Luc F. De Nil

Functional neuroimaging of cerebellar activation during single word reading and verb generation in stuttering and nonstuttering adults

Articulatory discoordinations typically observed in fluent and disfluent speech of stuttering adults suggest an underlying deficiency in the precise timing needed for speech production. Positron emission tomography scans of stuttering adults showed generally higher cerebellar activations pre-treatment compared to nonstuttering control subjects. Intensive fluency treatment resulted in increased cerebellar activation during reading immediately post-treatment and a decrease to near normal levels at the 1 year follow scan. In contrast, verb generation resulted in a gradual but consistent decrease over the three scans. The results suggest that automaticity in motor and cognitive processes during speech production may need to be considered as an important factor in future investigations of stuttering.

Voxel-based morphometry of auditory and speech-related cortex in stutterers

Stutterers demonstrate unique functional neural activation patterns during speech production, including reduced auditory activation, relative to nonstutterers. The extent to which these functional differences are accompanied by abnormal morphology of the brain in stutterers is unclear. This study examined the neuroanatomical differences in speech-related cortex between stutterers and nonstutterers using voxel-based morphometry. Results revealed significant differences in localized grey matter and white matter densities of left and right hemisphere regions involved in auditory processing and speech production.

The effects of simulated stuttering and prolonged speech on the neural activation patterns of stuttering and nonstuttering adults.

Functional magnetic resonance imaging was used to investigate the neural correlates of passive listening, habitual speech and two modified speech patterns (simulated stuttering and prolonged speech) in stuttering and nonstuttering adults. Within-group comparisons revealed increased right hemisphere biased activation of speech-related regions during the simulated stuttered and prolonged speech tasks, relative to the habitual speech task, in the stuttering group. No significant activation differences were observed within the nonstuttering participants during these speech conditions. Between-group comparisons revealed less left superior temporal gyrus activation in stutterers during habitual speech and increased right inferior frontal gyrus activation during simulated stuttering relative to nonstutterers. Stutterers were also found to have increased activation in the left middle and superior temporal gyri and right insula, primary motor cortex and supplementary motor cortex during the passive listening condition relative to nonstutterers. The results provide further evidence for the presence of functional deficiencies underlying auditory processing, motor planning and execution in people who stutter, with these differences being affected by speech manner.

Speech-induced suppression of evoked auditory fields in children who stutter.

Auditory responses to speech sounds that are self-initiated are suppressed compared to responses to the same speech sounds during passive listening. This phenomenon is referred to as speech-induced suppression, a potentially important feedback-mediated speech-motor control process. In an earlier study, we found that both adults who do and do not stutter demonstrated a reduced amplitude of the auditory M50 and M100 responses to speech during active production relative to passive listening. It is unknown if auditory responses to self-initiated speech-motor acts are suppressed in children or if the phenomenon differs between children who do and do not stutter. As stuttering is a developmental speech disorder, examining speech-induced suppression in children may identify possible neural differences underlying stuttering close to its time of onset. We used magnetoencephalography to determine the presence of speech-induced suppression in children and to characterize the properties of speech-induced suppression in children who stutter. We examined the auditory M50 as this was the earliest robust response reproducible across our child participants and the most likely to reflect a motor-to-auditory relation. Both children who do and do not stutter demonstrated speech-induced suppression of the auditory M50. However, children who stutter had a delayed auditory M50 peak latency to vowel sounds compared to children who do not stutter indicating a possible deficiency in their ability to efficiently integrate auditory speech information for the purpose of establishing neural representations of speech sounds.

Auditory evoked fields to vocalization during passive listening and active generation in adults who stutter.

We used magnetoencephalography to investigate auditory evoked responses to speech vocalizations and non-speech tones in adults who do and do not stutter. Neuromagnetic field patterns were recorded as participants listened to a 1 kHz tone, playback of their own productions of the vowel /i/ and vowel-initial words, and actively generated the vowel /i/ and vowel-initial words. Activation of the auditory cortex at approximately 50 and 100 ms was observed during all tasks. A reduction in the peak amplitudes of the M50 and M100 components was observed during the active generation versus passive listening tasks dependent on the stimuli. Adults who stutter did not differ in the amount of speech-induced auditory suppression relative to fluent speakers. Adults who stutter had shorter M100 latencies for the actively generated speaking tasks in the right hemisphere relative to the left hemisphere but the fluent speakers showed similar latencies across hemispheres. During passive listening tasks, adults who stutter had longer M50 and M100 latencies than fluent speakers. The results suggest that there are timing, rather than amplitude, differences in auditory processing during speech in adults who stutter and are discussed in relation to hypotheses of auditory-motor integration breakdown in stuttering.

