Transcranial Alternating Current Stimulation as an Adjuvant for Nonfluent Aphasia: A Proof-of-Concept Study

Author(s)

• Lynsey M. Keator
• Lisa Johnson
• Roger Newman-Norlund Ph.D., University of South CarolinaFollow
• Kyler Spell
• Samaneh Nemati
• Leigh Ann Spell
• Dirk B. den Ouden
• Chris Rorden, University of South CarolinaFollow
• Julius Fridriksson Ph.D., University of South CarolinaFollow

Document Type

Article

Abstract

Effective rehabilitation tools are essential for improving language outcomes in chronic aphasia. Speech entrainment is a behavioral treatment that has shown promise in enhancing speech output in nonfluent aphasia, potentially by acting as an external mechanism to synchronize anterior and posterior language regions in the left hemisphere. Transcranial alternating current stimulation has been hypothesized to enhance functional connectivity between brain regions by amplifying endogenous oscillations. This proof-of-concept study explored whether high-definition tACS (HD-tACS) could improve speech fluency in nonfluent aphasia when paired with speech entrainment. In a double-blind, pseudorandomized study, 1 mA of HD-tACS at 7 Hz was applied to anterior and posterior left-hemisphere regions of individuals with nonfluent aphasia (N = 13). Stimulation was applied under three conditions: in-phase, anti-phase, and sham, and paired speech entrainment. Three outcome measures were examined: (1) number of words produced; (2) number of errors, and (3) ‘entrainment’ to the speech entrainment model. Group-level analyses for two of the three outcome measures reveal statistically significant differences between the experimental conditions. In-phase alternating current stimulation yielded more words and better entrainment to the audiovisual model than the sham condition. This study provides promising evidence that HD-tACS could improve speech production in individuals with nonfluent aphasia. These results contribute to growing evidence supporting the therapeutic potential of non-invasive brain stimulation approaches as an adjuvant to traditional behavioral speech-language therapy in stroke survivors.

Digital Object Identifier (DOI)

https://doi.org/10.3390/bioengineering13030372

Publication Info

Published in Bioengineering, Volume 13, Issue 3, 2026, pages 372-.

Rights

© 2026 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.

APA Citation

Keator, L. M., Johnson, L., Newman-Norlund, R., Spell, K., Nemati, S., Spell, L. A., den Ouden, D. B., Rorden, C., & Fridriksson, J. (2026). Transcranial Alternating Current Stimulation as an Adjuvant for Nonfluent Aphasia: A Proof-of-Concept Study. Bioengineering, 13(3), 372.https://doi.org/10.3390/bioengineering13030372