A Review of Parameter Settings for Invasive and Non-invasive Vagus Nerve Stimulation (VNS) Applied in Neurological and Psychiatric Disorders

State- and frequency-dependence in autonomic rebalance mediated by intradermal auricular electroacupuncture stimulation

Background

Vagus nerve stimulation (VNS) improves diseases such as refractory epilepsy and treatment-resistant depression, likely by rebalancing the autonomic nervous system (ANS). Intradermal auricular electro-acupuncture stimulation (iaES) produces similar effects. The aim of this study was to determine the effects of different iaES frequencies on the parasympathetic and sympathetic divisions in different states of ANS imbalance.

Methods

We measured heart rate variability (HRV) and heart rate (HR) of non-modeled (normal) rats with the treatment of various frequencies to determine the optimal iaES frequency. The optimized iaES frequency was then applied to ANS imbalance model rats to elucidate its effects.

Results

30 Hz and 100 Hz iaES clearly affected HRV and HR in normal rats. 30 Hz iaES increased HRV, and decreased HR. 100 Hz iaES decreased HRV, and increased HR. In sympathetic excited state rats, 30 Hz iaES increased HRV. 100 Hz iaES increased HRV, and decreased HR. In parasympathetic excited state rats, 30 Hz and 100 Hz iaES decreased HRV. In sympathetic inhibited state rats, 30 Hz iaES decreased HRV, while 100 Hz iaES decreased HR. In parasympathetic inhibited rats, 30 Hz iaES decreased HR and 100 Hz iaES increased HRV.

Conclusion

30 Hz and 100 Hz iaES contribute to ANS rebalance by increasing vagal and sympathetic activity with different amplifications. The 30 Hz iaES exhibited positive effects in all the imbalanced states. 100 Hz iaES suppressed the sympathetic arm in sympathetic excitation and sympathetic/parasympathetic inhibition and suppressed the vagal arm and promoted the sympathetic arm in parasympathetic excitation and normal states.

Educating the next generation of psychiatrists in the use of clinical neuromodulation therapies: what should all psychiatry residents know?

A variety of neuromodulation treatments are available today and more are on the way, but are tomorrow's psychiatrists prepared to incorporate these tools into their patients' care plans? This article addresses the need for training in clinical neuromodulation for general psychiatry trainees. To ensure patient access to neuromodulation treatments, we believe that general psychiatrists should receive adequate education in a spectrum of neuromodulation modalities to identify potential candidates and integrate neuromodulation into their multidisciplinary care plans. We propose curricular development across the four FDA-cleared modalities currently available in psychiatric practice: electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). With a focus on psychiatry residency training, the article delineates core learning components for each neuromodulation technique. For each modality, we review the clinical training status, the respective FDA-cleared indications, mechanisms of action, clinical indications and contraindications, adverse effects, informed consent process, dosing considerations, and clinical management guidelines. The approach outlined in this article aims to contribute to the development of a well-rounded generation of psychiatry trainees with the capacity to navigate the growing field of neuromodulation. Whether or not a psychiatrist specializes in delivering neuromodulation therapies themselves, it is incumbent on all psychiatrists to be able to identify patients who should be referred to neuromodulation therapies, and to provide comprehensive patient care before, during and after clinical neuromodulation interventions to optimize outcomes and prevent relapse.

Label-Free Functional Imaging of Vagus Nerve Stimulation-Evoked Potentials at the Cortical Surface

Vagus Nerve Stimulation (VNS) was the first FDA-approved stimulation therapy to treat patients with refractory epilepsy and remains widely used. The mechanisms behind the therapeutic effect of VNS remain unknown but are thought to involve afferent-mediated modulation to cortical circuits 1. In this work, we use a coherent holographic imaging system to characterize vagus nerve evoked potentials (VEPs) in the cortex in response to typical VNS stimulation paradigms, which does not require electrode placement nor any genetic, structural, or functional labels. We find that stimulation amplitude strongly modulates VEPs response magnitude (effect size 0.401), while pulse width has a moderate modulatory effect (effect size 0.127) and frequency has almost no modulatory effect (effect size 0.009) on the evoked potential magnitude. We find mild interaction between pulse width and frequency. This non-contact label-free functional imaging technique could serve as a non-invasive rapid feedback tool to quantify VEPs and could increase the efficacy of VNS in patients with refractory epilepsy.

