Biology subjects

Chesters, J.

Publications and source records attributed to Chesters, J..

5 recordsLinked to original sources

bioRxiv2025

Differences in brain activity during sentence repetition in people who stutter: a combined analysis of four fMRI studies

Our understanding of the neural correlates of developmental stuttering benefits from the use of functional MRI (fMRI) during speech production. Despite two decades of research, however, we have reached little consensus. In the current study, we analysed pooled fMRI data from four different studies that used the same sentence reading task and methodological approach. The combined sample included 56 adolescents and adults who stutter and 53 demographically matched typically fluent controls. A sparse-sampling design was used in each study, in which participants spoke during the silent period between measurements of brain activity. Sentence reading evoked activity in both groups across frontal and temporal regions bilaterally. At statistical thresholds corrected for family-wise error, there were no significant group differences. An uncorrected threshold was applied to explore group differences in areas previously identified in earlier fMRI studies on stuttering. People who stutter (PWS) showed greater activity compared with controls in right frontal pole, right anterior insula extending to frontal operculum, left planum temporale, and midbrain, at the level of red nucleus. In contrast, PWS showed lower activity in left superior frontal sulcus, subgenual medial prefrontal cortex, right anterior temporal lobe, and portions of inferior parietal lobe bilaterally including the angular gyrus on the left. Despite pooling data across multiple studies to achieve a relatively large sample, group differences in regions involved in speech-motor control only emerged at an uncorrected voxel-wise threshold. Some of these findings align with previous fMRI studies, such as increased activity in the right anterior insular cortex.

neuroscience↗

bioRxiv2024

No Evidence of Altered Language Laterality in People Who Stutter across Different Brain Imaging Studies of Speech and Language

A long-standing neurobiological explanation of stuttering is the incomplete cerebral dominance theory, which refers to competition between two hemispheres for "dominance" over handedness and speech, causing altered language lateralisation. Renewed interest in these ideas came from brain imaging findings in people who stutter (PWS) of increased activity in the right hemisphere during speech production or of shifts in activity from right to left when fluency increased. Here, we revisited this theory using functional MRI data from children and adults who stutter, and typically fluent speakers (119 participants in total) during four different speech and language tasks: overt sentence reading, overt picture description, covert sentence reading and covert auditory naming. Laterality indices (LIs) were calculated for the frontal and temporal lobes using the LI toolbox running in Statistical Parametric Mapping. We also repeated the analyses with more specific language regions, namely the pars opercularis (Brodmann Area 44) and pars triangularis (Brodmann Area 45). Laterality indices in PWS and typically fluent speakers (TFS) did not differ and Bayesian analyses provided moderate to anecdotal levels of support for the null hypothesis (i.e., no differences in laterality in PWS compared with TFS). The proportions of the PWS and TFS who were left lateralised or had atypical rightwards or bilateral lateralisation did not differ. We found no support for the theory that language laterality is reduced or differs in PWS compared with TFS.

neuroscience↗

bioRxiv2020

An fMRI study of initiation and inhibition of manual responses in people who stutter

Developmental stuttering is a speech motor disorder characterised by difficulties initiating speech and frequent interruptions to the speech flow. Previous work suggests that people who stutter (PWS) have an overactive response suppression mechanism. Imaging studies of speech production in PWS consistently reveal greater activity of the right inferior frontal cortex, an area robustly implicated in inhibitory control of both manual and spoken responses. Here, we used a manual response version of the stop-signal task during fMRI to investigate neural differences related to response initiation and inhibition in PWS. Behaviourally, PWS were slower to respond to go stimuli than people who are typically fluent (PWTF), but there was no difference in stop-signal reaction time. Our fMRI results were consistent with these behavioural results. The fMRI analysis revealed the expected networks associated with manual response initiation and inhibition in both groups. However, all contrasts between the two groups were characterised by overactivity in PWS relative to PWTF. This overactivity was significantly different for the initiation of responses (i.e. the go trials) but not for response inhibition (i.e. the stop trials). One explanation of these results is that PWS are consistently in a heightened inhibition state, i.e. areas of the inhibition network are more active, generally. This interpretation is consistent with predictions from the global response suppression hypothesis.

neuroscience↗

bioRxiv2018

Transcranial direct current stimulation over left inferior frontal cortex improves speech fluency in adults who stutter

Stuttering is a neurodevelopmental disorder affecting 5% of children, and persisting in 1% of adults. Promoting lasting fluency improvement in adults who stutter is a particular challenge. Novel interventions to improve outcomes are required, therefore. Previous work in patients with acquired motor and language disorders reported enhanced benefits of behavioural therapies when paired with transcranial direct current stimulation (tDCS). Here, we report the results of the first trial investigating whether tDCS can improve speech fluency in adults who stutter. Thirty adult men who stutter completed a randomized, double-blind, controlled trial of anodal tDCS over left inferior frontal cortex. Fifteen men received 20 minutes of 1-mA tDCS on five consecutive days while speech fluency was temporarily induced using choral and metronome-timed speech. The other 15 men received the same speech fluency intervention with sham stimulation. We predicted that applying anodal tDCS to the left inferior frontal cortex during speech production with temporary fluency inducers would result in longer-lasting fluency improvements. Speech fluency during reading and conversation was assessed at baseline, before and after the stimulation on each day of the five-day intervention, and at 1 and 6 weeks after the end of the intervention. TDCS combined with speech fluency training significantly reduced the percentage of disfluent speech measured 1 week after the intervention compared with fluency intervention alone. At 6 weeks after the intervention, this improvement was maintained during reading but not during conversation. Outcome scores at both post-intervention time points on a clinical assessment tool (the Stuttering Severity Instrument - version 4) also showed significant improvement in the group receiving tDCS compared with the sham group, in whom fluency was unchanged from baseline. We conclude that tDCS combined with behavioural fluency intervention has the capacity to improve fluency in adults who stutter. tDCS thereby offers a potentially useful adjunct to future speech therapy interventions for this population, for whom therapy outcomes are currently limited.

neuroscience↗

bioRxiv2017

Facilitation of motor excitability during listening to spoken sentences is not modulated by noise or semantic coherence

Comprehending speech can be particularly challenging in a noisy environment and in the absence of semantic context. It has been proposed that the articulatory motor system would be recruited especially in difficult listening conditions. However, it remains unknown how signal-to-noise ratio (SNR) and semantic context affect the recruitment of the articulatory motor system when listening to continuous speech. The aim of the present study was to address the hypothesis that involvement of the articulatory motor cortex increases when the intelligibility and clarity of the spoken sentences decreases, because of noise and the lack of semantic context. We applied Transcranial Magnetic Stimulation (TMS) to the lip and hand representations in the primary motor cortex and measured motor evoked potentials from the lip and hand muscles, respectively, to evaluate motor excitability when young adults listened to sentences. In Experiment 1, we found that the excitability of the lip motor cortex was facilitated during listening to both semantically anomalous and coherent sentences in noise, but neither SNR nor semantic context modulated the facilitation. In Experiment 2, we replicated these findings and found no difference in the excitability of the lip motor cortex between sentences in noise and clear sentences without noise. Thus, our results show that the articulatory motor cortex is involved in speech processing even in optimal and ecologically valid listening conditions and that its involvement is not modulated by the intelligibility and clarity of speech.

neuroscience↗