Functional-lesion investigation of developmental stuttering with positron emission tomography

Stuttering: A Disorder of Energy Supply to Neurons?

Stuttering is a disorder characterized by intermittent loss of volitional control of speech movements. This hypothesis and theory article focuses on the proposal that stuttering may be related to an impairment of the energy supply to neurons. Findings from electroencephalography (EEG), brain imaging, genetics, and biochemistry are reviewed: (1) Analyses of the EEG spectra at rest have repeatedly reported reduced power in the beta band, which is compatible with indications of reduced metabolism. (2) Studies of the absolute level of regional cerebral blood flow (rCBF) show conflicting findings, with two studies reporting reduced rCBF in the frontal lobe, and two studies, based on a different method, reporting no group differences. This contradiction has not yet been resolved. (3) The pattern of reduction in the studies reporting reduced rCBF corresponds to the regional pattern of the glycolytic index (GI; Vaishnavi et al., 2010). High regional GI indicates high reliance on non-oxidative metabolism, i.e., glycolysis. (4) Variants of the gene ARNT2 have been associated with stuttering. This gene is primarily expressed in the brain, with a pattern roughly corresponding to the pattern of regional GI. A central function of the ARNT2 protein is to act as one part of a sensor system indicating low levels of oxygen in brain tissue and to activate appropriate responses, including activation of glycolysis. (5) It has been established that genes related to the functions of the lysosomes are implicated in some cases of stuttering. It is possible that these gene variants result in a reduced peak rate of energy supply to neurons. (6) Lastly, there are indications of interactions between the metabolic system and the dopamine system: for example, it is known that acute hypoxia results in an elevated tonic level of dopamine in the synapses. Will mild chronic limitations of energy supply also result in elevated levels of dopamine? The indications of such interaction effects suggest that the metabolic theory of stuttering should be explored in parallel with the exploration of the dopaminergic theory.

A systematic literature review of neuroimaging research on developmental stuttering between 1995 and 2016

PURPOSE

Stuttering is a disorder that affects millions of people all over the world. Over the past two decades, there has been a great deal of interest in investigating the neural basis of the disorder. This systematic literature review is intended to provide a comprehensive summary of the neuroimaging literature on developmental stuttering. It is a resource for researchers to quickly and easily identify relevant studies for their areas of interest and enable them to determine the most appropriate methodology to utilize in their work. The review also highlights gaps in the literature in terms of methodology and areas of research.

METHODS

We conducted a systematic literature review on neuroimaging studies on developmental stuttering according to the PRISMA guidelines. We searched for articles in the pubmed database containing "stuttering" OR "stammering" AND either "MRI", "PET", "EEG", "MEG", "TMS"or "brain" that were published between 1995/​01/​01 and 2016/​01/​01.

RESULTS

The search returned a total of 359 items with an additional 26 identified from a manual search. Of these, there were a total of 111 full text articles that met criteria for inclusion in the systematic literature review. We also discuss neuroimaging studies on developmental stuttering published throughout 2016. The discussion of the results is organized first by methodology and second by population (i.e., adults or children) and includes tables that contain all items returned by the search.

CONCLUSIONS

There are widespread abnormalities in the structural architecture and functional organization of the brains of adults and children who stutter. These are evident not only in speech tasks, but also non-speech tasks. Future research should make greater use of functional neuroimaging and noninvasive brain stimulation, and employ structural methodologies that have greater sensitivity. Newly planned studies should also investigate sex differences, focus on augmenting treatment, examine moments of dysfluency and longitudinally or cross-sectionally investigate developmental trajectories in stuttering.

Functional neural circuits that underlie developmental stuttering

The aim of this study was to identify differences in functional and effective brain connectivity between persons who stutter (PWS) and typically developing (TD) fluent speakers, and to assess whether those differences can serve as biomarkers to distinguish PWS from TD controls. We acquired resting-state functional magnetic resonance imaging data in 44 PWS and 50 TD controls. We then used Independent Component Analysis (ICA) together with Hierarchical Partner Matching (HPM) to identify networks of robust, functionally connected brain regions that were highly reproducible across participants, and we assessed whether connectivity differed significantly across diagnostic groups. We then used Granger Causality (GC) to study the causal interactions (effective connectivity) between the regions that ICA and HPM identified. Finally, we used a kernel support vector machine to assess how well these measures of functional connectivity and granger causality discriminate PWS from TD controls. Functional connectivity was stronger in PWS compared with TD controls in the supplementary motor area (SMA) and primary motor cortices, but weaker in inferior frontal cortex (IFG, Broca’s area), caudate, putamen, and thalamus. Additionally, causal influences were significantly weaker in PWS from the IFG to SMA, and from the basal ganglia to IFG through the thalamus, compared to TD controls. ICA and GC indices together yielded an accuracy of 92.7% in classifying PWS from TD controls. Our findings suggest the presence of dysfunctional circuits that support speech planning and timing cues for the initiation and execution of motor sequences in PWS. Our high accuracy of classification further suggests that these aberrant brain features may serve as robust biomarkers for PWS.