Self-administered non-invasive vagus nerve stimulation therapy for severe pharmacoresistant restless legs syndrome: outcomes at 6 months

Severe pharmacoresistant restless legs syndrome (RLS) is difficult to manage and a source of suffering to patients. We studied the effectiveness at 6 months of an innovative treatment: transauricular vagus nerve stimulation (taVNS) in the left cymba concha in a case series of 15 patients, 53% male, mean (SD) age 62.7 (12.3) years with severe pharmacoresistant RLS (mean [SD] International Restless Legs Rating Scale [IRLS] score of 31.9 [2.9]) at baseline. Following an 8-week non-randomised hospital-based study with eight 1-h sessions of taVNS, patients were trained to administer taVNS at home and were followed up for 6 months. The primary outcome measure was the IRLS score, secondary outcome measures were quality of life, mood disorders using the Hospital Anxiety and Depression scale (HAD) subscales for depression (HADD) and anxiety (HADA). At the 6-month follow-up 13/15 patients continued to use weekly taVNS. Symptom severity decreased (mean [SD] IRLS score 22.2 [9.32] at 6 months, p = 0.0005). Four of the 15 patients had an IRLS score of <20 at 6 months and two an IRLS score of 5. Quality of life significantly improved compared to baseline (mean [SD] score at baseline 49.3 [18.1] versus 65.66 [22.58] at 6 months, p = 0.0005) as did anxiety and depression symptoms (mean [SD] HADA score at baseline 8.9 [5.4] versus 7.53 [4.42] at 6 months, p = 0.029; and HADD score at baseline 5.2 [4.5] versus 4.73 [4.44] at 6 months, p = 0.03). Treatment was well tolerated, and no adverse events were reported. Our case series shows a potential role for self-administered taVNS in patients with severe pharmacoresistant RLS. Randomised controlled trials are needed to confirm the utility of taVNS.

Preventive noninvasive vagal nerve stimulation reduces insufficient sleep-induced depression by improving the autonomic nervous system

BACKGROUND

Depression is closely linked to an imbalance in the autonomic nervous system (ANS). However, the role of this imbalance in mediating the effects of sleep deprivation (SD) and vagus nerve stimulation (VNS) on emotional well-being is not fully understood.

METHODS

A population-based analysis was conducted to explore the relationship between sleep duration, depression scores, and heart rate variability (HRV). Additionally, the chronic SD mouse model was established to assess the impact of preventive transcutaneous auricular VNS (taVNS) on pathological and behavioral changes.

RESULTS

Our study found a significant link between sleep duration, depression severity, and HRV. Shorter sleep duration was associated with higher depression scores and lower RMSSD (a measure of HRV). In our rat model, insufficient sleep consistently impaired HRV. This effect was mitigated by taVNS, accompanied by corresponding changes in levels of IL-1β and IL-6, astrocyte and microglia activation, and tail suspension times.

CONCLUSIONS

Using VNS as a preventive treatment for depression-risk individuals with insufficient sleep shows promise. It not only broadens the potential applications of VNS but also sheds light on its mechanism-particularly its role in enhancing vagal nerve function and balancing the ANS, as evidenced by HRV measurements.

Traumatic Brain Injury and Neuromodulation Techniques in Rehabilitation: A Scoping Review

BACKGROUND AND OBJECTIVES

Traumatic Brain Injury (TBI) is a condition in which an external force, usually a violent blow to the head, causes functional impairment in the brain. Neuromodulation techniques are thought to restore altered function in the brain, resulting in improved function and reduced symptoms. Brain stimulation can alter the firing of neurons, boost synaptic strength, alter neurotransmitters and excitotoxicity, and modify the connections in their neural networks. All these are potential effects on brain activity. Accordingly, this is a promising therapy for TBI. These techniques are flexible because they can target different brain areas and vary in frequency and amplitude. This review aims to investigate the recent literature about neuromodulation techniques used in the rehabilitation of TBI patients.

