Vagus Nerve Stimulation as a Potential Adjuvant to Rehabilitation for Post-stroke Motor Speech Disorders

Optimizing non-invasive vagus nerve stimulation for treatment in stroke

Stroke remains a leading cause of long-term disability worldwide. There is an unmet need for neuromodulatory therapies that can mitigate against neurovascular injury and potentially promote neurological recovery. Transcutaneous vagus nerve stimulation has been demonstrated to show potential therapeutic effects in both acute and chronic stroke. However, previously published research has only investigated a narrow range of stimulation settings and indications. In this review, we detail the ongoing studies of transcutaneous vagus nerve stimulation in stroke through systematic searches of registered clinical trials. We summarize the upcoming clinical trials of transcutaneous vagus nerve stimulation in stroke, highlighting their indications, parameter settings, scope, and limitations. We further explore the challenges and barriers associated with the implementation of transcutaneous vagus nerve stimulation in acute stroke and stroke rehabilitation, focusing on critical aspects such as stimulation settings, target groups, biomarkers, and integration with rehabilitation interventions.

Two decades of vagus nerve stimulation for stroke: a bibliometric analysis

Background

Stroke is a major global health concern, imposing significant medical and social burdens. Vagus nerve stimulation (VNS), an emerging neuromodulation technology, has shown potential in the treatment of stroke. This bibliometric analysis aims to explore the knowledge structure and research trends in the field of VNS for stroke from 2004 to 2024.

Methods

Publications were retrieved from the Web of Science Core Collection. CiteSpace and VOSviewer were used to conduct bibliometric analyses, including author productivity, institutional contributions, and emerging research themes etc.

Results

A total of 191 eligible publications were analysed. Kilgard, M. P., and Hays, S. A. were the most prolific authors, each contributing 26 publications. The USA (96 publications), China (69 publications), and Scotland (17 publications) were the most prolific countries. The University of Texas at Dallas (33 publications) was the most prolific institution, followed by Chongqing Medical University (19 publications) and the University of Glasgow (15 publications). Future research is expected to focus on: (1) neurophysiological mechanisms of VNS in stroke recovery; (2) synergistic effects of VNS with other rehabilitation therapies; (3) comparative efficacy of non-invasive transauricular VNS versus invasive VNS; (4) safety and effectiveness of VNS for post-stroke functional impairments beyond motor rehabilitation; and (5) optimisation of VNS parameters for stroke treatment.

Conclusion

The field of VNS for stroke has experienced steady growth over the past two decades. This bibliometric analysis provides valuable insights to guide future research, clinical applications, and policy developments.

Vagus Nerve Stimulation in Stroke Management: Brief Review of Evolution and Present Applications Paired with Rehabilitation

Cerebrovascular accident (CVA) or stroke is a devastating neurological condition with dismal prognosis associated with recurrent episodes that further damage the neuronal networks, thus disabling neuronal plasticity. Vagus nerve stimulation (VNS) has been used in clinical practice to treat epilepsy for several decades and is well accepted as a safe procedure devoid of serious adverse events. Bailey and Bremer demonstrated that VNS has the capabilities to stimulate neuronal pathways that enhance the recovery of damaged cerebral function. Further studies have strengthened these observations, while technology has improved the tolerability of implants, resulting in VNS applications for epilepsy. Several animal models on neural plasticity have improved our understanding of VNS and its ability to provide neuromodulation to improve recovery in stroke patients. The closed-loop stimulation of the vagus nerve with individualized stimulation parameters combined with physical therapy appears to be an attractive option today. VNS is also being tested as a noninvasive trans-cutaneous modality to further improve patient acceptance and tolerability. However, the implantation of VNS is yielding desirable outcomes and appears to be a more reliable treatment for stroke rehabilitation in clinical trials.