A review of brain circuitries involved in stuttering

Stuttering has been the subject of much research, nevertheless its etiology remains incompletely understood. This article presents a critical review of the literature on stuttering, with particular reference to the role of the basal ganglia (BG). Neuroimaging and lesion studies of developmental and acquired stuttering, as well as pharmacological and genetic studies are discussed. Evidence of structural and functional changes in the BG in those who stutter indicates that this motor speech disorder is due, at least in part, to abnormal BG cues for the initiation and termination of articulatory movements. Studies discussed provide evidence of a dysfunctional hyperdopaminergic state of the thalamocortical pathways underlying speech motor control in stuttering. Evidence that stuttering can improve, worsen or recur following deep brain stimulation for other indications is presented in order to emphasize the role of BG in stuttering. Further research is needed to fully elucidate the pathophysiology of this speech disorder, which is associated with significant social isolation.

Functional connectivity changes in adults with developmental stuttering: a preliminary study using quantitative electro-encephalography

Introduction: Stuttering is defined as speech characterized by verbal dysfluencies, but should not be seen as an isolated speech disorder, but as a generalized sensorimotor timing deficit due to impaired communication between speech related brain areas. Therefore we focused on resting state brain activity and functional connectivity.

Method: We included 11 patients with developmental stuttering and 11 age matched controls. To objectify stuttering severity and the impact on quality of life (QoL), we used the Dutch validated Test for Stuttering Severity-Readers (TSS-R) and the Overall Assessment of the Speaker’s Experience of Stuttering (OASES), respectively. Furthermore, we used standardized low resolution brain electromagnetic tomography (sLORETA) analyses to look at resting state activity and functional connectivity differences and their correlations with the TSS-R and OASES.

Results: No significant results could be obtained when looking at neural activity, however significant alterations in resting state functional connectivity could be demonstrated between persons who stutter (PWS) and fluently speaking controls, predominantly interhemispheric, i.e., a decreased functional connectivity for high frequency oscillations (beta and gamma) between motor speech areas (BA44 and 45) and the contralateral premotor (BA6) and motor (BA4) areas. Moreover, a positive correlation was found between functional connectivity at low frequency oscillations (theta and alpha) and stuttering severity, while a mixed increased and decreased functional connectivity at low and high frequency oscillations correlated with QoL.

Discussion: PWS are characterized by decreased high frequency interhemispheric functional connectivity between motor speech, premotor and motor areas in the resting state, while higher functional connectivity in the low frequency bands indicates more severe speech disturbances, suggesting that increased interhemispheric and right sided functional connectivity is maladaptive.

Brain activity in adults who stutter: similarities across speaking tasks and correlations with stuttering frequency and speaking rate

Many differences in brain activity have been reported between persons who stutter (PWS) and typically fluent controls during oral reading tasks. An earlier meta-analysis of imaging studies identified stutter-related regions, but recent studies report less agreement with those regions. A PET study on adult dextral PWS (n=18) and matched fluent controls (CONT, n=12) is reported that used both oral reading and monologue tasks. After correcting for speech rate differences between the groups the task-activation differences were surprisingly small. For both analyses only some regions previously considered stutter-related were more activated in the PWS group than in the CONT group, and these were also activated during eyes-closed rest (ECR). In the PWS group, stuttering frequency was correlated with cortico-striatal-thalamic circuit activity in both speaking tasks. The neuroimaging findings for the PWS group, relative to the CONT group, appear consistent with neuroanatomic abnormalities being increasingly reported among PWS.

Resting-state brain activity in adult males who stutter

Although developmental stuttering has been extensively studied with structural and task-based functional magnetic resonance imaging (fMRI), few studies have focused on resting-state brain activity in this disorder. We investigated resting-state brain activity of stuttering subjects by analyzing the amplitude of low-frequency fluctuation (ALFF), region of interest (ROI)-based functional connectivity (FC) and independent component analysis (ICA)-based FC. Forty-four adult males with developmental stuttering and 46 age-matched fluent male controls were scanned using resting-state fMRI. ALFF, ROI-based FCs and ICA-based FCs were compared between male stuttering subjects and fluent controls in a voxel-wise manner. Compared with fluent controls, stuttering subjects showed increased ALFF in left brain areas related to speech motor and auditory functions and bilateral prefrontal cortices related to cognitive control. However, stuttering subjects showed decreased ALFF in the left posterior language reception area and bilateral non-speech motor areas. ROI-based FC analysis revealed decreased FC between the posterior language area involved in the perception and decoding of sensory information and anterior brain area involved in the initiation of speech motor function, as well as increased FC within anterior or posterior speech- and language-associated areas and between the prefrontal areas and default-mode network (DMN) in stuttering subjects. ICA showed that stuttering subjects had decreased FC in the DMN and increased FC in the sensorimotor network. Our findings support the concept that stuttering subjects have deficits in multiple functional systems (motor, language, auditory and DMN) and in the connections between them.

