Biology subjects

Demirel, B.

Publications and source records attributed to Demirel, B..

3 recordsLinked to original sources

bioRxiv2026

Differences in dynamic motor selection in stuttering

Stuttering involves interruptions to the smooth flow of speech occurring mostly at syllable onset.1 Speech fluency is enhanced in people who stutter (PWS) by external timing cues.2 This has been taken to indicate that difficulties in the temporal organisation of action selection and initiation during speech contribute to stuttering.3 An important unanswered question is whether putative temporal coordination difficulties are specific to speech or generalise to other actions. Here, we examined the temporal organisation of hand action selection in PWS. Twenty PWS and twenty typically fluent speakers (TFS) underwent magnetoencephalography (MEG) recording while performing a visuomotor working-memory task that encouraged temporally specific selection, preparation, and shifts between hand actions. Lateralised sensorimotor mu/beta-frequency (8-30 Hz) activity modulation accompanying hand-action prioritisation was weaker in PWS than TFS. Strikingly, this effect was specific to a period of high uncertainty regarding which action to select and when. Despite these differences, lateralised mu/beta modulation was functionally related to reaction times in both groups and reaction times were well matched between PWS and TFS. The findings suggest a general disruption of temporal structuring of action selection and preparation in stuttering.

neuroscience↗

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↗