Neuroanatomical Correlates of Childhood Stuttering: MRI Indices of White and Gray Matter Development That Differentiate Persistence Versus Recovery

Localization of stuttering based on causal brain lesions

Stuttering affects approximately 1 in 100 adults and can result in significant communication problems and social anxiety. It most often occurs as a developmental disorder but can also be caused by focal brain damage. These latter cases may lend unique insight into the brain regions causing stuttering. Here, we investigated the neuroanatomical substrate of stuttering using three independent datasets: (i) case reports from the published literature of acquired neurogenic stuttering following stroke (n = 20, 14 males/six females, 16-77 years); (ii) a clinical single study cohort with acquired neurogenic stuttering following stroke (n = 20, 13 males/seven females, 45-87 years); and (iii) adults with persistent developmental stuttering (n = 20, 14 males/six females, 18-43 years). We used the first two datasets and lesion network mapping to test whether lesions causing acquired stuttering map to a common brain network. We then used the third dataset to test whether this lesion-based network was relevant to developmental stuttering. In our literature dataset, we found that lesions causing stuttering occurred in multiple heterogeneous brain regions, but these lesion locations were all functionally connected to a common network centred around the left putamen, including the claustrum, amygdalostriatal transition area and other adjacent areas. This finding was shown to be specific for stuttering (PFWE < 0.05) and reproducible in our independent clinical cohort of patients with stroke-induced stuttering (PFWE < 0.05), resulting in a common acquired stuttering network across both stroke datasets. Within the common acquired stuttering network, we found a significant association between grey matter volume and stuttering impact for adults with persistent developmental stuttering in the left posteroventral putamen, extending into the adjacent claustrum and amygdalostriatal transition area (PFWE < 0.05). We conclude that lesions causing acquired neurogenic stuttering map to a common brain network, centred to the left putamen, claustrum and amygdalostriatal transition area. The association of this lesion-based network with symptom severity in developmental stuttering suggests a shared neuroanatomy across aetiologies.

Lidcombe Program telehealth treatment for children 6-12 years of age: A Phase II trial

BACKGROUND

For children older than 6 years who stutter, there is a gap in clinical research. This is an issue for speech-language pathologists because the tractability of stuttering decreases and the risk of long-term psychological consequences increase with age.

PURPOSE

To report a Phase II trial of a telehealth version of the Lidcombe Program with school-age children.

METHODS

Participants were 37 children who stuttered, 6-12 years of age, from Australia, New Zealand, Hong Kong, and Singapore. Parents were trained by video telehealth how to deliver the Lidcombe Program to their child. Primary and secondary outcomes were stuttering severity and psychosocial functioning measured pre-treatment and at 6 months and 12 months after starting treatment. Parents submitted two 10-minute recordings of their child speaking in conversation, and three measures of anxiety, impact of stuttering, and communication attitude.

RESULTS

Six months after starting treatment, seven children (18.9%) attained Lidcombe Program Stage 2 criteria, 25 children (67.6%) showed a partial response to treatment, and five children (13.5%) showed no response. By 12 months, 12 children (32.4%) had reached Stage 2 criteria. Psychosocial improvements were observed 6 and 12 months after starting treatment.

CONCLUSIONS

The Lidcombe Program may eliminate or nearly eliminate stuttering for about one third of children 6-12 years of age. Randomized controlled trials with this age group involving the Lidcombe Program are warranted. In the interim, the Lidcombe Program is a clinical option clinicians can implement with this age group to reduce stuttering and its psychosocial impacts.

Reduced stuttering for school-age children: A systematic review

BACKGROUND

Treatment of school-age children (6-12 years of age) who stutter is a public health priority. Their clinical needs include a psychosocial focus and stuttering reduction. For the latter clinical need, there is a critical window of opportunity for these children warranting research attention.

PURPOSE

The purpose of the review is to guide future clinical research by establishing (a) what interventions are associated with stuttering reduction for school-age children (b) the reported immediate and longer-term effects of those interventions, and (c) the level of evidence for these interventions in terms of study design.

METHODS

Fourteen databases and three conference proceedings were searched for interventions used to reduce stuttering in school-age children. Primary outcomes were mean stuttering reductions pre-treatment, immediately post-treatment, and any follow-up assessments.

RESULTS

Of the 4305 studies identified from the databases, 67 studies met inclusion criteria. Five different treatment approaches were reported in the literature that might reduce stuttering for a school-age child, but with varying effect sizes. These include (a) operant methods, (b) speech restructuring, (c) combined operant methods and speech restructuring, (d) machine-driven treatments, and (e) treatments with a cognitive behaviour therapy component.