Reprint of: stuttering treatment control using P300 event-related potentials

Positron emission tomography studies during speech have indicated a failure to show the normal activation of auditory cortical areas in stuttering individuals. In the present study, P300 event-related potentials were used to investigate possible effects of behavioral treatment on the pattern of signal amplitude and latency between waves. In order to compare variations in P300 measurements, a control group paired by age and gender to the group of stutterers, was included in the study. Findings suggest that the group of stutterers presented a significant decrease in stuttering severity after the fluency treatment program. Regarding P300 measurements, stutterers and their controls presented results within normal limits in all testing situations and no significant statistical variations between pre and post treatment testing. When comparing individual results between the testing situations, stutterers presented a higher average decrease in wave latency for the right ear following treatment. The results are discussed in light of previous P300 event-related potentials and functional imaging studies with stuttering adults.

EDUCATIONAL OBJECTIVES

The reader will learn about and be able to describe the: (1) use of P300 event-related potentials in the study of stuttering; (2) differences between stuttering and non-stuttering adults; and (3) effects of behavioral fluency treatment on cerebral activity in stuttering speakers.

Stuttering treatment control using P300 event-related potentials

Positron emission tomography studies during speech have indicated a failure to show the normal activation of auditory cortical areas in stuttering individuals. In the present study, P300 event-related potentials were used to investigate possible effects of behavioral treatment on the pattern of signal amplitude and latency between waves. In order to compare variations in P300 measurements, a control group paired by age and gender to the group of stutterers, was included in the study. Findings suggest that the group of stutterers presented a significant decrease in stuttering severity after the fluency treatment program. Regarding P300 measurements, stutterers and their controls presented results within normal limits in all testing situations and no significant statistical variations between pre and post treatment testing. When comparing individual results between the testing situations, stutterers presented a higher average decrease in wave latency for the right ear following treatment. The results are discussed in light of previous P300 event-related potentials and functional imaging studies with stuttering adults.

EDUCATIONAL OBJECTIVES

The reader will learn about and be able to describe the: (1) use of P300 event-related potentials in the study of stuttering; (2) differences between stuttering and non-stuttering adults; and (3) effects of behavioral fluency treatment on cerebral activity in stuttering speakers.

Ethical principles associated with the publication of research in ASHA's scholarly journals: importance and adequacy of coverage

PURPOSE

The purpose of this 2-part study was to determine the importance of specific topics relating to publication ethics and adequacy of the American Speech-Language-Hearing Association's (ASHA's) policies regarding these topics.

METHOD

A 56-item Web-based survey was sent to (a) ASHA journal editors, associate editors, and members of the Publications Board (Group 1); (b) authors, reviewers, and members of ASHA's Board of Ethics (Group 2); and (c) a random sample of the ASHA membership, characterized as journal readers (Group 3). The survey contained 4 questions related to ethical principles associated with the publication of research: (a) In regard to scientific integrity in research publications in general, how important is the issue of [topic]? (b) Should ASHA publication policies address this issue? (c) Do ASHA policies address this issue? (d) If yes, how adequately do ASHA policies address this issue? A second study evaluated the contents of ASHA's publication policy documents in regard to their coverage of the survey topics.

RESULTS

Results indicated many of the topics deemed most important by all groups were included in ASHA's publication policy documents; other topics, although included, were not adequately addressed.

CONCLUSIONS

ASHA needs a single, unifying publication policy document, and increased education of all groups in the realm of ethics in the publication process is indicated.

Potenciais evocados auditivos pré e pós-tratamento em indivíduos gagos: estudo piloto

TEMA: os potenciais auditivos evocados têm sido utilizados como instrumento para determinar o diagnóstico de diversas desordens, assim como para avaliar os resultados de processos terapêuticos. OBJETIVO: investigar a relação entre a melhora da gagueira e a atividade cerebral. MÉTODO: foram investigados os potenciais auditivos evocados pré e pós-tratamento de três indivíduos do sexo masculino, todos com gagueira e idades entre 20 e 31 anos, verificando mudanças na amplitude do sinal e na latência entre ondas. RESULTADOS: os resultados indicam uma correlação positiva entre a redução da porcentagem de sílabas gaguejadas e a melhora na amplitude de onda para a orelha direita. CONCLUSÃO: indivíduos gagos podem exibir diferentes padrões de atividade inter-hemisférica em tarefa com o P300 após serem submetidos a um programa de promoção da fluência.

