Behavioral and Neural Correlates of Speech Motor Sequence Learning in Stuttering and Neurotypical Speakers: An fMRI Investigation

Abstract

Stuttering is a neurodevelopmental disorder characterized by impaired production of coordinated articulatory movements needed for fluent speech. It is currently unknown whether these abnormal production characteristics reflect disruptions to brain mechanisms underlying the acquisition and/or execution of speech motor sequences. To dissociate learning and control processes, we used a motor sequence learning paradigm to examine the behavioral and neural correlates of learning to produce novel phoneme sequences in adults who stutter (AWS) and neurotypical controls. Participants intensively practiced producing pseudowords containing non-native consonant clusters (e.g., “gvasf”) over two days. The behavioral results indicated that although the two experimental groups showed comparable learning trajectories, AWS performed significantly worse on the task prior to and after speech motor practice. Using functional magnetic resonance imaging (fMRI), the authors compared brain activity during articulation of the practiced words and a set of novel pseudowords (matched in phonetic complexity). FMRI analyses revealed no differences between AWS and controls in cortical or subcortical regions; both groups showed comparable increases in activation in left-lateralized brain areas implicated in phonological working memory and speech motor planning during production of the novel sequences compared to the practiced sequences. Moreover, activation in left-lateralized basal ganglia sites was negatively correlated with in-scanner mean disfluency in AWS. Collectively, these findings demonstrate that AWS exhibit no deficit in constructing new speech motor sequences but do show impaired execution of these sequences before and after they have been acquired and consolidated.

Fluency shaping increases integration of the command-to-execution and the auditory-to-motor pathways in persistent developmental stuttering

“…Thus, speech planning processes or the coordination of articulators were not addressed to result in task-free functional connectivity changes. Our observation is in line with a recent neuroimaging study showing that PDS exhibit no deficit in learning to produce novel phoneme sequences (Masapollo et al, 2021); task-related fMRI data showed no difference in brain activity between PDS and controls for the articulation of practiced und novel pseudowords. Thus, sensorimotor learning and feedback processing in the context of voice control may be the main drivers of the neuroplasticity in the current study.…”

Neurocomputational modeling of speech motor development

“…The required number of cortico-cortical connections (black arrows) has decreased substantially, having been replaced by subcortical communications through the cerebellum (green arrows) and basal ganglia (red arrows). Evidence for speech learning-related reductions in processing load has been demonstrated by neuroimaging studies of nonnative consonant cluster learning (Segawa, Tourville, Beal, & Guenther, 2015;Masapollo et al, 2021).…”

The Dopamine System and Automatization of Movement Sequences: A Review With Relevance for Speech and Stuttering

“…In a recent study combining speech motor training of novel phoneme sequences and brain imaging (fMRI), Masapollo et al (2021) found indications that people who stutter do not differ from typically fluent persons in terms of the ability to learn new speech motor sequences, but show impairments in the execution of the learned sequences. In addition, they observed an association between high level of in-scanner speech disfluencies and low activation of left basal ganglia sites.…”