MATERIALS AND METHODS

The identification of studies was made possible by conducting online searches on PubMed, Web of Science, Cochrane, Embase, and Scopus databases. Studies published between 2013 and 2023 were selected. This review has been registered on OSF (JEP3S).

RESULTS

We have found that neuromodulation techniques can improve the rehabilitation process for TBI patients in several ways. Transcranial Magnetic Stimulation (TMS) can improve cognitive functions such as recall ability, neural substrates, and overall improved performance on neuropsychological tests. Repetitive TMS has the potential to increase neural connections in many TBI patients but not in all patients, such as those with chronic diffuse axonal damage.

CONCLUSIONS

This review has demonstrated that neuromodulation techniques are promising instruments in the rehabilitation field, including those affected by TBI. The efficacy of neuromodulation can have a significant impact on their lives and improve functional outcomes for TBI patients.

Transcutaneous auricular vagus nerve stimulation alters cough sensitivity depending on stimulation parameters: potential implications for aspiration risk

Background

Transcutaneous auricular vagus nerve stimulation (taVNS) is considered a safe and promising tool for limb rehabilitation after stroke, but its effect on cough has never been studied. It is known that the ear and larynx share vagal afferent pathways, suggesting that stimulating the ear with taVNS might have effects on cough sensitivity. The specific stimulation parameters used can influence outcomes.

Objective

To investigate the effect of various stimulation parameters on change in cough sensitivity, compared to the reference parameter of 25 Hz stimulation at the left concha (most commonly-used parameter for stroke rehabilitation). Design, setting, and participants: Randomized, single-blind, active-controlled, eight-period cross-over design conducted March to August 2022 at a New Zealand research laboratory with 16 healthy participants.

Interventions

All participants underwent eight stimulation conditions which varied by stimulation side (right ear, left ear), zone (ear canal, concha), and frequency (25 Hz, 80 Hz). Main outcome measures: Change in natural and suppressed cough threshold (from baseline to after 10 min of stimulation) assessed using a citric acid cough reflex test.

Results

When compared to the reference parameter of 25 Hz stimulation at the left concha, there was a reduction in natural cough threshold of -0.16 mol/L for 80 Hz stimulation at the left canal (p = 0.004), indicating increased sensitivity. For the outcome measure of suppressed cough threshold, there was no significant effect of any of the stimulation conditions compared to the active reference.

Conclusion

Since stroke patients often have cough hyposensitivity with resulting high risk of silent aspiration, using 80 Hz taVNS at the left canal may be a better choice for future stroke rehabilitation studies than the commonly used 25 Hz taVNS at the left concha. Treatment parameters should be manipulated in future sham-controlled trials to maximize any potential treatment effect of taVNS in modulating cough sensitivity.

Clinical trial registration

ACTRN12623000128695.

