Differences in dynamic motor selection in stuttering

Stuttering involves interruptions to the smooth flow of speech occurring mostly at syllable onset. Speech fluency is enhanced in people who stutter (PWS) by external timing cues. This has been taken to indicate that difficulties in the temporal organisation of action selection and initiation during speech contribute to stuttering. An important unanswered question is whether putative temporal coordination difficulties are specific to speech or generalize to other actions. Here, we examined the temporal organisation of hand action selection in PWS. Twenty PWS and twenty typically fluent speakers (TFS) underwent magnetoencephalography (MEG) recording while performing a visuomotor working-memory task that encouraged temporally specific selection, preparation and shifts between hand actions. Lateralised sensorimotor mu/beta-frequency (8-30 Hz) activity modulation accompanying hand-action prioritisation was weaker in PWS than TFS. Strikingly, this effect was specific to a period of high uncertainty regarding which action to select and when. Despite these differences, behavioural performance was well matched between PWS and TFS, and sensorimotor mu/beta activity was functionally relevant for task performance in both groups. The findings suggest a general disruption of temporal structuring of action selection and preparation in stuttering.