Asymmetries in mouth opening during word generation in male stuttering and non-stuttering participants

We examined lateral asymmetries in mouth opening in right-handed male stuttering (N = 11) and non-stuttering (N = 14) participants. Lateral asymmetries in mouth opening were video-recorded and analysed in participants while they generated words beginning with the bilabial phones /b, p, m/. Non-stuttering participants showed an expected preference for right mouth opening during the task, whereas a group of stuttering participants who were matched for sex and age produced a left or bilateral pattern of mouth opening. Analysis of variance revealed the difference between the groups to be significant (p < .001). However, there was more variability in the lateral mouth asymmetries in the stuttering participants. We interpret this finding as adding some support for the hypothesis that aberrant hemispheric control for speech is involved in stuttering. Asymmetric mouth openings appear to have no direct linguistic function, and we discuss the possible implications of the phenomenon for models of speech planning and programming.

Right rolandic activation during speech perception in stutterers: a MEG study

The focus of our magnetoencephalographic (MEG) study was to obtain further insight into the neuronal organization of language processing in stutterers. We recorded neuronal activity of 10 male developmental stutterers and 10 male controls, while they listened to pure tones, to words in order to repeat them, and to sentences in order to either repeat or transform them into passive form. Stimulation with pure tones resulted in similar activation patterns in the two groups, but differences emerged in the more complex auditory language tasks. In the stutterers, the left inferior frontal cortex was activated for a short while from 95 to 145 ms after sentence onset, which was not evident in the controls nor in either group during the word task. In both subject groups, the left rolandic area was activated when listening to the speech stimuli, but in the stutterers, there was an additional activation of the right rolandic area from 315 ms onwards, which was more pronounced in the sentence than word task. Activation of areas typically associated with language production was thus observed also during speech perception both in controls and in stutterers. Previous research on speech production in stutterers has found abnormalities in both the amount and timing of activation in these areas. The present data suggest that activation in the left inferior frontal and right rolandic areas in stutterers differs from that in controls also during speech perception.

Using independent component analysis to remove artifact from electroencephalographic measured during stuttered speech

The electro-encephalographic (EEG) activity of people who stutter could provide invaluable information about the association of neural processing and stuttering. However, the EEG has never been adequately studied during speech in which stuttering naturally occurs. This is owing, in part, to the masking of the EEG signal by artifact from sources such as the speech musculature and from ocular activity. The aim of this paper was to demonstrate the ability of independent component analysis (ICA) to remove artifact from the EEG of stuttering children recorded while they are speaking and stuttering. The EEG of 16 male children who stuttered and 16 who did not stutter was recorded during a reading task. The recorded EEG that contained artifact was then subjected to ICA. The results demonstrated that the EEG assessed during stuttered speech had substantially more noise than the EEG of speech that did not contain stuttering (p < 0.01). Furthermore, it was shown that ICA could effectively remove this artifact in all 16 children (p < 0.01). The results from one child highlight the findings that ICA can be used to remove dominant artifact that has prevented the study of EEG activity during stuttered speech in children.

Morphological brain differences between adult stutterers and non-stutterers

Background

The neurophysiological and neuroanatomical foundations of persistent developmental stuttering (PDS) are still a matter of dispute. A main argument is that stutterers show atypical anatomical asymmetries of speech-relevant brain areas, which possibly affect speech fluency. The major aim of this study was to determine whether adults with PDS have anomalous anatomy in cortical speech-language areas.

Methods

Adults with PDS (n = 10) and controls (n = 10) matched for age, sex, hand preference, and education were studied using high-resolution MRI scans. Using a new variant of the voxel-based morphometry technique (augmented VBM) the brains of stutterers and non-stutterers were compared with respect to white matter (WM) and grey matter (GM) differences.

Results

We found increased WM volumes in a right-hemispheric network comprising the superior temporal gyrus (including the planum temporale), the inferior frontal gyrus (including the pars triangularis), the precentral gyrus in the vicinity of the face and mouth representation, and the anterior middle frontal gyrus. In addition, we detected a leftward WM asymmetry in the auditory cortex in non-stutterers, while stutterers showed symmetric WM volumes.

Conclusions

These results provide strong evidence that adults with PDS have anomalous anatomy not only in perisylvian speech and language areas but also in prefrontal and sensorimotor areas. Whether this atypical asymmetry of WM is the cause or the consequence of stuttering is still an unanswered question.