Transcriptional response of the heart to vagus nerve stimulation

Heart failure is a major clinical problem, with treatments involving medication, devices, and emerging neuromodulation therapies such as vagus nerve stimulation (VNS). Considering the ongoing interest in using VNS to treat cardiovascular disease, it is important to understand the genetic and molecular changes developing in the heart in response to this form of autonomic neuromodulation. This experimental animal (rat) study investigated the immediate transcriptional response of the ventricular myocardium to selective stimulation of vagal efferent activity using an optogenetic approach. Vagal preganglionic neurons in the dorsal motor nucleus of the vagus nerve were genetically targeted to express light-sensitive chimeric channelrhodopsin variant ChIEF and stimulated using light. RNA sequencing of the left ventricular myocardium identified 294 differentially expressed genes (false discovery rate < 0.05). Qiagen Ingenuity Pathway Analysis (IPA) highlighted 118 canonical pathways that were significantly modulated by vagal activity, of which 14 had a z score of ≥2/≤-2, including EIF-2, IL-2, integrin, and NFAT-regulated cardiac hypertrophy. IPA revealed the effect of efferent vagus stimulation on protein synthesis, autophagy, fibrosis, autonomic signaling, inflammation, and hypertrophy. IPA further predicted that the identified differentially expressed genes were the targets of 50 upstream regulators, including transcription factors (e.g., MYC and NRF1) and microRNAs (e.g., miR-335-3p and miR-338-3p). These data demonstrate that the vagus nerve has a major impact on the myocardial expression of genes involved in the regulation of key biological pathways. The transcriptional response of the ventricular myocardium induced by stimulation of vagal efferents is consistent with the beneficial effect of maintained/increased vagal activity on the heart.NEW & NOTEWORTHY This experimental animal study investigated the immediate transcriptional response of the ventricular myocardium to selective stimulation of vagal efferent activity. Vagal stimulation induced significant transcriptional changes in the heart involving the pathways controlling autonomic signaling, inflammation, fibrosis, and hypertrophy. This study provides the first direct evidence that myocardial gene expression is modulated by the activity of the autonomic nervous system.

Analgesic Effects of Vagus Nerve Stimulation on Visceral Hypersensitivity: A Direct Comparison Between Invasive and Noninvasive Methods in Rats

OBJECTIVES

The aims of this study were to investigate analgesic effects of vagus nerve stimulation (VNS) on visceral hypersensitivity (VH) in a rodent model of functional dyspepsia (FD) and to compare invasive VNS with noninvasive auricular VNS (aVNS).

MATERIALS AND METHODS

Eighteen ten-day-old male rats were gavaged with 0.1% iodoacetamide (IA) or 2% sucrose solution for six days. After eight weeks, IA-treated rats were implanted with electrodes for VNS or aVNS (n = 6 per group). Different parameters, varying in frequency and stimulation duty cycle, were tested to find the best parameter based on the improvement of VH assessed by electromyogram (EMG) during gastric distension.

RESULTS

Compared with sucrose-treated rats, visceral sensitivity was increased significantly in IA-treated "FD" rats and ameliorated remarkably by VNS (at 40, 60, and 80 mm Hg; p ≤ 0.02, respectively) and aVNS (at 60 and 80 mm Hg; p ≤ 0.05, respectively) with the parameter of 100 Hz and 20% duty cycle. There was no significant difference in area under the curve of EMG responses between VNS and aVNS (at 60 and 80 mm Hg, both p > 0.05). Spectral analysis of heart rate variability revealed a significant enhancement in vagal efferent activity while applying VNS/aVNS compared with sham stimulation (p < 0.01). In the presence of atropine, no significant differences were noted in EMG after VNS/aVNS. Naloxone blocked the analgesic effects of VNS/aVNS.

CONCLUSIONS

VNS/aVNS with optimized parameter elicits ameliorative effects on VH, mediated by autonomic and opioid mechanisms. aVNS is as effective as direct VNS and has great potential for treating visceral pain in patients with FD.

Preliminary evidence of transcutaneous vagus nerve stimulation effects on sleep in veterans with post-traumatic stress disorder

Sleep problems are common among veterans with post-traumatic stress disorder and closely associated with hyperarousal symptoms. Transcutaneous vagus nerve stimulation (tVNS) may have potential to improve sleep quality in veterans with PTSD through effects on brain systems relevant to hyperarousal and sleep-wake regulation. The current pilot study examines the effect of 1 h of tVNS administered at "lights out" on sleep architecture, microstructure, and autonomic activity. Thirteen veterans with PTSD completed two nights of laboratory-based polysomnography during which they received 1 h of either active tVNS (tragus) or sham stimulation (earlobe) at "lights out" with randomised order. Sleep staging and stability metrics were derived from polysomnography data. Autonomic activity during sleep was assessed using the Porges-Bohrer method for calculating respiratory sinus arrhythmia (RSAP-B ). Paired t-tests revealed a small decrease in the total sleep time (d = -0.31), increase in N3 sleep (d = 0.23), and a small-to-moderate decrease in REM sleep (d = -0.48) on nights of active tVNS relative to sham stimulation. tVNS was also associated with a moderate reduction in cyclic alternating pattern (CAP) rate (d = -0.65) and small-to-moderate increase in RSAP-B during NREM sleep. Greater NREM RSAP-B was associated with a reduced CAP rate and NREM alpha power. This pilot study provides preliminary evidence that tVNS may improve sleep depth and stability in veterans with PTSD, as well as increase parasympathetically mediated nocturnal autonomic activity. These results warrant continued investigation into tVNS as a potential tool for treating sleep disturbance in veterans with PTSD.

