An investigation of the effect of 5 consecutive days of bihemispheric tdcs on speech fluency in individuals with stuttering

Stuttering is a neurodevelopmental disorder that affects the lives of individuals in many aspects by causing frequent disruptions in speech flow, which is seen in 1% of adults. In recent years, with the increasing interest in neurological interventions in the field of stuttering, the effect of brain stimulation on speech fluency in order to reduce stuttering symptoms and to better understand stuttering has been investigated, and it is seen that tDCS has the potential to improve fluency. In this study, it was aimed to investigate the effect of 5 consecutive days of bi-hemispheric (anodal to left IFG, cathodal to right IFG) stimulation on speech fluency in individuals with stuttering. The hypothesis of the study is that bihemispheric stimulation applied consecutively for 5 days will provide a significant improvement on speech fluency by creating a cumulative effect. 36 individuals with stuttering (32 males, 4 females) completed a randomised, double-blind, sham-controlled study of bihemispheric transcranial direct current stimulation. Nineteen participants received 1 mA stimulation for 20 min daily while temporarily achieving speech fluency with metronome-timed speech, while the other seventeen participants received the same fluency intervention with sham stimulation. Speech fluency was assessed at baseline, before and after the intervention on each day of the 5-day intervention, and 1 week after the end of the intervention during reading and speaking. According to the change from baseline to the end of the intervention and 1 week after the intervention, the scores of the group receiving tDCS did not show a significant improvement compared to the sham group. However, daily pre- and post-intervention measurements showed significant differences in reading and speaking fluency and SSI-IV score on day 3 of the intervention. Although the results of this 5-day study showed that the tDCS did not lead to a significant improvement in speech fluency, it provides some indications that further research is needed. Consideration of these factors may shed light on future studies to determine appropriate tDCS protocols for the treatment of developmental stuttering. Keywords: development stuttering, tDCS, non-invasive brain stimulation, randomized controlled trial, speech therapy