The role of hemispheral asymmetry and regional activity of quantitative EEG in children with stuttering

We investigated the role of delayed cerebral maturation, hemisphere asymmetry and regional differences in children with stuttering and healthy controls during resting state and hyperventilation, using conventional EEG techniques and quantitative EEG (QEEG) analysis. This cross-sectional case control study included 26 children with stuttering and age-sex matched 21 children with no history of stuttering. Visual EEG revealed significantly higher parieto-occipital slow waves and slower fronto-central asynchronic waves in the stutterers than in the controls. QEEG analysis showed significantly increased delta activity, especially in the right frontal and parietal regions and decreased alpha frequency in the bi-frontal regions of the stutterers, compared to the controls. Results are discussed interms of if the maturation hypothesis, especially nondominant frontal lobe (possibly supplementar motor area) and parietal lobe functioning.

fMRI of developmental stuttering: a pilot study

The purpose of this investigation was to explore the feasibility of fMRI in the study of developmental stuttering. Speech contrasts (loud versus silent reading) and language contrasts (reading of semantically meaningful text versus nonsense words) of six developmental stutterers and six nonstutterers were compared using a commercial 1 Tesla MR-Scanner (Siemens Expert). Results indicate that mapping cortical function in persons who stutter is indeed feasible, even with a 1TMR-system. Compared to normals the stutterers seemed to employ different and particularly less differentiated auditory and motor feedback strategies in speech. They apparently rely on auditory processing and on cerebellar contribution as much during silent reading as during reading aloud. Moreover, they showed a greater involvement of the right hemisphere in language processing, activating not only the typical language areas on the left but also and with equal magnitude the right side homologues of these areas. In spite of the promising results, at present several practical problems such as possible movement artifacts and possible masking through scanner noise still hamper a more straightforward use of fMRI in the study of developmental stuttering.

Tics and developmental stuttering

BACKGROUND

Developmental stuttering affects 1% of the population but its cause remains unclear. Recent PET studies of metabolism in the central nervous system suggest that it may be related to dysfunction in the basal ganglia or its connections with regions of the cortex associated with speech and motor control.

OBJECTIVE

To determine the presence and characteristics of involuntary movements (IMs) in people who stutter and to investigate the hypothesis that these movements may be of a very similar nature to the IMs seen in patients with movement disorders due to basal ganglia dysfunction.

METHODS

Sixteen adults with developmental stuttering and 16 controls matched for sex and age were audio-videotaped while freely speaking 300 words in conversation and reading aloud 300 words. The audio data was inspected for dysfluencies and the video data was scrutinised for the presence and characteristics of IMs.

RESULTS

Subjects who stuttered produced more IMs than controls during free speech (354 vs 187, p<0.05) and reading (297 vs 47, p<0.001). Most of the IMs in both groups were tics, with a greater number of both simple and complex motor tics (CMTs) in subjects who stuttered. CMTs were more frequent than simple motor tics in those who stuttered, but not in controls. The combination of repetitive eye blink followed by prolonged eye closure was found exclusively in the stuttering group, as were simple tics consisting of eyebrow raise or jaw movement. Dystonia in the form of blepharospasm was identified in a small number of subjects who stuttered. Choreic movements were not associated with stuttering.

CONCLUSIONS

Developmental stuttering is associated with the presence of IMs that are predominantly simple and CMTs. This association suggests that tics and stuttering may share a common pathophysiology and supports the view that, in common with tics, stuttering may reflect dysfunction in the basal ganglia or its immediate connections.

Relationship between the stuttering severity index and speech rate

CONTEXT

The speech rate is one of the parameters considered when investigating speech fluency and is an important variable in the assessment of individuals with communication complaints.

OBJECTIVE

To correlate the stuttering severity index with one of the indices used for assessing fluency/speech rate.

DESIGN

Cross-sectional study.

SETTING

Fluency and Fluency Disorders Investigation Laboratory, Faculdade de Medicina da Universidade de São Paulo.

PARTICIPANTS

Seventy adults with stuttering diagnosis.

MAIN MEASUREMENTS

A speech sample from each participant containing at least 200 fluent syllables was videotaped and analyzed according to a stuttering severity index test and speech rate parameters.

RESULTS

The results obtained in this study indicate that the stuttering severity and the speech rate present significant variation, i.e., the more severe the stuttering is, the lower the speech rate in words and syllables per minute.

DISCUSSION AND CONCLUSION

The results suggest that speech rate is an important indicator of fluency levels and should be incorporated in the assessment and treatment of stuttering. This study represents a first attempt to identify the possible subtypes of developmental stuttering.

DEFINITION

Objective tests that quantify diseases are important in their diagnosis, treatment and prognosis.

Preliminary results of a functional MRI study of brain activation patterns in stuttering and nonstuttering speakers during a lexical access task

An fMRI study examining lexical access and lexical generation in nine non-stuttering and seven stuttering speakers is presented. Lexical access was examined during a word description task that was presented auditorily while subjects "silently" thought of the target words. Participants alternated between four 30-s rest blocks and four 30-s "active" blocks. Activation patterns were assessed utilizing a standard subtraction paradigm, where the activation during the rest blocks was subtracted from the activation during the active blocks. High levels of variability characterized activation patterns within both speaker groups. Group comparisons using random effects statistical analyses did not identify significant differences between the groups when corrected for multiple comparisons. Analyses were subsequently conducted by comparing the trends in the group activation patterns between the speaker groups using fixed (corrected) and random effects (uncorrected) analyses. Non-stuttering control speakers activated primarily left hemisphere cortical speech and language areas while the stuttering speakers appeared to produce more bilateral activation. Discussion of these results focuses on the specific within- and between-hemispheric activation patterns and possible interpretations of these patterns.