Vagus nerve stimulation in medically refractory epilepsy: Adverse effects and clinical correlates

OBJECTIVES

To assess the frequency of adverse effects among pediatric and adult patients and the clinical variables associated with a higher probability of developing side effects.

METHODS

This retrospective study enrolled pediatric and adult patients who underwent Vagus nerve stimulation (VNS) implantation at our institution and had documented follow-up during clinic visits for at least 6 months after implantation. Data collected included demographic information, epilepsy diagnosis, and device data.

RESULTS

A total of 43 patients with drug-resistant epilepsy who received a VNS device at our institution were enrolled. The median follow-up period was 12 months. Fourteen patients (32.55%) reported no side effects from VNS therapy. Side effects ranged from mild to severe, with significant side effects observed in 8 patients. Data on therapy efficacy were collected, and 10 patients (23.26%) reported no change in seizure frequency following device implantation.

CONCLUSION

This study demonstrates that VNS is an important adjunct treatment option for epilepsy patients. Dysphagia and dyspnea can be significant adverse effects leading to treatment discontinuation, aspiration pneumonia, intensive care unit (ICU) admission, and prolonged hospital stay. These effects are more frequent in patients with symptomatic generalized epilepsy, global developmental delay at baseline, previous ICU admissions, abnormal brain magnetic resonance imaging findings, and seizures with multiple semiologies.

Acute Effect of Transcutaneous Auricular Vagus Nerve Stimulation on Hand Tremor in Parkinson's Disease: A Pilot Study of Case Series

Objectives

The aim of this study is to investigate the effects of non-invasive vagus nerve stimulation (VNS) on tremor in Parkinson's disease (PD).

Methods

This single-center, prospective, and implementation study with before-after design included five participants diagnosed with PD. Auricular VNS was applied to each participant 3 times on different days. VNS was applied to the participants as the right ear, left ear, and bilateral ear. The cardiovascular parameters of the participants were evaluated with Kubios HRV Standard and tremor with UPDRS tremor subscale and smartphone application before and after the intervention.

Results

Significant decrease in diastolic blood pressure (p=0.043) was found in participants who underwent bilateral auricular VNS. Although there was no significant change in the UPDRS tremor subscale, decreases in the maximum tremor amplitude in the x (p=0.043) and y (0.014) planes were detected in the measurements made with the smartphone application.

Conclusion

In this study, a decrease in the tremor amplitude measured in the 3D plane with auricular VNS was found in patients with PD.

Transcutaneous auricular vagus nerve stimulation in the treatment of disorders of consciousness: mechanisms and applications

This review provides an in-depth exploration of the mechanisms and applications of transcutaneous auricular vagus nerve stimulation (taVNS) in treating disorders of consciousness (DOC). Beginning with an exploration of the vagus nerve's role in modulating brain function and consciousness, we then delve into the neuroprotective potential of taVNS demonstrated in animal models. The subsequent sections assess the therapeutic impact of taVNS on human DOC, discussing the safety, tolerability, and various factors influencing the treatment response. Finally, the review identifies the current challenges in taVNS research and outlines future directions, emphasizing the need for large-scale trials, optimization of treatment parameters, and comprehensive investigation of taVNS's long-term effects and underlying mechanisms. This comprehensive overview positions taVNS as a promising and safe modality for DOC treatment, with a focus on understanding its intricate neurophysiological influence and optimizing its application in clinical settings.

