Differences in dynamic motor selection in stuttering

Stuttering involves interruptions to the smooth flow of speech occurring mostly at syllable onset.¹ Speech fluency is enhanced in people who stutter (PWS) by external timing cues.² This has been taken to indicate that difficulties in the temporal organization of action selection and initiation during speech contribute to stuttering.³ An important unanswered question is whether putative temporal coordination difficulties are specific to speech or generalize to other actions. Here, we examined the temporal organization 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. Lateralized sensorimotor mu/beta-frequency (8-30 Hz) activity modulation accompanying hand-action prioritization 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, lateralized mu/beta modulation was functionally related to reaction times in both groups and reaction times were well matched between PWS and TFS. The findings suggest a general disruption of temporal structuring of action selection and preparation in stuttering.