Stuttering presents a fascinating paradox: fluent in thought, yet disruptions in speech. Even more intriguing, people who stutter (PWS) may articulate complex ideas with complete fluency when there is no communicative intent, still may struggle to say their own name in public. My research examines the stuttering phenomenon in two stages: first, using functional MRI (fMRI) to find differences in brain activity associated with stuttering, and second, developing innovative techniques to provide options for people who want to work on their fluency.

In my first study, we examined brain activity differences between PWS and controls using data from four previous fMRI studies involving sentence repetition (109 participants in total). Despite this relatively large sample size, we found no significant group differences at a strict statistical threshold (Z > 3.1). However, a lower uncorrected threshold revealed results consistent with earlier meta-analyses, such as overactivity in the right anterior insular cortex, while our novel finding was the bilateral overactivation in the red nucleus of PWS. In the second study, we investigated the incomplete cerebral dominance theory by analysing data from the same fMRI studies in four different speech and language tasks. Our findings showed no support for this theory since language lateralisation did not differ between PWS and controls.

In the second part of my thesis, we evaluated the effectiveness of theta-gamma peak transcranial alternating current stimulation to enhance sensorimotor learning of speech in typically fluent speakers. While this protocol did not significantly impact speech adaptation in the learning phase, exploratory analysis suggested potential benefits in retaining the learned state during the after-effect phase. The final study introduced a creative use of choral speech (speaking in unison with another voice) to eliminate stuttering during presentations. The method led to a major drop in disfluent syllables, from 10% to below 3% on average, a level considered clinical threshold.

In the general discussion, I proposed a unified theory of stuttering that considers both neural and psychological correlates, along with future studies to develop interventions with the ultimate goal of enhancing speech fluency and reducing social anxiety in PWS.