White matter tract strength correlates with therapy outcome in persistent developmental stuttering.

Persistent stuttering is a prevalent neurodevelopmental speech disorder, which presents with involuntary speech blocks, sound and syllable repetitions, and sound prolongations. Affected individuals often struggle with negative feelings, elevated anxiety, and low self-esteem. Neuroimaging studies frequently link persistent stuttering with cortical alterations and dysfunctional cortico-basal ganglia-thalamocortical loops; dMRI data also point toward connectivity changes of the superior longitudinal fasciculus (SLF) and the frontal aslant tract (FAT). Both tracts are involved in speech and language functions, and the FAT also supports inhibitory control and conflict monitoring. Whether the two tracts are involved in therapy-associated improvements and how they relate to therapeutic outcomes is currently unknown. Here, we analyzed dMRI data of 22 patients who participated in a fluency-shaping program, 18 patients not participating in therapy, and 27 fluent control participants, measured 1 year apart. We used diffusion tractography to segment the SLF and FAT bilaterally and to quantify their microstructural properties before and after a fluency-shaping program. Participants learned to speak with soft articulation, pitch, and voicing during a 2-week on-site boot camp and computer-assisted biofeedback-based daily training for 1 year. Therapy had no impact on the microstructural properties of the two tracts. Yet, after therapy, stuttering severity correlated positively with left SLF fractional anisotropy, whereas relief from the social-emotional burden to stutter correlated negatively with right FAT fractional anisotropy. Thus, posttreatment, speech motor performance relates to the left dorsal stream, while the experience of the adverse impact of stuttering relates to the structure recently associated with conflict monitoring and action inhibition.

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

Fluency-shaping enhances the speech fluency of persons who stutter, yet underlying conditions and neuroplasticity-related mechanisms are largely unknown. While speech production-related brain activity in stuttering is well studied, it is unclear whether therapy repairs networks of altered sensorimotor integration, imprecise neural timing and sequencing, faulty error monitoring, or insufficient speech planning. Here, we tested the impact of one-year fluency-shaping therapy on resting-state fMRI connectivity within sets of brain regions subserving these speech functions. We analyzed resting-state data of 22 patients who participated in a fluency-shaping program, 18 patients not participating in therapy, and 28 fluent control participants, measured one year apart. Improved fluency was accompanied by an increased connectivity within the sensorimotor integration network. Specifically, two connections were strengthened; the left inferior frontal gyrus showed increased connectivity with the precentral gyrus at the representation of the left laryngeal motor cortex, and the left inferior frontal gyrus showed increased connectivity with the right superior temporal gyrus. Thus, therapy-associated neural remediation was based on a strengthened integration of the command-to-execution pathway together with an increased auditory-to-motor coupling. Since we investigated task-free brain activity, we assume that our findings are not biased to network activity involved in compensation but represent long-term focal neuroplasticity effects.

Speech restructuring group treatment for 6-to-9-year-old children who stutter: A therapeutic trial.

For children who stutter (CWS), there is good evidence of the benefits of treatment for pre-school age, but an evidence gap for elementary school age. Here we report on the effectiveness of a fluency shaping treatment for 6- to 9-year-old children. The main treatment component is the reinforcement of soft voice onsets. An intensive in-patient group treatment phase lasts 6 days, followed by a 6-month maintenance phase with 3 in-patient weekend group refresher courses. Child and a parent participate together in various treatment activities. In this controlled intervention study (waitlist control, intention-to-treat design) assessments were performed before treatment (T1), 4 weeks after the intensive phase (T2), at the end of the maintenance phase (T3), and 1 year later (T4). Participants were 119 children (108 boys, 11 girls, age 5.5­10.4 years). Control conditions included a subgroup with delayed treatment (N=25) as well as the assessment of complexity of utterances, inter-rater reliability, and speech naturalness. From before treatment to 1-year follow-up, percent stuttered syllables and OASES-S (Overall Assessment of the Speaker's Experience with Stuttering - School-age) scores decreased with large effect size. Speech naturalness improved during this period but did not reach the level of non-stuttering children. Complexity of utterances increased during the intensive phase, but only temporarily. Twenty children (16.8 %, including dropouts) showed no demonstrable treatment benefit. Fluency shaping treatment can be effectively applied to young school children. It is assumed that parental support, group therapy, intensive treatment, and regular exercises at home are essential.

Enlarged Area of Mesencephalic Iron Deposits in Adults Who Stutter.

PURPOSE: Childhood onset speech fluency disorder (stuttering) is possibly related to dopaminergic dysfunction. Mesencephalic hyperechogenicity (ME) detected by transcranial ultrasound (TCS) might be seen as an indirect marker of dopaminergic dysfunction. We here determined whether adults who stutter since childhood (AWS) show ME. METHODS: We performed TCS in ten AWS and ten matched adults who never stuttered. We also assessed motor performance in finger tapping and in the 25 Foot Walking test. RESULTS: Compared to controls, AWS showed enlarged ME on either side. Finger tapping was slower in AWS. Walking cadence, i.e., the ratio of number of steps by time, tended to be higher in AWS than in control participants. DISCUSSION: The results demonstrate a motor deficit in AWS linked to dopaminergic dysfunction and extending beyond speech. Since iron deposits evolve in childhood and shrink thereafter, ME might serve as an easily quantifiable biomarker helping to predict the risk of persistency in children who stutter.

Hand Motor Cortex Excitability During Speaking in Persistent Developmental Stuttering.

