The application of rTMS over SMA combined with rhythmic speech training for stuttering intervention

Abstract

<p>Behavioral treatments for adults who stutter (AWS) often involve adopting a speech pattern that improves fluency, such as speaking rhythmically or prolonging speech sounds. However, maintaining the benefits of these treatments is challenging. Recently, brain stimulation techniques, such as transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), have shown potential in enhancing behavioral therapy for people with neurogenic speech and language disorders (Breining & Sebastian, 2020). Non-invasive brain stimulation (NIBS) techniques, including tDCS and TMS, modulate or stimulate neural activities in targeted regions, respectively. These methods have been identified as ways to promote neural plasticity and long-term potentiation (Busan, 2020). </p><p>NIBS methods have been used to explore the neural mechanisms underlying stuttering. For example, earlier studies using direct electrical stimulation over the supplementary motor area (SMA) induced stuttering-like behaviors in typically fluent speakers (Penfield & Welch, 1951). Recently, NIBS has been adopted as an add-on method to enhance speech fluency in people who stutter. It has been shown that the application of multiple sessions of tDCS over different regions, such as the inferior frontal gyrus (IFG) and temporoparietal areas, induces promising effects on reducing speech disfluencies in adults who stutter (Chesters, Möttönen, & Watkins, 2018; Moein et al., 2022) . However, tDCS (unlike TMS) lacks the focality of stimulation and induces more diffuse stimulation across the brain regions, which means the effects may not be fully attributed to the area under the stimulation. There is relatively less evidence on the application of TMS for stuttering intervention. </p><p><br></p><p>This study aimed to examine the effects of excitatory rTMS over the SMA on improving speech fluency and stuttering severity, as measured by primary outcome measures such as %SS, SSI-4, and self-rating. Participants were randomly allocated to different types of treatment, including 30 minutes of active or sham rTMS combined with speech training over five consecutive days in one week. There was a two-week break (washout period) between the two treatment phases, after which participants crossed over to the opposite treatment block.</p><p>While treatment-induced improvements on stuttering severity were observed, the effects were comparable between sham and TMS conditions on connected speech (i.e., reading and speaking tasks). However, the rTMS condition (but not the sham) demonstrated improved fluency in the production of tongue twisters. It is arguable that the lack of significant results in reading and speaking tasks might be due to the lower demands in speech motor planning and production during natural speech as opposed to the production of tongue twisters. Further research is needed to better understand the potential benefits and limitations of neuromodulation methods, especially TMS, in stuttering treatments and to optimize the combined intervention approach. <br></p>