Enhancing speech fluency in adults who stutter: A randomised controlled trial of anodal tDCS combined with fluency-shaping intervention.

Authors

Kowsar Esfandeh, Michael Nitsche, Hamid Karimi, Abbas Ebadi, Ahmad Reza Khatoonabadi

Published in

Journal of fluency disorders. Volume 88. Pages 106221. Apr 28, 2026. Epub Apr 28, 2026.

Abstract

Stuttering is a neurodevelopmental disorder that typically emerges in childhood and may persist into adulthood. The current study hypothesized that adults with persistent stuttering who received active anodal transcranial direct current stimulation (tDCS) over the left inferior frontal gyrus would demonstrate significantly greater improvements in speech fluency compared to those who received sham stimulation.
A randomized, double-blind, sham-controlled clinical trial was conducted to evaluate the efficacy of a combined therapeutic approach. Thirty adults diagnosed with moderate to severe stuttering (6 females, 24 males; M = 30.60 years, SD = 10.15) were randomly assigned to either an anodal tDCS group or a sham stimulation group. Participants in the anodal group received fluency shaping therapy concurrently with anodal transcranial direct current stimulation (2 mA), while those in the sham group underwent the same behavioral therapy alongside sham stimulation. The tDCS was targeted over the left inferior frontal gyrus. Each participant completed ten 20-minute sessions over five consecutive days. Speech fluency outcomes were measured pre- and post-intervention.
The anodal tDCS group demonstrated significantly greater reductions in %SS, NAT, and SR compared to the sham group across all post-intervention time points (p < .05). Regarding the OASES, no significant between-group differences were observed at any time point; however, both groups demonstrated significant within-group improvements from baseline to the 3-month follow-up.
These findings suggest that tDCS, when combined with behavioral fluency interventions, can enhance speech fluency in adults who stutter. tDCS may therefore serve as a promising adjunctive technique to augment the effectiveness of conventional fluency therapies.

PMID:
42092230
Bibliographic data and abstract were imported from PubMed on 07 May 2026.

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