Respiratory muscle incoordination in stuttering speech

How Stuttering Develops: The Multifactorial Dynamic Pathways Theory

Purpose

We advanced a multifactorial, dynamic account of the complex, nonlinear interactions of motor, linguistic, and emotional factors contributing to the development of stuttering. Our purpose here is to update our account as the multifactorial dynamic pathways theory.

Method

We review evidence related to how stuttering develops, including genetic/epigenetic factors; motor, linguistic, and emotional features; and advances in neuroimaging studies. We update evidence for our earlier claim: Although stuttering ultimately reflects impairment in speech sensorimotor processes, its course over the life span is strongly conditioned by linguistic and emotional factors.

Results

Our current account places primary emphasis on the dynamic developmental context in which stuttering emerges and follows its course during the preschool years. Rapid changes in many neurobehavioral systems are ongoing, and critical interactions among these systems likely play a major role in determining persistence of or recovery from stuttering.

Conclusion

Stuttering, or childhood onset fluency disorder (Diagnostic and Statistical Manual of Mental Disorders, 5th edition; American Psychiatric Association [APA], 2013), is a neurodevelopmental disorder that begins when neural networks supporting speech, language, and emotional functions are rapidly developing. The multifactorial dynamic pathways theory motivates experimental and clinical work to determine the specific factors that contribute to each child's pathway to the diagnosis of stuttering and those most likely to promote recovery.

Atypical non-verbal sensorimotor synchronization in adults who stutter may be modulated by auditory feedback

PURPOSE

To investigate if non-verbal sensorimotor synchronization abilities in adult individuals who stutter (IWS) differ from non-stuttering controls (NS) under various performance conditions (tempo, auditory feedback, use of hands [single/both] and rhythm).

METHODS

Participants were 11 IWS (5 males, 6 females, Mean age=25.8, SD=8.7) and 11 age- and gender-matched controls (Mean age=24.4, SD=8.4). During the experiment, participants were asked to prepare three melodies and subsequently perform them with a metronome at different rates and auditory feedback modalities (non-altered and suppressed). For each task/condition we tracked timing asynchrony related to the steady metronome beat.

RESULTS AND CONCLUSIONS

Overall, IWS displayed significantly higher timing asynchrony. Of all conditions, auditory-feedback distinguished IWS from NS most strongly, a subgroup of IWS significantly benefitting from the absence of auditory feedback. In addition, IWS showed a non-significant trend of higher negative mean asynchrony (NMA) and were more affected by the slower rate and increased rhythmic complexity and occasionally suggested poorer beat perception. These results suggest aberrant timing of sensorimotor network interaction associated with the origin of developmental stuttering.

Oral electromyography activation patterns for speech are similar in preschoolers who do and do not stutter

PURPOSE

In this study, the authors determined whether basic patterns of muscle activation for speech were similar in preschool children who stutter and in their fluent peers.

METHOD

Right and left lower lip muscle activity were recorded during conversational speech and sentence repetition in 64 preschool children diagnosed as stuttering (CWS) and in 40 children who do not stutter (CWNS). Measures of electromyography (EMG) amplitude, right-left asymmetry, and bilateral coordination were computed for fluent speech. The potential presence of tremor-like oscillations during disfluencies of CWS was assessed, and EMG amplitudes of fluent and disfluent speech were compared in CWS.

RESULTS

Across both speaking tasks, lip muscle activation was similar in CWS and CWNS in overall amplitude, bilateral synchrony, and degree of right-left asymmetry. EMG amplitude was reduced during disfluent compared with fluent conversational speech of CWS, and there was no evidence of tremor in the disfluencies of CWS.

CONCLUSION

These results support the assertion that stuttering in young children arises not from basic features of muscle contraction but rather from the command signals that control the timing and amplitude of muscle activity. The results indicate that no frank abnormality is present in muscle activation patterns in preschoolers who stutter.

