The Effects of tDCS on Speech Fluency in People Who Stutter: A Narrative Review

To improve the outcomes of current treatments for stuttering, researchers have explored adjunct tools such as transcranial Direct Current Stimulation (tDCS). The purpose of this paper is to review the literature investigating the effectiveness of tDCS for people who stutter (PWS) and offer some directions for future research. To achieve the objective of this study, we conducted a narrative review of the existing literature. Articles were selected using these inclusion criteria: participants, tDCS protocol, control group and primary outcomes. Our literature search was limited to studies published in English with no limits on the publication year. We only extracted data from studies that investigated the effects of tDCS on PWS. Systematic reviews, meta-analyses and other forms of reviews regarding tDCS were not included. We identified 101 studies during the exploratory phase. Ultimately, seven studies met our inclusion criteria. Of the included papers, five studies reported mixed effects, one study showed no effect and one study showed positive effects of tDCS. We summarized the studies in terms of several methodological features and the observed effects from tDCS. We also used SimNIBS modelling to compare the effects of different stimulation parameters on brain activity and outcomes. The studies reviewed in this study have reported a variable effectiveness of tDCS for enhancing speech fluency in PWS. As a result, it remains unclear whether tDCS is an effective tool for stuttering intervention, and the optimal stimulation parameters are not yet established. Several suggestions for future research are offered.