EDUCATIONAL OBJECTIVES

The reader will learn about: (1) issues related to interpreting brain activation findings in stuttering speakers; (2) the role and neurological substrates of lexical access during speech production in non-stuttering and stuttering speakers; (3) the basics of functional MRI; and (4) the brain activation areas involved during a silent lexical retrieval task in non-stuttering and stuttering speakers.

Parkinsonian speech disfluencies: effects of L-dopa-related fluctuations

The excess dopamine theory of stuttering (Wu et al., 1997) contends that stuttering may be related to excess levels of the neurotransmitter dopamine in the brain. As Parkinson's disease (PD) patients commonly exhibit changes in dopamine levels accompanied by changes in motor performance, the present study examined disfluency in PD patients to gain information on the role of dopamine in speech disfluencies. Nine PD patients with no history of developmental stuttering were recorded once before and twice after taking their morning medication (on separate days). They read a passage and produced a monologue. Within-word and overall speech disfluencies were calculated at each recording. Through motor testing, it was inferred that participants had relatively low dopamine levels before taking medication, and relatively high dopamine levels after taking medication. There were no group changes in disfluency levels when the low-dopamine and high-dopamine states were compared. There were, however, significant differences in percent disfluencies between the PD participants and age-matched controls. The results of this study do not strongly support the excess dopamine theory of stuttering. Rather, the disfluency changes exhibited by individual participants support a hypothesis that speech disfluencies may be related to increases or decreases in dopamine levels in the brain.

EDUCATIONAL OBJECTIVES

The reader will learn about: (1). the characteristics of disfluent speech exhibited by speakers with Parkinson's disease. (2). The effect of L-dopa based medications on disfluencies of Parkinsonian speakers. (3). The complex role brain dopamine levels may play in disfluent speaking behavior.

Evidence-based treatment of stuttering: I. Definition and application

The philosophy guiding evidence-based treatment and its application to decision-making in stuttering treatment is described. Limitations to the use of evidence-based treatment principles to guide stuttering treatment, namely the lack of a substantial treatment research literature that can serve as the basis for meta-analyses and systematic reviews of effective treatment studies, are bemoaned. Guidelines are provided to aid clinicians in their own conduct of critical evaluations of treatment research.

EDUCATIONAL OBJECTIVES

The reader will learn about and be able to (1) describe the four steps that characterize evidence-based practice, (2) evaluate previous efforts to develop practice guidelines for stuttering, (3) assess the importance of an evidence-based approach to stuttering treatment, and (4) discuss the need for more research that will contribute to the evidence base.

Visuoperceptual and visuomotor deficits in developmental stutterers: an exploratory study

Although the cause of stuttering is unknown, there is strong evidence for it being a neuromotor disorder characterised by an abnormality of higher control encompassing not only speech but other motor systems. The aim of this exploratory study was to look for the presence of non-speech/language deficits--in particular, visuomotor and visuoperceptual deficits--in persons who stutter. Twelve moderate to severe developmental stutterers were compared with a group of fluent speakers, matched for age and sex, on a range of computerized sensory-motor tasks. These tasks covered various aspects of visuomotor function--ballistic movement, dynamic steadiness, and several types of tracking--and visuoperceptual function--acuity, static perception, and dynamic perception. A novel technique was used to remove the visuospatial component from tracking performance. Stutterers had slower reaction times, less accurate random tracking, and impaired dynamic visual perception. Severity of stuttering correlated with reaction time and dynamic perception. Removal of the visuoperceptual component from tracking performance indicated that the impaired tracking in the stutterers was predominantly due to reduced dynamic perception. This is the first study to provide preliminary evidence for the presence of non-linguistic visuoperceptual and upper-limb visuomotor tracking deficits in people with moderate to severe stuttering. These findings support a neurogenic aetiology for stuttering and are compatible with evidence of an overactive dopamine system in stutterers.

Statistical power in stuttering research: a tutorial

The capacity to make reliable inductive statements about populations is critical for the advancement of scientific knowledge. An important contribution to that advancement of knowledge is determining that effects are either present or not present in populations. Statistical power is an important methodological qualification for any research that presents statistical results, and particularly so for research that presents null results. In this paper we describe the statistical concept of power, outline parameters of research that influence it, and demonstrate how it is calculated. With reference to selected published research, attention is drawn to the problems associated with a body of underpowered research, one being that population effects may go undetected. One way to prevent this problem is to calculate power a priori in planning research and include confidence intervals when presenting the results of research. However, it is difficult, if not impossible in many cases, to obtain high participant numbers for communication disorders of low prevalence such as stuttering. With this in mind, the paper concludes with an attempt to open discussion about ways to redress the problems associated with statistical power.

