P281 The neurophysiological mechanisms linking stuttering and normal speech

Abstract

Objectives This study examined underlying neurophysiological mechanisms of developmental stuttering – facilitation in the motor cortex during speech preparation served as analogue to the speech planning process. Methods Transcranial Magnetic Stimulation pulses induced Motor Evoked Potentials (MEPs), recorded from the tongue. 18 Adults Who Stutter (AWS) and 17 Adults who do Not Stutter (ANS) completed three experiments: spontaneous speech, planned speech and speech with predefined pacing. Each experiment involved 120 trials. In each trial, participants read a German prefix + verb utterance from a screen; the pulse was applied shortly before speech onset. Trial MEPs were normalised to average non-speech MEPs. MEP amplitude, MEP facilitation ratio (amplitude:pre-speech offset) and group difference were analysed by multiple regression, and speech reaction time analysed by correlation. Results MEP base values were 11.1–23.4% lower in AWS than ANS (by standardised Beta), across all three experiments. MEP facilitation ratio slopes were also 4.9–18.3% smaller in AWS than ANS across all three experiments. Reaction times for AWS were only significantly slower than ANS in the spontaneous speech and predefined pacing experiments. No stuttering was detected during the trials. The group difference in spontaneous speech was 100% and 101% greater than the other two experiments respectively. Discussion While both performance of ANS and AWS worsens under disturbed speech conditions, AWS responded better than controls to greater disturbance. Conclusions Research and therapy in stuttering should focus on non-disturbed speech. Significance These findings give insight into both fluent and dysfluent speech planning, especially in the context of fluency therapies.