An investigation of the effectiveness of bihemispheric tDCS on speech fluency in individuals with stuttering

Stuttering is a neurodevelopmental disorder that causes frequent disruptions in speech flow and affects individuals' lives in many aspects. Recent research on the effectiveness of neuromodulation interventions in stuttering suggests that transcranial direct current stimulation (tDCS) can potentially reduce stuttering symptoms, although it is not clear what the optimal stimulation parameters are, and which specific outcomes benefit from tDCS. 36 individuals with stuttering (32 males, 4 females) completed a randomized, double-blind, sham controlled study. Nineteen participants received 1 mA stimulation for 20 min daily while temporarily achieving speech fluency with metronome-timed speech, while the remaining seventeen participants received the same fluency intervention coupled with sham stimulation. tDCS was delivered with a bihemispheric montage: anodal left inferior frontal gyrus and cathodal right inferior frontal gyrus. Both groups received the interventions for a period of 5 consecutive days. Fluency was assessed while reading and while speaking at baseline, at the end of the 5-day intervention, on each day of the intervention (before and after stimulation), and 1 week after the end of the intervention. Primary and secondary analyses showed no sustained tDCS advantage over sham for percentage of syllables stuttered (%SS) in reading or speaking, or the SSI-4 and OASES subdomains at the end of treatment or at 1-week follow-up. Exploratory within-day analyses, indicated session-bound tDCS benefits for %SS in both reading and speaking. These findings provide limited evidence that tDCS can enhance fluency in the short term, while also underscoring the need for further research to explore its potential long-term benefits.