Vagus nerve stimulation for stroke rehabilitation: Neural substrates, neuromodulatory effects and therapeutic implications

Paired vagus nerve stimulation (VNS) has emerged as a promising strategy to potentiate recovery after neurological injury. This approach, which combines short bursts of electrical stimulation of the vagus nerve with rehabilitation exercises, received approval from the US Food and Drug Aministration in 2021 as the first neuromodulation-based therapy for chronic stroke. Because this treatment is increasingly implemented in clinical practice, there is a need to take stock of what we know about this approach and what we have yet to learn. Here, we provide a survey on the foundational basis of VNS therapy for stroke and offer insight into the mechanisms that underlie potentiated recovery, focusing on the principles of neuromodulatory reinforcement. We discuss the current state of observations regarding synaptic reorganization in motor networks that are enhanced by VNS, and we propose other prospective loci of neuromodulation that should be evaluated in the future. Finally, we highlight the future opportunities and challenges to be faced as this approach is increasingly translated to clinical use. Collectively, a clearer understanding of the mechanistic basis of VNS therapy may reveal ways to maximize its benefits.

Research hotspots and frontiers of vagus nerve stimulation in stroke: a bibliometric analysis

Background

Vagus nerve stimulation (VNS) has emerged as a promising therapeutic approach for stroke treatment, drawing significant attention due to its potential benefits. However, despite this growing interest, a systematic bibliometric analysis of the research landscape is yet to be conducted.

Methods

We performed a comprehensive search of the Web of Science Core Collection (WoSCC) database for literature published between January 1, 2005, and August 31, 2024. CiteSpace and the Bibliometrix package in R software were used to generate knowledge maps and conduct a bibliometric analysis. This analysis focused on publication output, geographic distribution, institutional involvement, author and co-cited author networks, journal and co-cited journal relationships, co-cited references, and keyword trends.

Results

During the study period, 316 publications on VNS in stroke were identified, authored by 1,631 researchers from 1,124 institutions across 172 countries or regions. The number of publications showed steady growth, with the United States of America (USA) leading as the primary contributor. The University of Texas System emerged as the most active research institution. Frontiers in Neuroscience published the highest number of articles, while Stroke had the most citations. Professor Michael P. Kilgard authored the largest number of papers and was also the most frequently cited researcher. The main research trends focus on investigating VNS mechanisms via animal models and exploring its application in improving post-stroke sensorimotor function in the upper limbs. Moreover, VNS is showing promise in enhancing non-motor functions, such as swallowing, speech, and cognition, while addressing complications like post-stroke insomnia, depression, and disruptions in gut microbiota.

Conclusion

This bibliometric study offers a comprehensive overview of the research landscape and emerging trends in VNS for stroke rehabilitation, providing a solid foundation and reference point for future research directions in this field.

Non-Invasive Vagal Nerve Stimulation Pre-Treatment Reduces Neurological Dysfunction After Closed Head Injury in Mice

Non-invasive vagus nerve stimulation (nVNS) has recently been suggested as a potential therapy for traumatic brain injury (TBI). We previously demonstrated that nVNS inhibits cortical spreading depolarization, the electrophysiological event underlying migraine aura, and is relevant to TBI. Our past work also suggests a role for interleukin-1 beta (IL-1β) in cognitive deficits after closed head injury (CHI) in mice. We show that nVNS pre-treatment suppresses CHI-associated spatial learning and memory impairment and prevents IL-1β activation in injured neurons, but not endothelial cells. In contrast, nVNS administered 10 min after CHI was ineffective. These data suggest that nVNS prophylaxis might ameliorate neuronal dysfunction associated with CHI in populations at high risk for concussive TBI.

