New research: An fMRI study of initiation and inhibition of manual and spoken responses in people who stutter (2025)

New research: An fMRI study of initiation and inhibition of manual and spoken responses in people who stutter (2025) Research link: [https://direct.mit.edu/imag/article/doi/10.1162/IMAG.a.89/131627](https://direct.mit.edu/imag/article/doi/10.1162/IMAG.a.89/131627) **Abstract:** Stuttering is characterised by difficulties initiating speech and frequent interruptions to the flow of speech. Neuroimaging studies of speech production in people who stutter consistently reveal greater activity of the right inferior frontal cortex, an area robustly implicated in stopping manual and spoken responses. This has been linked to an “overactive response suppression mechanism” in people who stutter. Here, we used fMRI to investigate neural differences related to response initiation and inhibition in people who stutter and matched controls (aged 19–45) during performance of the stop-signal task in both the manual and speech domains. We hypothesised there would be increased activity in an inhibitory network centred on the right inferior frontal cortex. Out-of-scanner behavioural testing revealed that people who stutter were slower than controls to respond to ‘go’ stimuli in both the manual and the speech domains, but the groups did not differ in their stop-signal reaction times in either domain. During the fMRI task, both groups activated the expected networks for the manual and speech tasks. Contrary to our hypothesis, we did not observe differences in task-evoked activity between people who stutter and controls during either ‘go’ or ‘stop’ trials. Targeted region-of-interest analyses in the inferior frontal cortex, the supplementary motor area, and the putamen bilaterally confirmed that there were no group differences in activity. These results focus on tasks involving button presses and production of single nonwords, and therefore do not preclude inhibitory involvement related specifically to stuttering events. Our findings indicate that people who stutter do not show behavioural or neural differences in response inhibition, when making simple manual responses and producing fluent speech, contrary to predictions from the global inhibition hypothesis. **Author's interpretation:** * “This suggests that differences between the two groups lie in initiating a response rather than inhibiting an ongoing response and that this effect is more evident in the speech domain compared with the manual domain.” * “Taken together, these results show subtle differences in initiating a response (behaviourally), but no differences either behaviourally or neurally between people who stutter and controls for response inhibition.” * “We find no evidence in support of the idea that people who stutter have an overactive response inhibition mechanism.” * “Our results indicate that while people who stutter were slower to initiate a response (go reaction time) for both conditions, the stopping response (SSRT) was not different to that of controls.” * “Our findings indicate that people who stutter do not differ in the time it takes to inhibit a response in either the manual or speech domains.” * “One explanation is that people who stutter have greater difficulty enacting a response under temporal uncertainty.” * **“Therefore, this result is in accordance with previous work on temporal uncertainty difficulties in people who stutter and may be the result of an impairment in internal cueing, rather than a difference in higher-order cognitive control of responses.”** * “Visually, the group of people who stutter had more spatially extensive task-evoked activation compared with the control group during both ‘Go’ and ‘Stop’ trials, which could reflect greater variability in regions recruited to this task in the stuttering group, which was larger than the control group.” * “In sum, we find little evidence in support of differences between people who stutter and controls in terms of their brain activity when performing either a manual or a speech response to a cue, despite the behavioural finding of slower response initiation (‘Go’ reaction time).” * “The lack of statistical difference between the groups during ‘stop’ trials suggests no difference in activation of brain areas involved in inhibitory control between people who stutter and controls.” * **Limitations: “These results may suggest that the error studied in this paradigm (i.e. a response error) differs from the more subtle error detection involved in matching feedforward and feedback information during speech and stuttering.”** * “Our results find no evidence for a domain general difference in inhibitory responses in people who stutter, **however we did not investigate connected speech or moments of stuttering (a state effect).**” * “This result is in accord with our behavioural results which showed slower reaction times for people who stutter during the speech task.” * “Taken together across modalities, our behavioural results indicate the people who stutter show differences relative to controls in initiating a response, but not stopping a response but our imaging results indicate no differences in brain activity during these two different processes.”