Persistent developmental stuttering (PDS) is a speech fluency disorder characterized by intermittent involuntary breakdowns of speech motor control, possibly related to motor cortex excitability. Whether motor cortex dysfunction extends into hand representations is unclear. We here studied task-dependent modulations of hand motor cortex excitability in 10 right-handed adults who stutter (AWS) and 13 age- and sex-matched fluent speaking control participants (ANS), covering a wide range of tasks in an exploratory study. Before, during and after a null speech/rest task, spontaneous speech, solo reading, chorus reading, singing, and non-verbal orofacial movements, transcranial magnetic stimulation was applied over the primary motor cortex and motor evoked potentials (MEPs) were recorded from the abductor digiti minimi muscle of either hand. In both groups, motor threshold was lower in the left than in the right motor cortex. During task performance, MEP amplitudes increased in both groups. A post hoc comparison of spontaneous speech and non-verbal orofacial movements yielded an interaction of group by task with AWS showing larger than ANS MEP amplitude increase in spontaneous speech, but a smaller than ANS MEP amplitude increase in non-verbal orofacial movements. We conclude that hemispheric specialization of hand motor representation is similar for both groups. Spontaneous speech as well as non-verbal orofacial movements are the orofacial tasks that merit further study. The excessive motor cortex facilitation could be reflecting a stronger activation of non-speech muscles during AWS's speech.

No Evidence for Dystonia-Like Sensory Overflow of Tongue Representations in Adults Who Stutter.

Persistent developmental stuttering (PDS) disrupts speech fluency in about 1% of adults. Although many models of speech production assume an intact sensory feedback from the speech organs to the brain, very little is actually known about the integrity of their sensory representation in PDS. Here, we studied somatosensory evoked potentials (SEPs) in adults who stutter (AWS), with the aim of probing the integrity of sensory pathways. In addition, we tested the processing of dual sensory input to address a putative link between stuttering and focal dystonia. In 15 AWS (aged 15-55 years; three females) and 14 matched fluent speaking adults (ANS), we recorded SEPs at C5' and C6' induced by stimulating separately or simultaneously the tongue or the cheek at the corner of the mouth. We determined latencies (N13, P19, and N27) and peak-to-peak amplitudes (N13-P19, P19-N27). We divided amplitudes from simultaneous stimulation by the sum of those from separate stimulation. Amplitude ratios did not differ between groups, indicating normal processing of dual sensory input. This does not support a clinical analogy between focal dystonia and persistent stuttering. SEP latencies as a measure of transmission speed in sensory pathways were significantly shorter in stuttering subjects than in fluent speaking participants, however, this might have been related to a trend for a height difference between groups, and was not confirmed in a replication dataset. In summary, we did not find evidence for dystonia-like sensory overflow of tongue representations in AWS.

Adults who stutter lack the specialised pre-speech facilitation found in non-stutterers.

OBJECTIVES: Persistent developmental stuttering is a speech fluency disorder defined by its symptoms, where the underlying neurophysiological causes remain uncertain. This study examined the underlying neurophysiological mechanisms of the speech planning process, using facilitation in the motor cortex during speech preparation as an analogue. METHODS: transcranial magnetic stimulation (TMS) pulses induced motor evoked potentials (MEPs), which were recorded from the tongue. Eighteen adults who stutter (AWS) and 17 adults who do not stutter (ANS) completed three experiments, which involved reading a German prefix+verb utterance from a screen. Each experiment involved 120 trials with three distinct levels of speech production: immediate speech, delayed speech without pacing and delayed speech with predefined pacing. TMS was applied shortly before speech onset. Trial MEPs were normalised to average non-speech MEPs. MEP amplitude, MEP facilitation ratio (amplitude: pre-speech offset) and group difference were the outcomes of interest analysed by multiple regression, as well as speech reaction time analysed by correlation. RESULTS: MEP values were 11·1%-23·4% lower in AWS than ANS (by standardised Beta), across all three experiments. MEP facilitation ratio slopes were also 4·9%-18·3% flatter in AWS than ANS across all three experiments. Reaction times for AWS were only significantly slower than for ANS in immediate speech and predefined pacing experiments. No stuttering was detected during the trials. The group difference in immediate speech was 100% and 101% greater than the other two experiments respectively. DISCUSSION: While performance of both ANS and AWS worsens under disturbed speech conditions, greater disturbance conditions affected controls worse than AWS. Future research and therapy in stuttering should focus on non-disturbed speech.

Assisted and unassisted recession of functional anomalies associated with dysprosody in adults who stutter.

PURPOSE: Speech in persons who stutter (PWS) is associated with disturbed prosody (speech melody and intonation), which may impact communication. The neural correlates of PWS' altered prosody during speaking are not known, neither is how a speech-restructuring therapy affects prosody at both a behavioral and a cerebral level. METHODS: In this fMRI study, we explored group differences in brain activation associated with the production of different kinds of prosody in 13 male adults who stutter (AWS) before, directly after, and at least 1 year after an effective intensive fluency-shaping treatment, in 13 typically fluent-speaking control participants (CP), and in 13 males who had spontaneously recovered from stuttering during adulthood (RAWS), while sentences were read aloud with 'neutral', instructed emotional (happy), and linguistically driven (questioning) prosody. These activations were related to speech production acoustics. RESULTS: During pre-treatment prosody generation, the pars orbitalis of the left inferior frontal gyrus and the left anterior insula were activated less in AWS than in CP. The degree of hypo-activation correlated with acoustic measures of dysprosody. Paralleling the near-normalization of free speech melody following fluency-shaping therapy, AWS normalized the inferior frontal hypo-activation, sooner after treatment for generating emotional than linguistic prosody. Unassisted recovery was associated with an additional recruitment of cerebellar resources. CONCLUSIONS: Fluency shaping therapy may restructure prosody, which approaches that of typically fluent-speaking people. Such a process may benefit from additional training of instructed emotional and linguistic prosody by inducing plasticity in the inferior frontal region which has developed abnormally during childhood in PWS.