Hypnotically assisted diaphragmatic exercises in the treatment of stuttering: a preliminary investigation

This preliminary study investigates the combined effect of intensive hypnotherapy and diaphragmatic exercises in the management of stuttering. Fifty-nine clients with stuttering were trained to practice abdominal weightlifting to strengthen their respiratory muscles and to improve their diaphragmatic movements. The weightlifting exercises involved lifting a dumbbell (2.0-4.0 kg) with the abdomen for 2 hours daily for 8 consecutive days. Hypnotherapy was utilized to alleviate anxiety, to boost self-confidence, and to increase motivation for weightlifting exercise. The pre- and postmeasures were statistically significant (p < .001). Results of the study provide support for the effectiveness of hypnotically assisted diaphragmatic training in the management of stuttering but should be further studied in controlled trials.

Functional lateralization of speech processing in adults and children who stutter

Developmental stuttering is a speech disorder in fluency characterized by repetitions, prolongations, and silent blocks, especially in the initial parts of utterances. Although their symptoms are motor related, people who stutter show abnormal patterns of cerebral hemispheric dominance in both anterior and posterior language areas. It is unknown whether the abnormal functional lateralization in the posterior language area starts during childhood or emerges as a consequence of many years of stuttering. In order to address this issue, we measured the lateralization of hemodynamic responses in the auditory cortex during auditory speech processing in adults and children who stutter, including preschoolers, with near-infrared spectroscopy. We used the analysis–resynthesis technique to prepare two types of stimuli: (i) a phonemic contrast embedded in Japanese spoken words (/itta/ vs. /itte/) and (ii) a prosodic contrast (/itta/ vs. /itta?/). In the baseline blocks, only /itta/ tokens were presented. In phonemic contrast blocks, /itta/ and /itte/ tokens were presented pseudo-randomly, and /itta/ and /itta?/ tokens in prosodic contrast blocks. In adults and children who do not stutter, there was a clear left-hemispheric advantage for the phonemic contrast compared to the prosodic contrast. Adults and children who stutter, however, showed no significant difference between the two stimulus conditions. A subject-by-subject analysis revealed that not a single subject who stutters showed a left advantage in the phonemic contrast over the prosodic contrast condition. These results indicate that the functional lateralization for auditory speech processing is in disarray among those who stutter, even at preschool age. These results shed light on the neural pathophysiology of developmental stuttering.

Análise perceptivo-auditiva e acústica da voz de indivíduos gagos

OBJETIVO: análise de desvios vocais em sujeitos com gagueira do desenvolvimento. MÉTODOS: participaram 23 sujeitos adultos, de ambos os sexos, com graus variados de gagueira, de acordo com a Escala de severidade de Yowa. Foi realizada análise perceptivo-auditiva da voz pela escala GIRBAS, com a inclusão de aspectos adicionais, além de análise acústica de parâmetros vocais e leitura espectrográfica. RESULTADOS: qualidade vocal alterada para 13% dos indivíduos, na vogal sustentada, com instabilidade (69,57% em grau leve e 20% em grau moderado) e rugosidade (48,70% em grau leve e 11,30% em grau moderado); alterações na normalidade na fala encadeada, com rugosidade (59,13% em grau leve e 1,74% em grau moderado) e tensão ocasional (46,08% em grau leve e 3,49% moderado). Foi encontrada grande inconsistência nos valores de tempo máximo de fonação intra-sujeito e elevada variabilidade inter-sujeitos. O padrão espectrográfico revelou instabilidade, tanto pela presença de quebra de sonoridade (21,74%), como pela presença de sub-harmônicos (30,43%), variabilidade da freqüência fundamental e qualidade vocal (8,7% para ambas). A análise dos parâmetros acústicos selecionados indicou alteração de shimmer (91,30%) e de jitter (34,78%). CONCLUSÕES: desvios vocais em gagos são discretos, mas evidenciados na tarefa de vogal sustentada, sem relação com o grau de gagueira. As alterações são sugestivas de instabilidade neuromotora no sistema fonoarticulatório.

Stuttering and natural speech processing of semantic and syntactic constraints on verbs

PURPOSE

Previous findings from event-related brain potentials (ERPs) indicate that adults who stutter (AWS) exhibit processing differences for visually presented linguistic information. This study explores how neural activations for AWS may differ for a linguistic task that does not require preparation for overt articulation or engage the articulatory loop for silent speech.

METHOD

Syntactic and semantic processing constraints were examined in AWS and adults who are normally fluent (AWNF) by assessment of their behavioral performance and ERPs in a natural speech listening task.

