A causal link between left supplementary motor area and auditory-motor control of vocal production: Evidence by continuous theta burst stimulation

Causal Contributions and Interhemispheric Interactions of the Left and Right Supramarginal Gyri in Vocal Feedback Control: Insights From Dual-Site Transcranial Magnetic Stimulation

The bilateral supramarginal gyri (SMGs) have been implicated in sensorimotor control of speech production, yet their precise roles and interhemispheric interactions are poorly understood. This event-related potential study employed dual-site continuous theta burst stimulation (c-TBS) over the bilateral SMGs simultaneously to investigate their functional dynamics in vocal motor control. Following unilateral and bilateral c-TBS over the SMG as well as sham stimulation, participants vocalized the vowel sounds while exposed to unexpected pitch perturbations in auditory feedback. Unilateral real c-TBS paired with contralateral sham stimulation led to reduced vocal compensation magnitudes and latencies and decreased P2 responses compared to bilateral sham stimulation, with no differences between left and right SMG stimulation. Source localization revealed that decreased P2 responses following left SMG stimulation localized to left-lateralized dorsolateral prefrontal cortex, supplementary motor area, SMG, middle temporal gyrus, and temporo-parietal junction, whereas such decreases following right SMG stimulation involved left-lateralized primary motor cortex, premotor cortex, and middle temporal gyrus. These findings suggest that both SMGs are causally involved in vocal feedback control through distinct but interconnected networks. Surprisingly, dual-site c-TBS over the bilateral SMG did not alter vocal compensation or cortical activity, suggesting an interhemispheric balancing mechanism for fine-tuning vocal production. Our results offer novel insights into the bihemispheric coordination of auditory-vocal integration, highlighting potential treatment for speech disorders by modulating interhemispheric interactions.

Sensory Feedback in Parkinson Disease Voice Production: A Systematic Review

BACKGROUND

Understanding voice and speech impairments in Parkinson's disease (PD) is essential for developing effective interventions and ensuring efficient social communication.

OBJECTIVE

This review reports findings on voice perception and production in PD with a specific focus on sensory feedback (auditory and somatosensory) of the self-voice, neural correlates of the voice, and voice quality parameters such as pitch, loudness, and emotion modulation.

METHODS

A combined bibliometric analysis and a systematic review should identify key trends and knowledge gaps in the neuroimaging (functional magnetic resonance imaging (fMRI)/EEG) literature on PD self-voice processing.

RESULTS

EEG studies focusing on pitch revealed significant differences in the P200 event-related potential, but no differences in the N100, between healthy controls and individuals with PD. fMRI studies showed reduced activation in the motor cortex and basal ganglia during speech production in PD, accompanied by increased activation in other brain regions, such as the auditory cortex, which was associated with pitch variability and loudness control. A decrease in right dorsal premotor cortex activation was linked to impaired voice control, particularly regarding loudness modulation. Additionally, the review identified missing research on the emotion modulation of the voice, despite its critical role in social communication. Altered sensory feedback plays a significant role in compensatory cortical responses during vocalization, underscoring the importance of sensory feedback in maintaining normal voice production in PD.

CONCLUSIONS

This review identified missing research on voice loudness perception and the potential impact of emotion perception deficits regarding voice modulation in persons with PD.

Understanding the effects of different transcranial magnetic stimulation control protocols: a behavioral and neural perspective

Transcranial magnetic stimulation (TMS) is a noninvasive stimulation technique for modulating brain activity. However, selecting optimal control protocols to account for their neural and non-neural effects remains a challenge. To this end, the present event-related potential (ERP) study investigated the behavioral and neural effects of three commonly used control protocols, namely, sham stimulation and real stimulation with continuous theta burst stimulation (c-TBS) over the vertex and primary visual cortex (V1), on a given task manipulating pitch in voice auditory feedback. The results showed no significant differences in vocal and ERP responses to pitch perturbations among the three TMS control protocols, suggesting their comparable neural and non-neural influences on vocal feedback control. Compared with the baseline condition (no TMS), all three TMS control protocols led to intact vocal compensations but prolonged N1 latencies and reduced P2 amplitudes, potentially linked to nonspecific stimulation effects or placebo-like responses. These findings provide the first neurobehavioral evidence for comparable effects across different TMS control protocols on vocal pitch regulation, offering insights for selecting optimal control strategies to explore the causal mechanisms of auditory-vocal integration. They also emphasize the importance of including a baseline condition to disentangle genuine TMS effects.NEW & NOTEWORTHY This is the first study to provide neurobehavioral evidence comparing the effects of three transcranial magnetic stimulation (TMS) control protocols on vocal feedback control. The findings suggest that sham stimulation and real stimulation [continuous theta burst stimulation (c-TBS) over vertex and V1] produce similar neural and non-neural effects on vocal pitch regulation. Despite no differences in vocal responses, all protocols led to prolonged N1 latencies and reduced P2 amplitudes, emphasizing the importance of including a baseline condition to isolate genuine TMS effects.