Brain imaging studies of developmental stuttering

This paper reviews recent brain imaging research on stuttering against a background of studies that the writer and colleagues have been conducting at the University of Texas Health Science Center in San Antonio. The paper begins by reviewing some pertinent background to recent neuroimaging investigations of developmental stuttering. It then outlines the findings from four brain imaging studies that the San Antonio group has conducted using H2(15)O positron emission tomography (PET). Finally, some of the principal findings that are emerging across brain imaging studies of stuttering are reviewed, while also highlighting--and attempting to resolve--some apparent across-study inconsistencies among the findings. Research on stuttering using magnetoencephalogaphy (MEG) and transcranial magnetic stimulation (TMS) is also considered. The findings increasingly point to a failure of normal temporal lobe activation during speech that may either contribute to (or is the result of) a breakdown in the sequencing of processing among premotor regions implicated in phonologic planning.

LEARNING OUTCOMES

As a result of this activity, the participant will become familiar with some recent neurophysiological correlates of stuttering and what they suggest about the nature of this disorder.

Dysfluency and involuntary movements: a new look at developmental stuttering

Studies using modern imaging techniques suggest that, in developmental stuttering, there is dysfunction within the cortical and subcortical areas of the motor control system wider than that pertaining to speech motor control alone. If this is the case, one might expect motor deficits extending beyond and unrelated to the production of speech in people who stutter. This study explored this proposal by investigating the presence and characteristics of involuntary movements accompanying stuttering. Sixteen adults with developmental stuttering and 16 controls matched for age and sex were audio-videotaped during 5 minutes of conversational speech and reading a passage of 350 words. Audio-data were examined for dysfluencies. Movements of the face, head and upper body considered involuntary and not part of normal facial expression or gesture and not part of the mechanics of speech were identified and described from muted video-data. Subjects who stuttered had a higher proportion of classic (within-word) dysfluencies accompanied by involuntary movements (IMs) than controls during speech (24.4% vs. 4.5%, p = .054) and reading (28.6% vs. 4.9%, p = .033). There was no difference in proportion of classic dysfluencies accompanied by IMs between speech and reading for either group. IMs were also seen in both groups during fluent speech, with a similar incidence during free speech (3.9% vs. 3.0%, NS) but a greater incidence in the subjects who stuttered during reading (2.4% vs. 0.8%, p = .03). In contrast, there was no difference between the two groups for IMs accompanying normal (between-word) dysfluencies. This suggests that classic and normal dysfluency and their accompanying IMs have different etiologies. The notion that stuttering and IMs are due to altered function in a motor control system wider than that of speech motor control alone is supported by a higher incidence of IMs in people who stutter during both classic dysfluencies and fluent speech.

Is overt stuttered speech a prerequisite for the neural activations associated with chronic developmental stuttering?

Four adult right-handed chronic stutterers and four age-matched controls completed H(2)(15)O PET scans involving overt and imagined oral reading tasks. During overt stuttered speech prominent activations occurred in SMA (medial), BA 46 (right), anterior insula (bilateral), and cerebellum (bilateral) plus deactivations in right A2 (BA 21/22). These activations and deactivations also occurred when the same stutterers imagined they were stuttering. Some parietal regions were significantly activated during imagined stuttering, but not during overt stuttering. Most regional activations changed in the same direction when overt stuttering ceased (during chorus reading) and when subjects imagined that they were not stuttering (also during chorus reading). Controls displayed fewer similarities between regional activations and deactivations during actual and imagined oral reading. Thus overt stuttering appears not to be a prerequisite for the prominent regional activations and deactivations associated with stuttering.

A positron emission tomography study of silent and oral single word reading in stuttering and nonstuttering adults

Over the last decade positron emission tomography (PET) has been used extensively for the study of language and other cognitive and sensorimotor processes in healthy and diseased individuals. In the present study, [15O]H2O PET scanning was used to investigate the lateralization and functional distribution of cortical and subcortical activity involved in single word reading in stuttering and nonstuttering individuals. Ten right-handed male stuttering adults and matched nonstuttering individuals were instructed to read individually presented single words either silently or out loud. Subtraction of functional brain images obtained during each of the two reading tasks, and during a non-linguistic baseline task, was used to calculate within-group and between-group differences in regional cerebral blood flow by means of statistical parametric mapping. Increased activation in the left anterior cingulate cortex (ACC) was observed during silent reading in the stuttering speakers but not in the nonstuttering group. Because of the hypothesized role of the ACC in selective attention and covert articulatory practice, it is suggested that the observed increased ACC activation in the stuttering individuals reflects the presence of cognitive anticipatory reactions related to stuttering. During the oral reading task, within-group comparisons showed bilateral cortical and subcortical activation in both the stuttering and the nonstuttering speakers. Between-group comparisons showed a proportionally greater left hemisphere activation in the nonstuttering speakers, and a proportionally greater right hemisphere activation in the stuttering individuals. The results of the present study provide qualified support for the hypothesis that stuttering adults show atypical lateralization of language processes.