RESULTS

AWS performed similarly to AWNF in identifying verb-agreement violations and semantic anomalies, but ERPs elicited by syntactic and semantic constraints indicated atypical neural functions for AWS. ERPs of the AWNF displayed an expected N400 for reduced semantic expectations and a typical P600 for verb-agreement violations. In contrast, both N400s and P600s for the semantic and verb-agreement conditions were observed in the ERPs of the AWS.

CONCLUSIONS

The findings suggest that AWS may engage semantic-syntactic mechanisms more generally for semantic and syntactic processing. These findings converge with earlier studies using visual stimuli to indicate that whereas linguistic abilities are normal in AWS, underlying brain activity mediating some aspects of language processing may function differently.

Atypical neural functions underlying phonological processing and silent rehearsal in children who stutter

Phonological processing was examined in school-age children who stutter (CWS) by assessing their performance and recording event-related brain potentials (ERPs) in a visual rhyming task. CWS had lower accuracy on rhyming judgments, but the cognitive processes that mediate the comparisons of the phonological representations of words, as indexed by the rhyming effect (RE) ERP, were similar for the stuttering and normally fluent groups. Thus the lower behavioral accuracy of rhyming judgments by the CWS could not be attributed to that particular stage of processing. Instead, the neural functions for processes preceding the RE, indexed by the N400 and CNV elicited by the primes and the N400 elicited by the targets, suggest atypical processing that may have resulted in less efficient, less accurate rhyming judgment for the CWS. Based on the present results, it seems likely that the neural processes related to phonological rehearsal and target word anticipation, as indexed by the CNV, are distinctive for CWS at this age. Further, it is likely that the relative contributions of the left and right hemispheres differ in CWS in the stage of processing when linguistic integration occurs, as indexed by the N400. Taken together, these results suggest that CWS may be less able to form and retain a stable neural representation of the prime onset and rime as they anticipate the target presentation, which may lead to lower rhyming judgment accuracy.

Phenomenology of abnormal movements in stuttering

BACKGROUND

Stuttering is often accompanied by involuntary movements, abnormal gestures or changes in facial expression.

OBJECTIVE

To describe the incidence and phenomenology of abnormal movements (AMs) in stuttering patients.

MATERIALS AND METHODS

Eighty-five consecutive patients with stuttering and 119 normal controls videotaped and subsequently reviewed, in which AMs were classified as voluntary or involuntary, and as concurrent or unrelated to speech. Movement phenomenology was correlated with disease severity.

RESULTS

Of 85 stuttering patients studied, 51.7% had AMs and 22 more than one AM. Sixty-six different AMs were identified, of which 83.3% occurred during speech, 72.7% were classified as involuntary, and 27.2% as voluntary. Of 38 involuntary movements concurrent to speech, 25 were originally perceived as voluntary, but had since become involuntary through repeated use during stuttering. All involuntary movements not concurrent to speech fulfilled criteria for tics.

CONCLUSION

AMs occurring during stuttering were not always involuntary; movements not concurrent with speech clearly fulfilled clinical criteria for tics and were similar in incidence to normal controls. Inverse correlation was found between conscious control of movement during speech and stuttering severity. Many involuntary movements occurring during speech were clearly referred by patients as initially voluntary early on in the development of their speech disorder (starters or unblockers), underlining the importance of repetitive use of complex motor sequences as a source for putative involuntary movement genesis.

Respiratory control in stuttering speakers: evidence from respiratory high-frequency oscillations

This study tested the hypothesis that, in stuttering speakers, relations between the neural control systems for speech and life support, or metabolic breathing, may differ from relations previously observed in normally fluent subjects. Bilaterally coherent high-frequency oscillations in inspiratory-related EMGs, measured as maximum coherence in the frequency band of 60-110 Hz (MC-HFO), were used as indicators of participation by the brainstem controller for metabolic breathing in 10 normally fluent and 10 stuttering speakers. In all controls and most stuttering subjects, MC-HFO for speech was higher than or comparable to MC-HFO for deep breathing. For 4 stuttering subjects, higher MC-HFO was observed for speech than for deep breathing. Comparison of deep breathing to a speechlike breathing task yielded similar results. No relationship between MC-HFO during speech and severity of disfluency was observed. We conclude that in some stuttering speakers, the relations between respiratory controllers are atypical, but that high participation by the HFO-producing circuitry in the brainstem during speech is not sufficient to disrupt fluency.