Bioelectronic Medicine: a multidisciplinary roadmap from biophysics to precision therapies

Bioelectronic Medicine stands as an emerging field that rapidly evolves and offers distinctive clinical benefits, alongside unique challenges. It consists of the modulation of the nervous system by precise delivery of electrical current for the treatment of clinical conditions, such as post-stroke movement recovery or drug-resistant disorders. The unquestionable clinical impact of Bioelectronic Medicine is underscored by the successful translation to humans in the last decades, and the long list of preclinical studies. Given the emergency of accelerating the progress in new neuromodulation treatments (i.e., drug-resistant hypertension, autoimmune and degenerative diseases), collaboration between multiple fields is imperative. This work intends to foster multidisciplinary work and bring together different fields to provide the fundamental basis underlying Bioelectronic Medicine. In this review we will go from the biophysics of the cell membrane, which we consider the inner core of neuromodulation, to patient care. We will discuss the recently discovered mechanism of neurotransmission switching and how it will impact neuromodulation design, and we will provide an update on neuronal and glial basis in health and disease. The advances in biomedical technology have facilitated the collection of large amounts of data, thereby introducing new challenges in data analysis. We will discuss the current approaches and challenges in high throughput data analysis, encompassing big data, networks, artificial intelligence, and internet of things. Emphasis will be placed on understanding the electrochemical properties of neural interfaces, along with the integration of biocompatible and reliable materials and compliance with biomedical regulations for translational applications. Preclinical validation is foundational to the translational process, and we will discuss the critical aspects of such animal studies. Finally, we will focus on the patient point-of-care and challenges in neuromodulation as the ultimate goal of bioelectronic medicine. This review is a call to scientists from different fields to work together with a common endeavor: accelerate the decoding and modulation of the nervous system in a new era of therapeutic possibilities.

Percutaneous Electrical Nerve Field Stimulation in Children and Adolescents With Functional Dyspepsia-Integrating a Behavioral Intervention

OBJECTIVES

Functional dyspepsia (FD) includes postprandial distress and epigastric pain syndrome. Percutaneous electrical nerve field stimulation (PENFS) in addition to behavioral interventions (BI) has shown benefits in children with functional abdominal pain but not specifically in FD. We aimed to assess the efficacy of PENFS for treating FD and compare the outcomes with those who received the combination of PENFS + BI.

MATERIALS AND METHODS

Charts of patients with FD who completed four weeks of PENFS were evaluated. A subset of patients received concurrent BI. Demographic data, medical history, and symptoms were documented. Outcomes at different time points included subjective symptom responses and validated questionnaires collected clinically (Abdominal Pain Index [API], Nausea Severity Scale [NSS], Functional Disability Inventory [FDI], Pittsburgh Sleep Quality Index [PSQI], Children's Somatic Symptoms Inventory [CSSI], Patient-Reported Outcomes Measurement Information Systems [PROMIS] Pediatric Anxiety and Depression scales).

RESULT

Of 84 patients, 61% received PENFS + BI, and 39% received PENFS alone. In the entire cohort, API (p < 0.0001), NSS (p = 0.001), FDI (p = 0.001), CSSI (p < 0.0001), PSQI (p = 0.01), PROMIS anxiety (p = 0.02), and depression (p = 0.01) scores improved from baseline to three weeks and at three months. Subjective responses showed nausea improvement (p = 0.01) and a trend for improvement in abdominal pain (p = 0.07) at week three. Abdominal pain subjectively improved at week three and three months (p = 0.003 and 0.02, respectively), nausea at week three and three months (p = 0.01 and 0.04, respectively), and a trend for improvement in sleep disturbances at week three and three months (p = 0.08 and p = 0.07, respectively) in the PENFS + BI group vs PENFS alone.

CONCLUSION

Abdominal pain, nausea, functioning, somatization, sleep disturbances, anxiety, and depression improved at three weeks and three months after PENFS in pediatric FD. Subjective pain and nausea improvement were greater in the PENFS + BI group than in the group with PENFS alone, suggesting an additive effect of psychologic therapy.