HD-tDCS over left supplementary motor area differentially modulated neural correlates of motor planning for speech vs. limb movement

The supplementary motor area (SMA) is implicated in planning, execution, and control of speech production and limb movement. The SMA is among putative generators of pre-movement EEG activity which is thought to be neural markers of motor planning. In neurological conditions such as Parkinson's disease, abnormal pre-movement neural activity within the SMA has been reported during speech production and limb movement. Therefore, this region can be a potential target for non-invasive brain stimulation for both speech and limb movement. The present study took an initial step in examining the application of high-definition transcranial direct current stimulation (HD-tDCS) over the left SMA in 24 neurologically intact adults. Subsequently, event-related potentials (ERPs) were recorded while participants performed speech and limb movement tasks. Participants' data were collected in three counterbalanced sessions: anodal, cathodal and sham HD-tDCS. Relative to sham stimulation, anodal, but not cathodal, HD-tDCS significantly attenuated ERPs prior to the onset of the speech production. In contrast, neither anodal nor cathodal HD-tDCS significantly modulated ERPs prior to the onset of limb movement compared to sham stimulation. These findings showed that neural correlates of motor planning can be modulated using HD-tDCS over the left SMA in neurotypical adults, with translational implications for neurological conditions that impair speech production. The absence of a stimulation effect on ERPs prior to the onset of limb movement was not expected in this study, and future studies are warranted to further explore this effect.

Using altered auditory feedback to study pitch compensation and adaptation in tonal language speakers

Human speech production is strongly influenced by the auditory feedback it generates. Auditory feedback-what we hear when we speak-enables us to learn and maintain speaking skills and to rapidly correct errors in our speech. Over the last three decades, the real-time altered auditory feedback (AAF) paradigm has gained popularity as a tool to study auditory feedback control during speech production. This method involves changing a speaker's speech and feeding it back to them in near real time. More than 50% of the world's population speak tonal languages, in which the pitch or tone used to pronounce a word can change its meaning. This review article aims to offer an overview of the progression of AAF paradigm as a method to study pitch motor control among speakers of tonal languages. Eighteen studies were included in the current mini review and were compared based on their methodologies and results. Overall, findings from these studies provide evidence that tonal language speakers can compensate and adapt when receiving inconsistent and consistent pitch perturbations. Response magnitude and latency are influenced by a range of factors. Moreover, by combining AAF with brain stimulation and neuroimaging techniques, the neural basis of pitch motor control in tonal language speakers has been investigated. To sum up, AAF has been demonstrated to be an emerging tool for studying pitch motor control in speakers of tonal languages.

Neural alpha oscillations index context-driven perception of ambiguous vowel sequences

Perception of bistable stimuli is influenced by prior context. In some cases, the interpretation matches with how the preceding stimulus was perceived; in others, it tends to be the opposite of the previous stimulus percept. We measured high-density electroencephalography (EEG) while participants were presented with a sequence of vowels that varied in formant transition, promoting the perception of one or two auditory streams followed by an ambiguous bistable sequence. For the bistable sequence, participants were more likely to report hearing the opposite percept of the one heard immediately before. This auditory contrast effect coincided with changes in alpha power localized in the left angular gyrus and left sensorimotor and right sensorimotor/supramarginal areas. The latter correlated with participants' perception. These results suggest that the contrast effect for a bistable sequence of vowels may be related to neural adaptation in posterior auditory areas, which influences participants' perceptual construal level of ambiguous stimuli.

The overgeneralization of pain-related fear in individuals with higher pain sensitivity: A behavioral and event-related potential study

Fear generalization contributes to the development and maintenance of pain. Pain sensitivity has been proposed to predict the strength of fear responses to aversive stimuli. However, whether individual variation in pain sensitivity affects pain-related fear generalization and its underlying cognitive processing remains unclear. To address this gap, we recorded behavioral and event-related potential (ERP) data among 22 high pain sensitivity (HPS) and 22 low pain sensitivity (LPS) healthy adults when exposed to a fear generalization paradigm. The behavioral results indicate that the HPS group displayed higher unconditioned stimulus expectancy and greater fear, arousal, and anxiety ratings to conditioned stimulus and generalization stimulus than the LPS group (all p values < 0.05). The ERP results showed that the HPS group exhibited a larger late positive potential evoked by GS2, GS3 and CS- (all p < 0.005) but a smaller N1 evoked by all CS and GSs (all p values < 0.05) relative to the LPS group. These findings suggest that individuals with a high level of pain sensitivity allocate more attention resources to pain-related threatening stimuli, which contributes to an overgeneralization of pain-related fear.