Neuropsychiatric Lyme Disease and Vagus Nerve Stimulation

Lyme disease, the most common tick-borne disease in the United States, is caused by infection with the spirochete Borrelia burgdorferi. While most patients with acute Lyme disease recover completely if treated with antibiotics shortly after the onset of infection, approximately 10-30% experience post-treatment symptoms and 5-10% have residual symptoms with functional impairment (post-treatment Lyme disease syndrome or PTLDS). These patients typically experience pain, cognitive problems, and/or fatigue. This narrative review provides a broad overview of Lyme disease, focusing on neuropsychiatric manifestations and persistent symptoms. While the etiology of persistent symptoms remains incompletely understood, potential explanations include persistent infection, altered neural activation, and immune dysregulation. Widely recognized is that new treatment options are needed for people who have symptoms that persist despite prior antibiotic therapy. After a brief discussion of treatment approaches, the article focuses on vagus nerve stimulation (VNS), a neuromodulation approach that is FDA-approved for depression, epilepsy, and headache syndromes and has been reported to be helpful for other diseases characterized by inflammation and neural dysregulation. Transcutaneous VNS stimulates the external branch of the vagus nerve, is minimally invasive, and is well-tolerated in other conditions with few side effects. If well-controlled double-blinded studies demonstrate that transcutaneous auricular VNS helps patients with chronic syndromes such as persistent symptoms after Lyme disease, taVNS will be a welcome addition to the treatment options for these patients.

Short-term transcutaneous vagus nerve stimulation increases pupil size but does not affect EEG alpha power: A replication of Sharon et al. (2021, Journal of Neuroscience)

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (taVNS) has been tested as a potential treatment for pharmaco-resistant epilepsy and depression. Its clinical efficacy is thought to depend on taVNS-induced activation of the locus coeruleus and other neuromodulator systems. However, unlike for invasive VNS in rodents, there is little evidence for an effect of taVNS on noradrenergic activity.

OBJECTIVE

We attempted to replicate recently published findings by Sharon et al. (2021), showing that short bursts of taVNS transiently increased pupil size and decreased EEG alpha power, two correlates of central noradrenergic activity.

METHODS

Following the original study, we used a single-blind, sham-controlled, randomized cross-over design. Human volunteers (n = 29) received short-term (3.4 s) taVNS at the maximum level below the pain threshold, while we collected resting-state pupil-size and EEG data. To analyze the data, we used scripts provided by Sharon and colleagues.

RESULTS

Consistent with Sharon et al. (2021), pupil dilation was significantly larger during taVNS than during sham stimulation (p = .009; Bayes factor supporting the difference = 7.45). However, we failed to replicate the effect of taVNS on EEG alpha power (p = .37); the data were four times more likely under the null hypothesis (BF10 = 0.28).

CONCLUSION

Our findings support the effectiveness of short-term taVNS in inducing transient pupil dilation, a correlate of phasic noradrenergic activity. However, we failed to replicate the recent finding by Sharon et al. (2021) that taVNS attenuates EEG alpha activity. Overall, this study highlights the need for continued research on the neural mechanisms underlying taVNS efficacy and its potential as a treatment option for pharmaco-resistant conditions. It also highlights the need for direct replications of influential taVNS studies.

Left or right ear? A neuroimaging study using combined taVNS/fMRI to understand the interaction between ear stimulation target and lesion location in chronic stroke

BACKGROUND

Implanted vagus nerve stimulation (VNS) and transcutaneous auricular VNS (taVNS) have been primarily administered clinically to the unilateral-left vagus nerve. This left-only convention has proved clinically beneficial in brain disorders. However, in stroke survivors, the presence of a lesion in the brain may complicate VNS-mediated signaling, and it is important to understand the laterality effects of VNS in stroke survivors to optimize the intervention.

