directed toward strengthening phonological skills. In this study, we focused on remediating phonological deficits in logopenic and nonfluent PPA. Specifically, we hypothesized that behavioral intervention intended to strengthen phonological manipulation skills and sound–letter correspondences—coupled with transcranial direct current stimulation (tDCS)—would improve language abilities, especially in the written modality.

Method: Twelve individuals with logopenic or nonfluent variants of PPA and 24 neurotypical adults completed neuropsychological assessment that documented spoken and written language deficits in those with PPA. Phonological skills were consistently impaired in relation to other language processes. Following a double-blind, crossover design, six individuals with PPA were randomized to receive active tDCS with phonological intervention during the first treatment phase, and after a 2-month break, they received a second phase of behavioral intervention paired with sham tDCS. The other six individuals were randomized to receive sham first and active tDCS second. Language skills were evaluated before and after each treatment phase and 2 months after the intervention.

Results: Both treatment groups (tDCS-first and sham-first) made significant improvement in phonological transcoding skills in response to behavioral intervention, but those who received active tDCS first showed stronger gains in phonological manipulation ability. This group also showed positive changes in written narratives, which contained more grammatical sentences with increased meaningful content and more accurate spelling.

Conclusions: These data provide compelling evidence supporting an approach that targets phonological deficits in logopenic and nonfluent PPA. Specifically, we found that improved phonological skills resulted in better functional communication ability (text-level writing) relevant to everyday life. Positive outcomes were strongest when tDCS was combined with behavioral treatment from the beginning, suggesting that this combination may potentiate positive changes that extend beyond the initial stimulation period.

Supplemental Material S1. fMRI task design.

Supplemental Material S2. fMRI data processing and analysis.

Supplemental Figure S1. Results of voxel-based morphometry analysis showing regions of significant gray matter volume loss in (A) the tDCS-first group and sham first-groups compared to controls, (B) the tDCS-first group compared to the sham-first group, and (C) those with lvPPA compared to those with nfvPPA.

Supplemental Figure S2. Modeling of electrical fields induced by tDCS using SimNIBS4 in two representative participants: (A) Position of anode (yellow over F5) and reference electrode (blue over Fp2); (B) Current flow from anode to cathode depicted with directional fields normal to the cortical surface. The positive values (red lines) indicate inward field entering the cortical surface, and negative values (blue lines) indicate outward electrical field leaving the surface. For the anode over F5, the magnitude of the induced electrical field was the strongest in the left frontal and prefrontal regions; (C) Position of anode (yellow over CP5) and reference electrode (blue over Fp2); (D) For the anode over CP5, the magnitude of the induced electrical field was the strongest in the left posterior parietal and temporal regions.

Supplemental Figure S3. Transcripts of written picture descriptions (WAB Picnic Scene) not included in the main text for participants from the tDCS-first and sham-first groups before and after Phase 1 treatment, Phase 2 treatment, and at follow-up.

Supplemental Table S1. tDCS-first (n = 6) and sham-first (n = 6) group and individual subject performance on the Western Aphasia Battery-Revised (WAB-R).

Supplemental Table S2. Individual subject performance in the tDCS-first and sham-first groups on a comprehensive assessment battery at pre-treatment, with data organized from most to least impairment on a sound blending task (APB). Values reported in percent unless otherwise indicated.

Supplemental Table S3. Psycholinguistics properties of pre- and post-treatment stimuli probes (with examples) for blending words, blending nonwords, and reading nonwords administered before and after each treatment session.

Supplemental Table S4. Example word and nonword stimuli used during treatment at the 1-, 2-, and 3-syllable levels.

Nickels, K., Beeson, P. M., & Kielar, A. (2025). Addressing phonological deficit in primary progressive aphasia with behavioral intervention and transcranial direct current stimulation. Journal of Speech, Language, and Hearing Research. Advance online publication. https://doi.org/10.1044/2024_JSLHR-24-00250