Right, but not left, posterior superior temporal gyrus is causally involved in vocal feedback control

The posterior superior temporal gyrus (pSTG) has been implicated in the integration of auditory feedback and motor system for controlling vocal production. However, the question as to whether and how the pSTG is causally involved in vocal feedback control is currently unclear. To this end, the present study selectively stimulated the left or right pSTG with continuous theta burst stimulation (c-TBS) in healthy participants, then used event-related potentials to investigate neurobehavioral changes in response to altered auditory feedback during vocal pitch regulation. The results showed that, compared to control (vertex) stimulation, c-TBS over the right pSTG led to smaller vocal compensations for pitch perturbations accompanied by smaller cortical N1 and larger P2 responses. Enhanced P2 responses received contributions from the right-lateralized temporal and parietal regions as well as the insula, and were significantly correlated with suppressed vocal compensations. Surprisingly, these effects were not found when comparing c-TBS over the left pSTG with control stimulation. Our findings provide evidence, for the first time, that supports a causal relationship between right, but not left, pSTG and auditory-motor integration for vocal pitch regulation. This lends support to a right-lateralized contribution of the pSTG in not only the bottom-up detection of vocal feedback errors but also the involvement of driving motor commands for error correction in a top-down manner.

DIVA Meets EEG: Model Validation Using Formant-Shift Reflex

The neurocomputational model 'Directions into Velocities of Articulators' (DIVA) was developed to account for various aspects of normal and disordered speech production and acquisition. The neural substrates of DIVA were established through functional magnetic resonance imaging (fMRI), providing physiological validation of the model. This study introduces DIVA_EEG an extension of DIVA that utilizes electroencephalography (EEG) to leverage the high temporal resolution and broad availability of EEG over fMRI. For the development of DIVA_EEG, EEG-like signals were derived from original equations describing the activity of the different DIVA maps. Synthetic EEG associated with the utterance of syllables was generated when both unperturbed and perturbed auditory feedback (first formant perturbations) were simulated. The cortical activation maps derived from synthetic EEG closely resembled those of the original DIVA model. To validate DIVA_EEG, the EEG of individuals with typical voices (N = 30) was acquired during an altered auditory feedback paradigm. The resulting empirical brain activity maps significantly overlapped with those predicted by DIVA_EEG. In conjunction with other recent model extensions, DIVA_EEG lays the foundations for constructing a complete neurocomputational framework to tackle vocal and speech disorders, which can guide model-driven personalized interventions.

Transcranial direct current stimulation over left dorsolateral prefrontal cortex facilitates auditory-motor integration for vocal pitch regulation

Background

A growing body of literature has implicated the left dorsolateral prefrontal cortex (DLPFC) in the online monitoring of vocal production through auditory feedback. Specifically, disruption of or damage to the left DLPFC leads to exaggerated compensatory vocal responses to altered auditory feedback. It is conceivable that enhancing the cortical excitability of the left DLPFC may produce inhibitory influences on vocal feedback control by reducing vocal compensations.

Methods

We used anodal transcranial direct current stimulation (a-tDCS) to modulate cortical excitability of the left DLPFC and examined its effects on auditory-motor integration for vocal pitch regulation. Seventeen healthy young adults vocalized vowel sounds while hearing their voice pseudo-randomly pitch-shifted by ±50 or ±200 cents, either during (online) or after (offline) receiving active or sham a-tDCS over the left DLPFC.

Results

Active a-tDCS over the left DLPFC led to significantly smaller peak magnitudes and shorter peak times of vocal compensations for pitch perturbations than sham stimulation. In addition, this effect was consistent regardless of the timing of a-tDCS (online or offline stimulation) and the size and direction of the pitch perturbation.

Conclusion

These findings provide the first causal evidence that a-tDCS over the left DLPFC can facilitate auditory-motor integration for compensatory adjustment to errors in vocal output. Reduced and accelerated vocal compensations caused by a-tDCS over left DLPFC support the hypothesis of a top-down neural mechanism that exerts inhibitory control over vocal motor behavior through auditory feedback.