Transcutaneous auricular vagus nerve stimulation on upper limb motor function with stroke: a functional near-infrared spectroscopy pilot study

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (taVNS) emerges as a promising neuromodulatory technique. However, taVNS uses left ear stimulation in stroke survivors with either left or right hemiparesis. Understanding its influence on the cortical responses is pivotal for optimizing post-stroke rehabilitation protocols.

OBJECTIVE

The primary objective of this study was to elucidate the influence of taVNS on cortical responses in stroke patients presenting with either left or right hemiparesis and to discern its potential ramifications for upper limb rehabilitative processes.

METHODS

We employed functional near-infrared spectroscopy (fNIRS) to ascertain patterns of cerebral activation in stroke patients as they engaged in a "block transfer" task. Additionally, the Lateralization Index (LI) was utilized to quantify the lateralization dynamics of cerebral functions.

RESULTS

In patients exhibiting left-side hemiplegia, there was a notable increase in activation within the pre-motor and supplementary motor cortex (PMC-SMC) of the unaffected hemisphere as well as in the left Broca area. Conversely, those with right-side hemiplegia displayed heightened activation in the affected primary somatosensory cortex (PSC) region following treatment.Significantly, taVNS markedly amplified cerebral activation, with a pronounced impact on the left motor cortical network across both cohorts. Intriguingly, the LI showcased consistency, suggesting a harmonized enhancement across both compromised and uncompromised cerebral regions.

CONCLUSION

TaVNS can significantly bolster the activation within compromised cerebral territories, particularly within the left motor cortical domain, without destabilizing cerebral lateralization. TaVNS could play a pivotal role in enhancing upper limb functional restoration post-stroke through precise neuromodulatory and neuroplastic interventions.

How to fail with paired VNS therapy

Vagus nerve stimulation (VNS) has gained enormous traction as a promising bioelectronic therapy. In particular, the delivery of VNS paired with training to promote neural changes has demonstrated clinical success for stroke recovery and found far-reaching application in other domains, from autism to psychiatric disorders to normal learning. The success of paired VNS has been extensively documented. Here, we consider a more unusual question: why does VNS have such broad utility, and perhaps more importantly, when does VNS not work? We present a discussion of the concepts that underlie VNS therapy and an anthology of studies that describe conditions in which these concepts are violated and VNS fails. We focus specifically on the mechanisms engaged by implanted VNS, and how the parameters of stimulation, stimulation method, pharmacological manipulations, accompanying comorbidities, and specifics of concurrent training interact with these mechanisms to impact the efficacy of VNS therapy. As paired VNS therapy is increasing translated to clinical implementation, a clear understanding of the conditions in which it does, and critically, does not work is fundamental to the success of this approach.

Neuroimmunomodulation of vagus nerve stimulation and the therapeutic implications

Vagus nerve stimulation (VNS) is a technology that provides electrical stimulation to the cervical vagus nerve and can be applied in the treatment of a wide variety of neuropsychiatric and systemic diseases. VNS exerts its effect by stimulating vagal afferent and efferent fibers, which project upward to the brainstem nuclei and the relayed circuits and downward to the internal organs to influence the autonomic, neuroendocrine, and neuroimmunology systems. The neuroimmunomodulation effect of VNS is mediated through the cholinergic anti-inflammatory pathway that regulates immune cells and decreases pro-inflammatory cytokines. Traditional and non-invasive VNS have Food and Drug Administration (FDA)-approved indications for patients with drug-refractory epilepsy, treatment-refractory major depressive disorders, and headaches. The number of clinical trials and translational studies that explore the therapeutic potentials and mechanisms of VNS is increasing. In this review, we first introduced the anatomical and physiological bases of the vagus nerve and the immunomodulating functions of VNS. We covered studies that investigated the mechanisms of VNS and its therapeutic implications for a spectrum of brain disorders and systemic diseases in the context of neuroimmunomodulation.