CONCLUSIONS

Operant methods warrant investigation in future clinical trial research, as do variants of speech restructuring. Hybrid approaches showed encouraging results, including speech restructuring variants combined with operant methods or with cognitive behaviour therapy. However, evidence is preliminary only at Phase I and II trials. Several treatments with reported clinical promise have been overlooked for decades and require further investigation.

A comparison of structural morphometry in children and adults with persistent developmental stuttering

This cross-sectional study aimed to differentiate earlier occurring neuroanatomical differences that may reflect core deficits in stuttering versus changes associated with a longer duration of stuttering by analysing structural morphometry in a large sample of children and adults who stutter and age-matched controls. Whole-brain T1-weighted structural scans were obtained from 166 individuals who stutter (74 children, 92 adults; ages 3-58) and 191 controls (92 children, 99 adults; ages 3-53) from eight prior studies in our laboratories. Mean size and gyrification measures were extracted using FreeSurfer software for each cortical region of interest. FreeSurfer software was also used to generate subcortical volumes for regions in the automatic subcortical segmentation. For cortical analyses, separate ANOVA analyses of size (surface area, cortical thickness) and gyrification (local gyrification index) measures were conducted to test for a main effect of diagnosis (stuttering, control) and the interaction of diagnosis-group with age-group (children, adults) across cortical regions. Cortical analyses were first conducted across a set of regions that comprise the speech network and then in a second whole-brain analysis. Next, separate ANOVA analyses of volume were conducted across subcortical regions in each hemisphere. False discovery rate corrections were applied for all analyses. Additionally, we tested for correlations between structural morphometry and stuttering severity. Analyses revealed thinner cortex in children who stutter compared with controls in several key speech-planning regions, with significant correlations between cortical thickness and stuttering severity. These differences in cortical size were not present in adults who stutter, who instead showed reduced gyrification in the right inferior frontal gyrus. Findings suggest that early cortical anomalies in key speech planning regions may be associated with stuttering onset. Persistent stuttering into adulthood may result from network-level dysfunction instead of focal differences in cortical morphometry. Adults who stutter may also have a more heterogeneous neural presentation than children who stutter due to their unique lived experiences.

Differences in implicit motor learning between adults who do and do not stutter

Implicit learning allows us to acquire complex motor skills through repeated exposure to sensory cues and repetition of motor behaviours, without awareness or effort. Implicit learning is also critical to the incremental fine-tuning of the perceptual-motor system. To understand how implicit learning and associated domain-general learning processes may contribute to motor learning differences in people who stutter, we investigated implicit finger-sequencing skills in adults who do (AWS) and do not stutter (ANS) on an Alternating Serial Reaction Time task. Our results demonstrated that, while all participants showed evidence of significant sequence-specific learning in their speed of performance, male AWS were slower and made fewer sequence-specific learning gains than their ANS counterparts. Although there were no learning gains evident in accuracy of performance, AWS performed the implicit learning task more accurately than ANS, overall. These findings may have implications for sex-based differences in the experience of developmental stuttering, for the successful acquisition of complex motor skills during development by individuals who stutter, and for the updating and automatization of speech motor plans during the therapeutic process.

Speech Fluency Improvement in Developmental Stuttering Using Non-invasive Brain Stimulation: Insights From Available Evidence

Developmental stuttering (DS) is a disturbance of the normal rhythm of speech that may be interpreted as very debilitating in the most affected cases. Interventions for DS are historically based on the behavioral modifications of speech patterns (e.g., through speech therapy), which are useful to regain a better speech fluency. However, a great variability in intervention outcomes is normally observed, and no definitive evidence is currently available to resolve stuttering, especially in the case of its persistence in adulthood. In the last few decades, DS has been increasingly considered as a functional disturbance, affecting the correct programming of complex motor sequences such as speech. Compatibly, understanding of the neurophysiological bases of DS has dramatically improved, thanks to neuroimaging, and techniques able to interact with neural tissue functioning [e.g., non-invasive brain stimulation (NIBS)]. In this context, the dysfunctional activity of the cortico-basal-thalamo-cortical networks, as well as the defective patterns of connectivity, seems to play a key role, especially in sensorimotor networks. As a consequence, a direct action on the functionality of "defective" or "impaired" brain circuits may help people who stutter to manage dysfluencies in a better way. This may also "potentiate" available interventions, thus favoring more stable outcomes of speech fluency. Attempts aiming at modulating (and improving) brain functioning of people who stutter, realized by using NIBS, are quickly increasing. Here, we will review these recent advancements being applied to the treatment of DS. Insights will be useful not only to assess whether the speech fluency of people who stutter may be ameliorated by acting directly on brain functioning but also will provide further suggestions about the complex and dynamic pathophysiology of DS, where causal effects and "adaptive''/''maladaptive" compensation mechanisms may be strongly overlapped. In conclusion, this review focuses future research toward more specific, targeted, and effective interventions for DS, based on neuromodulation of brain functioning.

