An fMRI study of initiation and inhibition of manual responses in people who stutter

Abstract

Developmental stuttering is a speech motor disorder characterised by difficulties initiating speech and frequent interruptions to the speech flow. Previous work suggests that people who stutter (PWS) have an overactive response suppression mechanism. Imaging studies of speech production in PWS consistently reveal greater activity of the right inferior frontal cortex, an area robustly implicated in inhibitory control of both manual and spoken responses. Here, we used a manual response version of the stop-signal task during fMRI to investigate neural differences related to response initiation and inhibition in PWS. Behaviourally, PWS were slower to respond to 'go' stimuli than people who are typically fluent (PWTF), but there was no difference in stop-signal reaction time. Our fMRI results were consistent with these behavioural results. The fMRI analysis revealed the expected networks associated with manual response initiation and inhibition in both groups. However, all contrasts between the two groups were characterised by overactivity in PWS relative to PWTF. This overactivity was significantly different for the initiation of responses (i.e. the 'go' trials) but not for response inhibition (i.e. the 'stop' trials). One explanation of these results is that PWS are consistently in a heightened inhibition state, i.e. areas of the inhibition network are more active, generally. This interpretation is consistent with predictions from the global response suppression hypothesis.

Why Stuttering Occurs

“…Consistent with the account presented here, other researchers have associated this right hemisphere activation during stuttering with activation of the IFG-STN hyperdirect pathway (Arenas, 2017; Neef et al, 2018). Adults who stutter are not impaired in their ability to inhibit verbal responses (Treleaven & Coalson, 2021), but may exhibit widespread hyperactivity across neural correlates of inhibitory control (Wiltshire et al, 2020). This hyperactivity of inhibitory control in adults who stutter may explain previous findings of faster response times compared to those of fluent controls during cognitive conflict (Subramanian & Yairi, 2006).…”