OBJECTIVE

To understand whether taVNS delivered to different ear targets relative to the lesion (ipsilesional vs contralesional vs bilateral vs sham) impacts blood oxygenation level dependent (BOLD) signal propagation in stroke survivors.

METHODS

We enrolled 20 adults with a prior history of stroke. Each participant underwent a single visit, during which taVNS was delivered concurrently during functional magnetic resonance imaging (fMRI) acquisition. Each participant received three discrete active stimulation conditions (ipsilesional, contralesional, bilateral) and one sham condition in a randomized order. Stimulation-related BOLD signal changes in the active conditions were compared to sham conditions to understand the interaction taVNS and laterality effects.

RESULTS

All active taVNS conditions deactivated the contralesional default mode network related regions compared to sham, however only ipsilesional taVNS enhanced the activations in the ipsilesional visuomotor and secondary visual cortex. Furthermore, we reveal an interaction in task activations between taVNS and cortical visuomotor areas, where ipsilesional taVNS significantly increased ipsilesional visuomotor activity and decreased contralesional visuomotor activity compared to sham.

CONCLUSION

Laterality of taVNS relative to the lesion is a critical factor in optimizing taVNS in a stroke population, with ipsilesional stimulation providing largest direct brain activation and should be explored further when designing taVNS studies in neurorehabilitation.

Motor Activated Auricular Vagus Nerve Stimulation as a Potential Neuromodulation Approach for Post-Stroke Motor Rehabilitation: A Pilot Study

BACKGROUND

Implanted vagus nerve stimulation (VNS), when synchronized with post-stroke motor rehabilitation improves conventional motor rehabilitation training. A non-invasive VNS method known as transcutaneous auricular vagus nerves stimulation (taVNS) has emerged, which may mimic the effects of implanted VNS.

OBJECTIVE

To determine whether taVNS paired with motor rehabilitation improves post-stroke motor function, and whether synchronization with movement and amount of stimulation is critical to outcomes.

METHODS

We developed a closed-loop taVNS system for motor rehabilitation called motor activated auricular vagus nerve stimulation (MAAVNS) and conducted a randomized, double-blind, pilot trial investigating the use of MAAVNS to improve upper limb function in 20 stroke survivors. Participants attended 12 rehabilitation sessions over 4-weeks, and were assigned to a group that received either MAAVNS or active unpaired taVNS concurrently with task-specific training. Motor assessments were conducted at baseline, and weekly during rehabilitation training. Stimulation pulses were counted for both groups.

RESULTS

A total of 16 individuals completed the trial, and both MAAVNS (n = 9) and unpaired taVNS (n = 7) demonstrated improved Fugl-Meyer Assessment upper extremity scores (Mean ± SEM, MAAVNS: 5.00 ± 1.02, unpaired taVNS: 3.14 ± 0.63). MAAVNS demonstrated greater effect size (Cohen's d = 0.63) compared to unpaired taVNS (Cohen's d = 0.30). Furthermore, MAAVNS participants received significantly fewer stimulation pulses (Mean ± SEM, MAAVNS: 36 070 ± 3205) than the fixed 45 000 pulses unpaired taVNS participants received (P < .05).

CONCLUSION

This trial suggests stimulation timing likely matters, and that pairing taVNS with movements may be superior to an unpaired approach. Additionally, MAAVNS effect size is comparable to that of the implanted VNS approach.

Application of Vagus Nerve Stimulation in Spinal Cord Injury Rehabilitation

Spinal cord injury (SCI) is a prevalent devastating condition causing significant morbidity and mortality, especially in developing countries. The pathophysiology of SCI involves ischemia, neuroinflammation, cell death, and scar formation. Due to the lack of definitive therapy for SCI, interventions mainly focus on rehabilitation to reduce deterioration and improve the patient's quality of life. Currently, rehabilitative exercises and neuromodulation methods such as functional electrical stimulation, epidural electrical stimulation, and transcutaneous electrical nerve stimulation are being tested in patients with SCI. Other spinal stimulation techniques are being developed and tested in animal models. However, often these methods require complex surgical procedures and solely focus on motor function. Vagus nerve stimulation (VNS) is currently used in patients with epilepsy, depression, and migraine and is being investigated for its application in other disorders. In animal models of SCI, VNS significantly improved locomotor function by ameliorating inflammation and improving plasticity, suggesting its use in human subjects. SCI patients also suffer from nonmotor complications, including pain, gastrointestinal dysfunction, cardiovascular disorders, and chronic conditions such as obesity and diabetes. VNS has shown promising results in alleviating these conditions in non-SCI patients, which makes it a possible therapeutic option in SCI patients.