Transcutaneous vagus nerve stimulation at nonspecific timings during training can compromise motor adaptation in healthy humans

Adding afferent vagus nerve stimulation to motor training via implanted electrodes can modify neuromotor adaptation depending on the stimulation timing. This study aimed to understand neuromotor adaptations when transcutaneous vagus nerve stimulation (tVNS) is applied at nonspecific timings during motor skill training in healthy humans. Twenty-four healthy young adults performed visuomotor training to match a complex force trajectory pattern with the index and little finger abduction forces concurrently. Participants were assigned to the tVNS group receiving tVNS at the tragus or the sham group receiving sham stimulation to the earlobe. The corresponding stimulations were applied at nonspecific timings throughout the training trials. Visuomotor tests were performed without tVNS or sham stimulation before and after training sessions across days. The reduction in the root mean square error (RMSE) against the trained force trajectory was attenuated in the tVNS group compared with the sham group, while its in-session reduction was not different between groups. The reduction of RMSE against an untrained trajectory pattern was not different between groups. No training effect was observed in corticospinal excitability or GABA-mediated intracortical inhibition. These findings suggest that adding tVNS at nonspecific timings during motor skill training can compromise motor adaptation but not transfer in healthy humans.NEW & NOTEWORTHY Adding vagus nerve stimulation via implanted electrodes during motor training can facilitate motor recovery in disabled animals and humans. No study examined the effect of transcutaneous vagus nerve stimulation (tVNS) during training on neuromotor adaptation in healthy humans. We have found that adding tVNS at nonspecific timings during motor skill training can compromise motor adaptation but not transfer in healthy humans.

Bibliometric analysis of publication trends and research hotspots in vagus nerve stimulation: A 20-year panorama

BACKGROUND

As a promising neuromodulation technique, vagus nerve stimulation (VNS) has been utilized to treat diverse diseases and the number of VNS studies has grown prosperously. Nonetheless, publication trends and research hotspots in this field remain unknown. This study aimed to perform a bibliometric analysis to systematically identify publication trends and research hotspots in VNS research within a 20-year panorama.

METHODS

The Web of Science Core Collection (WoSCC) database was retrieved to screen eligible VNS-related publications from 2002 to 2021. The online analytic tool of the WoSCC database was used to analyze various bibliometric parameters, such as the number of annual publications, the output of countries/regions, journals, total citations, citations per publication, and the Hirsch index. Bibliometrics (http://bibliometric.com/) and CiteSpace (version 5.6.R3) were used to identify research trends and hotspots.

RESULTS

A total of 7,283 publications were included for analysis. The annual number of publications increased stably but it increased significantly in recent years. The top five prolific countries were the United States, China, Germany, England, and France. The top five productive institutions were the University of California (Los Angeles), Harvard Medical School, Harvard University, University College London, and the University of Texas at Dallas. Notably, there was a geographical imbalance in countries and institutions. In addition, Epilepsy & Behavior, Epilepsia, and Plos One were the top three journals with the largest number of VNS publications. Michael P Kilgard was the most prolific author. Moreover, evolving research hotspots mainly included the effectiveness and mechanism of VNS on epilepsy, the role of VNS as an anti-inflammatory regulator, the application of VNS for psychiatric disorders, and the neuromodulation effect of VNS in headache management.

CONCLUSION

This study has revealed the overall publication trends and evolving research trends at a global level over a 20-year panorama. The potential collaborators, institutions, hotspots, and future research trends are also identified in this field, which will help guide new research directions of VNS.

