Reactive Inhibitory Control Precedes Overt Stuttering Events

Abstract

Research points to neurofunctional differences underlying fluent speech production in stutterers and non-stutterers. There has been considerably less work focusing on the processes that underlie stuttered speech, primarily due to the difficulty of reliably eliciting stuttering in the unnatural contexts associated with neuroimaging experiments. We used magnetoencephalography (MEG) to test the hypothesis that stuttering events result from global motor inhibition–a “freeze” response typically characterized by increased beta power in nodes of the action-stopping network. We leveraged a novel clinical interview to develop participant-specific stimuli in order to elicit a comparable amount of stuttered and fluent trials. Twenty-nine adult stutterers participated. The paradigm included a cue prior to a go signal, which allowed us to isolate processes associated with stuttered and fluent trials prior to speech initiation. During this pre-speech time window, stuttered trials were associated with greater beta power in the right pre-supplementary motor area, a key node in the action-stopping network, compared to fluent trials. Beta power in the right pre-supplementary area was related to a clinical measure of stuttering severity. We also found that anticipated words identified independently by participants were stuttered more often than those generated by the researchers, which were based on the participants’ reported anticipated sounds. This suggests that global motor inhibition results from stuttering anticipation. This study represents the largest comparison of stuttered and fluent speech to date. The findings provide a foundation for clinical trials that test the efficacy of neuromodulation on stuttering. Moreover, our study demonstrates the feasibility of using our approach for eliciting stuttering during MEG and functional magnetic resonance imaging experiments so that the neurobiological bases of stuttered speech can be further elucidated.

Inhibitory control of speech production in the human premotor frontal cortex

“…In verbal communication where there is a natural, fast exchange of phrases and sentences, inhibitory signals are likely to interlace with excitatory signals with precise timing. In speech impairments such as stuttering, aberrant inhibitory signals may cause the frequent stops found in production (Chang and Guenther, 2020; Eggers et al, 2010; Markett et al, 2016; Neef et al, 2018; Orpella et al, 2022). Investigations into the relationship of stop activity with normal and abnormal speech will be important future directions.…”

“…The control for such stopping requires suppression of planned actions and is thus believed to involve an inhibitory mechanism (Aron, 2007). Deficits in inhibitory functions have been hypothesized to cause impairments in speech and communication such as stuttering (Chang and Guenther, 2020; Eggers et al, 2010; Markett et al, 2016; Neef et al, 2018; Orpella et al, 2022) and excessive self-directed speech in attention deficit hyperactivity disorder (ADHD) (Alderson et al, 2007).…”

Self-reported effects of classic psychedelics on stuttering

“…One possible mechanism could be reduced involvement of cognitive control processes during speech production. Recent work points to overactivation in the cognitive control network of stutterers prior to stuttered vs. fluent speech (Jackson et al, 2022;Orpella et al, 2023). Moreover, internally-versus externallydirected focus is known to disrupt simple or automatized motor movements (Kal et al, 2013;McNevin et al, 2003;Wulf et al, 2001), and there is some evidence that this is the case in stuttering (Eichorn et al, 2016;Jackson et al, 2016).…”

“…Psychedelics have been suggested to reduce the involvement of control processes across a variety of cognitive and perceptual domains (Barrett et al, 2018;Bouso et al, 2013;Quednow et al, 2012;Schmidt et al, 2018;Vollenweider et al, 2007). It could be that psychedelics dampen hyperactivation in these right hemisphere areas, which reduces stuttering or more likely makes it easier to move through stuttering events potentially by limiting interference of cognitive control on the speech-motor system (Alm, 2014;Jackson et al, 2022;Orpella et al, 2023).…”