Inspiratory muscle activity during bird song

The apparently continuous flow of bird song is in reality punctuated by brief periods of silence during which there are short inspirations called minibreaths. To determine whether these minibreaths are accompanied, and thus perhaps caused, by activity in inspiratory muscles, electromyographic (EMG) activity was recorded in M. scalenus in zebra finches and in M. scalenus and Mm. levatores costarum in cowbirds, together with EMGs from the abdominal expiratory muscles, air sac pressure and tracheal airflow. EMG activity in Mm. scalenus and levatores costarum consistently preceded the onset of negative air sac pressure by approximately 11 ms during both quiet respiration and singing in both species. The electrical activity of these two muscles was very similar. Compared with during quiet respiration, the amplitude of inspiratory muscle EMG during singing was increased between five- and 12-fold and its duration was decreased from >200 ms to on average 41 ms during minibreaths, again for both species, but inspiratory muscle activity did not overlap with that of the expiratory muscles. Thus, there was no indication that the inspiratory muscles acted either to shorten the duration of expiration or to reduce the expiratory effort as might occur if both expiratory and inspiratory muscles were simultaneously active. Inspiratory and expiratory muscle activities were highly stereotyped during song to the extent that together, they defined the temporal pattern of the songs and song types of individual birds.

Putative projection of phrenic afferents to the limbic cortex in humans studied with cerebral-evoked potentials

Respiratory sensations may rely in part on cortical integration of respiratory afferent information. In an attempt to study such projections, we recorded evoked potentials at scalp and cervical sites in 10 normal volunteers undergoing transcutaneous phrenic stimulation (0.1-ms square pulses, intensity liminal for diaphragmatic activation, series of 600 shocks at 2 Hz). A negative cerebral component of peak latency (12.79 +/- 0.54 ms; N13) was constant, and a negative spinal component (7.09 +/- 1.04 ms; N7) could also be recorded, all results being reproducible over time. Monitoring of cardiac frequency, skin anesthesia, and stimulation adjacent to the phrenic nerve made the phrenic origin of N7 and N13 the foremost hypothesis. Increasing stimulation frequency and comparison with median nerve stimulation provided arguments for the neural nature of the signals and their cerebral origin. Recordings from intracerebral electrodes in a patient showed a polarity reversal of the evoked potentials at the level of the cingulate gyrus. In conclusion, phrenic stimulation could allow one to study projections of phrenic afferents to the central nervous system in humans. Their exact site and physiological meaning remain to be clarified.

Stuttering may be a type of action dystonia

We observed abnormal involuntary movements, involving principally the facial and neck muscles, in 23 patients with stuttering. These movements were similar to involuntary movements seen in distinct dystonic syndromes. There was a history of stuttering in the first degree relatives of six patients. The association of stuttering with degenerative neurologic disorders and focal brain lesions, cerebral blood flow changes in patients with developmental stuttering, its occurrence as a side effect of centrally acting drugs, induction and alleviation of stuttering by mechanical perturbation, or by electrical stimulation of the thalamus, a strong genetic predisposition with male preponderance, and the statistically significant occurrence of stuttering in the family history of patients with idiopathic torsion dystonia suggest an organic basis for developmental stuttering. These findings and the reported similarities between the involuntary movements associated with stuttering and dystonic involuntary movements support the hypothesis that stuttering is a form of segmental or focal action dystonia.

Volume detection during voluntary and passive breathing

The ability to detect small changes in tidal volume (VT) during either volitional or passive breathing was compared in seven normal subjects. Passive breathing was achieved with positive pressure applied at the mouth by a ventilator. Although baseline breathing pattern was similar for each subject during the two types of breathing, the ability of the subjects to detect changes in VT was at least as good, and in general better, during passive as compared to volitional breathing. This suggests that the generation of a motor cortical command to inspire and the resultant respiratory muscle contraction are not essential to the perception of a change in lung volume. An increase in information from receptors in the mouth, pharynx and extrathoracic airways sensitive to positive pressure may be responsible for the increased ability of most subjects to detect changes in VT during passive breathing.