Research study: "Neural oscillatory activity and connectivity in children who stutter during a non-speech motor task" (2022) by Soo-Eun Chang et al

Research study: "Neural oscillatory activity and connectivity in children who stutter during a non-speech motor task" (2022) by Soo-Eun Chang et al Research: [https://www.biorxiv.org/content/10.1101/2022.10.19.512866v1.full](https://www.biorxiv.org/content/10.1101/2022.10.19.512866v1.full) PDF document: [https://www.biorxiv.org/content/10.1101/2022.10.19.512866v1.full.pdf](https://www.biorxiv.org/content/10.1101/2022.10.19.512866v1.full.pdf) ## Abstract Neural motor control rests on the dynamic interaction of cortical and subcortical regions, which is reflected in the modulation of oscillatory activity and connectivity in multiple frequency bands. Motor control is thought to be compromised in developmental stuttering, particularly involving circuits in the left hemisphere that support speech, movement initiation and timing control. However, to date evidence comes from adult studies, with limited understanding about motor processes in childhood, closer to the onset of stuttering. In this study, we investigated the neural control of movement initiation in children who stutter and children who do not stutter by evaluating transient changes of EEG oscillatory activity and connectivity during a simple button press motor task. We found reduced modulation of left hemisphere oscillatory power, phase locking to button press and phase connectivity in children who stutter compared to children who do not stutter, consistent with previous findings of dysfunction within the left sensorimotor circuits. Interhemispheric connectivity was also weaker at lower frequencies (delta, theta) and stronger in the beta band in children who stutter than in children who do not stutter. Taken together, these findings indicate weaker engagement of the contralateral left motor network in children who stutter even during low-demand non-speech tasks, and suggest that the right hemisphere might be recruited to support sensorimotor processing in childhood stuttering. Differences in oscillatory dynamics occurred despite comparable task performance between groups, indicating that altered balance of cortical activity might be a core aspect of stuttering, observable during normal motor behavior. ## Motor Control in Stuttering * **Deficits in Motor Control:** * Individuals who stutter show deficits in action initiation and timing, evident in both speech and non-speech motor tasks. * Even during perceptually fluent speech, stutterers exhibit more variable speech movements. * **Non-Speech Motor Performance:** * People who stutter perform worse in demanding non-speech motor tasks, though results are mixed for simpler tasks like hand claps. * These behavioral differences suggest subtle structural and functional anomalies in the sensorimotor system. * **Neural Differences:** * Structural and functional differences are observed in sensorimotor areas, with reduced size, activation, and connectivity in the left hemisphere, and increased size and activation in the right hemisphere, potentially as compensatory mechanisms. * The left hemisphere is suggested as the core disruption site in stuttering, with right hemisphere changes developing over time. ## Neural Oscillations in Motor Control * **Beta Oscillations:** * Beta oscillations (13-30 Hz) are crucial for sensorimotor processing and motor control. * These oscillations are suppressed during movement planning and execution and increase post-movement. * In stuttering, beta modulation during speech tasks is altered, though findings vary regarding increased or decreased modulation and the hemisphere involved. * **Slow Oscillations (Delta and Theta):** * Delta (2-4 Hz) and theta (5-7 Hz) oscillations are important for coordinating the motor network. * These oscillations synchronize across regions during movement, indicating functional integration of the motor network. ## Study Rationale and Hypotheses * **Previous Research:** * Limited studies on beta modulation in stuttering during speech tasks show heterogeneous results. * Slow oscillatory connectivity and its role in stuttering have not been extensively studied, particularly in non-speech tasks. * **Current Study Objectives:** * Investigate spatiotemporal patterns of sensorimotor activity (oscillatory power) and functional coupling (phase synchronization) during a non-speech motor task in children who stutter. * Examine neural oscillations elicited by a simple button-press task to ensure comparable performance across groups. * **Predictions:** * Differences in power modulation and phase synchronization in the left hemisphere (contralateral to the response hand). * No expected behavioral differences in average accuracy or response time due to task simplicity. * Greater variability in response time and neural variability (phase locking to button press) in children who stutter, indicating less consistent neural dynamics in the left hemisphere. Current research examined the spatiotemporal dynamics of sensorimotor oscillatory activity and connectivity during movement initiation in children who stutter compared to children who do not stutter. Both groups performed a button-press task in response to auditory targets. Behavioral performance was similar in speed and accuracy, but children who stutter exhibited different oscillatory dynamics and network connectivity, indicating differences in general sensorimotor control. ## Research findings: **Behavioral Performance:** * Comparable accuracy and mean response time between both groups. * Slightly higher variability in response timing in children who stutter, but not statistically significant. **Beta Power Modulation:** * Children who stutter showed a lack of left lateralized peri-motor beta power modulation. * After button press, beta power increased in the left hemisphere for children who do not stutter but decreased in children who stutter. * Weaker modulation of left peri-motor beta power in children who stutter mirrors findings in adults who stutter, indicating reduced activation of motor preparation networks. **Oscillatory Synchronization:** * Typically developing children displayed widespread increase in slow frequency (delta/theta) synchronization and left-lateralized beta synchronization during the task. * Children who stutter showed smaller increases in slow frequency synchronization, affecting both hemispheres and interhemispheric connections. * Increased interhemispheric beta synchronization in children who stutter, suggesting potential recruitment of the right hemisphere even in simple tasks. **Phase Synchronization:** * Children who do not stutter had stronger transient phase locking to button press in delta and theta bands, particularly over the left hemisphere. * Children who stutter showed less lateralized delta phase locking, indicating potential variability in motor timing. ## Interpretation and Implications: **Beta Rebound:** * Weaker beta rebound in children who stutter could indicate reduced inhibition or altered sensory feedback processing post-movement. This aligns with theories suggesting unstable internal models in stuttering. **Oscillatory Connectivity:** * Reduced delta/theta synchronization in children who stutter suggests less efficient motor network communication, potentially impacting complex motor planning. * Increased interhemispheric beta synchronization may indicate compensatory mechanisms involving the right hemisphere. **Phase Locking:** * Weaker left-lateralized phase locking in delta band for children who stutter suggests greater variability in motor activity timing, though not reflected in significant response time variability. ## Conclusions The onset of movement is reliably accompanied by changes in oscillatory activity in the motor cortex, particularly in the hemisphere contralateral to the moving hand. In this study, we identified several differences in oscillatory dynamics between children who stutter and children who do not stutter, indexed by reduced modulation of power and phase synchronization over the left hemisphere, reduced lateralization of phase locking to movement initiation at slow frequencies, and altered interhemispheric phase synchronization in the delta and beta bands. Taken together, these results point to deficits in left sensorimotor cortex function in stuttering that may not be limited to speech, and suggest that the right hemisphere may be recruited to support sensorimotor processing even in childhood developmental stuttering. The study reveals that children who stutter exhibit distinct patterns of sensorimotor oscillatory dynamics and connectivity during non-speech movements. These differences, especially in beta power modulation and phase synchronization, highlight potential underlying neural mechanisms contributing to stuttering. Future research should explore these findings in more complex motor tasks and investigate how these neural dynamics relate to speech motor control in stuttering.