Bilinguals who stutter: A cognitive perspective

PURPOSE

Brain differences, both in structure and executive functioning, have been found in both developmental stuttering and bilingualism. However, the etiology of stuttering remains unknown. The early suggestion that stuttering is a result of brain dysfunction has since received support from various behavioral and neuroimaging studies that have revealed functional and structural brain changes in monolinguals who stutter (MWS). In addition, MWS appear to show deficits in executive control. However, there is a lack of data on bilinguals who stutter (BWS). This literature review is intended to provide an overview of both stuttering and bilingualism as well as synthesize areas of overlap among both lines of research and highlight knowledge gaps in the current literature.

METHODS

A systematic literature review on both stuttering and bilingualism studies was conducted, searching for articles containing "stuttering" and/or "bilingualism" and either "brain", "executive functions", "executive control", "motor control", "cognitive reserve", or "brain reserve" in the PubMed database. Additional studies were found by examining the reference list of studies that met the inclusion criteria.

RESULTS

A total of 148 references that met the criteria for inclusion in this paper were used in the review. A comparison of the impact of stuttering or bilingualism on the brain are discussed.

CONCLUSION

Previous research examining a potential bilingual advantage for BWS is mixed. However, if such an advantage does exist, it appears to offset potential deficits in executive functioning that may be associated with stuttering.

Clinical Characteristics Associated With Stuttering Persistence: A Meta-Analysis

Purpose The purpose of this meta-analytic study was to identify clinical characteristics, defined as child factors that can be assessed by a speech-language pathologist as part of a routine speech-language evaluation that may differentiate children who persist in stuttering from children who eventually recover from stuttering. Clinical characteristics explored included sex, age at onset, family history of stuttering, stuttering frequency and severity, speech-language skills, and temperament. Method Studies were identified through electronic databases, journals, and reference lists of relevant reports (e.g., research articles). Eligible studies followed young children who stutter (i.e., under 6 years old) for at least 24 months, assessed a potential clinical marker at study entry, and determined talker group classification (i.e., persistent or recovered) at study completion. Sex and family history differences were estimated using risk ratios; all other differences were estimated using Hedges's g. Heterogeneity and methodological differences among studies were evaluated. Results Eleven studies (41 reports) met eligibility criteria. Persistent children were older at stuttering onset and exhibited higher frequencies of stuttering-like disfluencies, lower speech sound accuracy, and lower expressive and receptive language skills than recovered children. Males and children with a family history of stuttering were also more likely to persist. Conclusions Clinical characteristics were identified that are associated with increased risk for stuttering persistence. Future studies have the potential to translate these clinical characteristics into prognostic markers for stuttering persistence risk.

Developmental stuttering and the role of the supplementary motor cortex

Developmental stuttering is a frequent neurodevelopmental disorder with a complex neurobiological basis. Robust neural markers of stuttering include imbalanced activity of speech and motor related brain regions, and their impaired structural connectivity. The dynamic interaction of cortical regions is regulated by the cortico-basal ganglia-thalamo-cortical system with the supplementary motor area constituting a crucial cortical site. The SMA integrates information from different neural circuits, and manages information about motor programs such as self-initiated movements, motor sequences, and motor learning. Abnormal functioning of SMA is increasingly reported in stuttering, and has been recently indicated as an additional "neural marker" of DS: anatomical and functional data have documented abnormal structure and activity of the SMA, especially in motor and speech networks. Its connectivity is often impaired, especially when considering networks of the left hemisphere. Compatibly, recent data suggest that, in DS, SMA is part of a poorly synchronized neural network, thus resulting in a likely substrate for the appearance of DS symptoms. However, as evident when considering neural models of stuttering, the role of SMA has not been fully clarified. Herein, the available evidence is reviewed, which highlights the role of the SMA in DS as a neural "hub", receiving and conveying altered information, thus "gating" the release of correct or abnormal motor plans.