Stuttering: neuropsychiatric features measured by content analysis of speech and the effect of risperidone on stuttering severity

Positron-emission tomographic (PET) studies and genetic research of stuttering have recently revealed underlying cerebral neurobiologic contributing factors in this disorder. We aimed to assess whether cognitive impairment and other neuropsychiatric dimensions could be detected through computerized content analysis of short samples of speech from stutterers, and whether administration of risperidone in a double-blind placebo-controlled study could decrease the severity of stuttering, as well as any of the neuropsychiatric features of these stutterers. A group of 21 stutterers with the developmental form of stuttering, an onset before age of 6 years, aged 20 to 74 years, and who were otherwise free of major medical or psychiatric problems, initially gave a 5-minute tape-recorded speech sample in response to purposely ambiguous instructions to talk about any interesting or dramatic life experiences. Then, half of these subjects (n = 10) were randomly selected to receive 6 weeks of risperidone treatment up to 2.0 mg/d and the other half (n = 11) were administered a placebo. Both groups of subjects gave a second verbal sample after 6 weeks of treatment. Significantly elevated cognitive impairment and social alienation-personal disorganization scores, derived from the computerized content of the initial 5-minute speech samples, were found. After 6 weeks, the risperidone group improved significantly on a measure of severity of stuttering but did not improve on the percentage of time spent stuttering. The placebo group did not improve on either measure of stuttering. The psychopathological processes of subjects who received risperidone treatment, including those with elevated cognitive impairment and social alienation-personal disorganization, did not change significantly. However, stutterers who had lower scores on verbal content analysis-derived shame anxiety, guilt anxiety, or hostility inward measures improved significantly more with risperidone than stutterers with higher scores on these measures. The findings of elevated cognitive impairment and social alienation-personal disorganization scores of adult stutterers with the early developmental form of stuttering are consistent with the neurobiologic abnormalities found in PET-scan and genetic research involving stutterers. Risperidone (< or =2.0 mg/d) can reduce the severity of stuttering while not significantly affecting the magnitude of neuropsychiatric dimensions such as cognitive impairment or social alienation-personal disorganization. The less the inward shame, guilt, or hostility of the stutterers, the better the beneficial effect of risperidone on the severity of stuttering.

Stuttering children and the probability of remission--the role of cerebral dominance and speech production

OBJECTIVE

The identification of critical characteristics which might predict whether childhood stuttering will become chronic. Part of the study investigates the relationship between hearing and central processing of acoustic stimuli, cerebral dominance and the clinical course of the stuttering.

METHODS

A prospective study of 79 stuttering children aged 3-9 years. The subjects were examined with regard to their cerebral dominance in various tests of laterality, their peripheral hearing and their ability to discriminate sound using the dichotic discrimination test according to Uttenweiler (V. Uttenweiler, Dichotischer Diskriminationstest für Kinder, Sprache Stimme Gehör 4 (1980) 107-111). Results were correlated with the probability of remission of stuttering. Comparisons were made with a control group of 18 children of kindergarten age with normal speech. The period of investigation was 18 months.

RESULTS

Seventy-two children underwent follow-up examinations. Of these, 36 achieved fluency of speech. The results of the dichotic discrimination test showed no relation to the rate of remission. When the relationship between handedness and stuttering was investigated, it was found that left-handed children had a significantly poorer chance of attaining speech fluency.

CONCLUSIONS

The Uttenweiler test allowed no prognostic evaluation of the future course of stuttering in the age group studied, though auditory dominance was not completely developed in a majority of the 3-6 year-old children. Handedness, however, appears to be related to the probability that stuttering will become chronic.

P300 event-related potentials in stutterers and nonstutterers

This study investigated possible differences between adult stutterers and nonstutterers in the P300 event-related potential. Responses to tonal stimuli were recorded from electrodes placed over the left (C3) and righ (C4) hemispheres. The two groups exhibited different patterns of interhemispheric activity. Although all 8 participants in the fluent group exhibited P300s that were higher in amplitude over the right hemisphere, 5 of the 8 disfluent participants had higher amplitude activity over the left hemisphere. These results provide evidence that stutterers and nonstutterers may exhibit differences between hemispheres in the processing of some types of nonlinguistic (tonal) stimuli.