Oral kinesthetic deficit in adults who stutter : A target-accuracy study

The current study was based on the hypothesis that chronic developmental stuttering in adults involves a deficiency in oral kinesthesia. The authors used a target-accuracy task to compare oral kinesthesia in adults who stutter (n = 17) and in normal speakers (n = 17During the task, participants were instructed to make accurate jaw-opening movements in visual and nonvisual feedback conditions. The authors further contrasted oral movement control in a normal response time condition with that in a reaction time condition. Overall, the adults who stutter consistently made significantly less accurate and more variable movements than the control participants in the nonvisual condition, but particularly in the reaction time condition. In general, the present findings suggest that chronic developmental stuttering involves an oral kinesthetic deficiency, although without direct measures of somatosensory function, one cannot exclude a motor deficit interpretation.

Speech skill learning of persons who stutter and fluent speakers under single and dual task conditions

Two studies compared the accuracy and efficiency of initiating oral reading of nonsense syllables by persons who stutter (PWS) and fluent speakers (PNS) over practise. Findings of Study One, comparing 12 PWS and 12 PNS, replicated previous findings of slow speech sequence initiation over practise by PWS relative to PNS. In Study Two, nine PWS and eight PNS practised reading syllable sequences under single, and then dual task conditions in which a colour recognition distracter task was introduced. The speech sequences of PWS were initiated significantly slower than those of PNS. Significant Group×Condition interactions for reaction time and accuracy were interpreted to suggest that PNS, but not PWS, demonstrated the ability to switch between an attention‐demanding movement strategy under dual task conditions and a relatively automatic (little attention required) movement strategy after practise under single task conditions.

A clinician survey of speech and non-speech characteristics of neurogenic stuttering

UNLABELLED This study presents survey data on 58 Dutch-speaking patients with neurogenic stuttering following various neurological injuries. Stroke was the most prevalent cause of stuttering in our patients, followed by traumatic brain injury, neurodegenerative diseases, and other causes. Speech and non-speech characteristics were analyzed separately for these four etiology groups. Results suggested possible group differences, including site of lesion and influence of speech conditions on stuttering. Other characteristics, such as within-word localization of disfluencies and presence of secondary behaviors were comparable across the etiology groups. The implications of our results for the diagnosis of neurogenic stuttering will be discussed. EDUCATIONAL OBJECTIVES After reading this article, the reader will be able to: (1) provide a concise overview of the main literature on neurogenic stuttering; (2) discuss the speech and non-speech characteristics of neurogenic stuttering; (3) provide an overview of current clinical practices for intervention with neurogenic stuttering patients and their perceived outcome.

The trajectory of gray matter development in Broca's area is abnormal in people who stutter

The acquisition and mastery of speech-motor control requires years of practice spanning the course of development. People who stutter often perform poorly on speech-motor tasks thereby calling into question their ability to establish the stable neural motor programs required for masterful speech-motor control. There is evidence to support the assertion that these neural motor programs are represented in the posterior part of Broca’s area, specifically the left pars opercularis. Consequently, various theories of stuttering causation posit that the disorder is related to a breakdown in the formation of the neural motor programs for speech early in development and that this breakdown is maintained throughout life. To date, no study has examined the potential neurodevelopmental signatures of the disorder across pediatric and adult populations. The current study aimed to fill this gap in our knowledge. We hypothesized that the developmental trajectory of cortical thickness in people who stutter would differ across the lifespan in the left pars opercularis relative to a group of control participants. We collected structural magnetic resonance images from 116 males (55 people who stutter) ranging in age from 6 to 48 years old. Differences in cortical thickness across ages and between patients and controls were investigated in 30 brain regions previously implicated in speech-motor control. An interaction between age and group was found for the left pars opercularis only. In people who stutter, the pars opercularis did not demonstrate the typical maturational pattern of gradual gray matter thinning with age across the lifespan that we observed in control participants. In contrast, the developmental trajectory of gray matter thickness in other regions of interest within the neural network for speech-motor control was similar for both groups. Our findings indicate that the developmental trajectory of gray matter in left pars opercularis is abnormal in people who stutter.

The relationship between stuttering severity and kinesthetic acuity for jaw movements in adults who stutter

Abstract Previous research using a minimal movement paradigm has suggested a deficiency in the processing of oral kinesthetic sensations in adults who stutter. In the present study, the relationship between oral kinesthesia and stuttering severity was investigated. Eight stuttering adults (four very mild and four moderate/severe), and four normally fluent speakers were instructed to make the smallest possible movements with the jaw, both with and without continuous visual feedback. The adults with very mild stuttering showed a significantly larger increase in jaw displacement from the visual to the nonvisual condition compared to the normally fluent control group. Significant group differences also were found for movement duration. When only proprioceptive information was available to judge articulatory movements, the adults with moderate/severe stuttering took significantly longer than either of the other two subject groups to complete movements of the jaw. While providing partial support for the hypothesis that adults who stutter have a reduced oral kinesthetic acuity, the present data confirm previous findings that the most robust differences between stuttering and nonstuttering adults are observed for the movements of the jaw. The significance of this observation for our understanding of the role of temporal discoordinations in stuttering is discussed.