Narrative Review of Noninvasive Brain Stimulation in Stroke Rehabilitation

Stroke is a disease with a high incidence and disability rate, resulting in changes in neural network and corticoid-subcortical excitability and various functional disabilities. The aim of the present study was to discuss the current status of research and limitations and potential direction in the application of noninvasive brain stimulation (NIBS) on post-stroke patients. This literature review focused on clinical studies and reviews. Literature retrieval was conducted in PubMed, Cochrane, Scopus, and CNKI, using the following keywords: Repeated transcranial magnetic stimulation, Transcranial direct current stimulation, Transcranial alternating current stimulation, Transcranial alternating current stimulation, Transcranial focused ultrasound, Noninvasive vagus nerve stimulation, Stroke, and Rehabilitation. We selected 200 relevant publications from 1985 to 2022. An overview of recent research on the use of NIBS on post-stroke patients, including its mechanism, therapeutic parameters, effects, and safety, is presented. It was found that NIBS has positive therapeutic effects on dysfunctions of motor, sensory, cognitive, speech, swallowing, and depression after stroke, but standardized stimulus programs are still lacking. The literature suggests that rTMS and tDCS are more beneficial to post-stroke patients, while tFUS and tVNS are currently less studied for post-stroke rehabilitation, but are also potential interventions.

Risk factors of dysphagia in patients with ischemic stroke: A meta-analysis and systematic review

Background

Dysphagia is a common yet serious complication in stroke patients. We aimed to conduct a meta-analysis and systematic review to evaluate the risk factors of dysphagia in patients with ischemic stroke, to provide insights to the clinical treatment and nursing care of dysphagia.

Methods

We searched PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure (CNKI) and Wanfang Database, China Biomedical Literature Database (CBM) for studies on dysphagia in patients with ischemic stroke up to January 31, 2022. The quality of the literature was evaluated using the Newcastle-Ottawa scale. Meta-analysis was performed using RevMan 5.3 software.

Results

A total of 10 studies involving 4637 ischemic stroke patients were included, 1183(25.51%) patients had dysphagia after stroke. The synthesized outcomes showed that elder age (SMD = 0.42, 95%CI:0.34–0.50), hypertension (OR = 1.96, 95%CI:1.48–2.61), diabetes (OR = 1.83, 95%CI:1.47–2.28), brainstem stroke (OR = 2.12, 95%CI:1.45–3.09) were associated with dysphagia in patients with ischemic stroke (all P<0.05). There was no significant difference in the gender between dysphagia and no dysphagia patients (OR = 1.07, 95%CI:0.91–1.27, P = 0.40). Egger regression tests indicated there were no significant publication biases in the synthesized outcomes (all P>0.05).

Conclusions

Elder age, hypertension, diabetes and brainstem stroke are associated with the development of dysphagia in patients with ischemic stroke. Attention should be paid to the assessment and early intervention of those risk factors for dysphagia to improve the prognosis of stroke patients.

Non-invasive Vagus Nerve Stimulation in Cerebral Stroke: Current Status and Future Perspectives

Stroke poses a serious threat to human health and burdens both society and the healthcare system. Standard rehabilitative therapies may not be effective in improving functions after stroke, so alternative strategies are needed. The FDA has approved vagus nerve stimulation (VNS) for the treatment of epilepsy, migraines, and depression. Recent studies have demonstrated that VNS can facilitate the benefits of rehabilitation interventions. VNS coupled with upper limb rehabilitation enhances the recovery of upper limb function in patients with chronic stroke. However, its invasive nature limits its clinical application. Researchers have developed a non-invasive method to stimulate the vagus nerve (non-invasive vagus nerve stimulation, nVNS). It has been suggested that nVNS coupled with rehabilitation could be a promising alternative for improving muscle function in chronic stroke patients. In this article, we review the current researches in preclinical and clinical studies as well as the potential applications of nVNS in stroke. We summarize the parameters, advantages, potential mechanisms, and adverse effects of current nVNS applications, as well as the future challenges and directions for nVNS in cerebral stroke treatment. These studies indicate that nVNS has promising efficacy in reducing stroke volume and attenuating neurological deficits in ischemic stroke models. While more basic and clinical research is required to fully understand its mechanisms of efficacy, especially Phase III trials with a large number of patients, these data suggest that nVNS can be applied easily not only as a possible secondary prophylactic treatment in chronic cerebral stroke, but also as a promising adjunctive treatment in acute cerebral stroke in the near future.