Limited output transcranial electrical stimulation 2023 (LOTES-2023): Updates on engineering principles, regulatory statutes, and industry standards for wellness, over-the-counter, or prescription devices with low risk

The objective and scope of this Limited Output Transcranial Electrical Stimulation 2023 (LOTES-2023) guidance is to update the previous LOTES-2017 guidance. These documents should therefore be considered together. The LOTES provides a clearly articulated and transparent framework for the design of devices providing limited output (specified low-intensity range) transcranial electrical stimulation for a variety of intended uses. These guidelines can inform trial design and regulatory decisions, but most directly inform manufacturer activities - and hence were presented in LOTES-2017 as "Voluntary industry standard for compliance controlled limited output tES devices". In LOTES-2023 we emphasize that these standards are largely aligned across international standards and national regulations (including those in USA, EU, and South Korea), and so might be better understood as "Industry standards for compliance controlled limited output tES devices". LOTES-2023 is therefore updated to reflect a consensus among emerging international standards, as well as best available scientific evidence. "Warnings" and "Precautions" are updated to align with current biomedical evidence and applications. LOTES standards applied to a constrained device dose range, but within this dose range and for different use-cases, manufacturers are responsible to conduct device-specific risk management.

Noradrenergic α1, α2, and β1receptors mediate VNS-induced theta oscillations

Although vagal nerve stimulation (VNS) has been employed with success for almost four decades in many central nervous system disturbances, the physiological and pharmacological processes underlying this therapy are still unclear. Searching for central mechanisms of VNS is clinically limited. Hence, in many experiments, VNS technique is tested on the model of laboratory animals. In the present study we proceed with the experiments to verify some central effects of VNS. Specifically, we focussed on the hippocampal formation (HPC) noradrenergic profile which underlines the VNS-induced theta oscillations in anesthetized rats (Broncel et al., 2017; 2021). The effects of noradrenaline (NE) and selective noradrenergic α and β agonists and antagonists were tested in experiments organized in three stages. Initially, a nonspecific noradrenergic agonist, noradrenaline, was administrated. In the second stage, noradrenergic α and β agonists were applied. In the last stage, the administration of selected agonists was pretreated by specific antagonists. The results of the present study provide evidence that the selective activation of HPC α1, α2, and β1 noradrenergic receptors produce the inhibition of VNS-induced theta oscillations. Hippocampal β2 and β3 receptors were found not to be involved in the modulation of oscillations produced by the vagal nerve stimulation. The obtained outcomes are discussed in light of the effects of increased exogenous NE and induced release of endogenous NE.

Vagus innervation in the gastrointestinal tumor: Current understanding and challenges

The vagus nerve (VN) is the main parasympathetic nerve of the autonomic nervous system. It is widely distributed in the gastrointestinal tract and maintains gastrointestinal homeostasis with the sympathetic nerve under physiological conditions. The VN communicates with various components of the tumor microenvironment to positively and dynamically affect the progression of gastrointestinal tumors (GITs). The intervention in vagus innervation delays GIT progression. Developments in adeno-associated virus vectors, nanotechnology, and in vivo neurobiological techniques have enabled the creation of precisely regulated "tumor neurotherapies". Furthermore, the combination of neurobiological techniques and single cell sequencing may reveal more insights into VN and GIT. The present review aimed to summarize the mechanisms of communication between the VN and the gastrointestinal TME and to explore the potential and challenges of VN-based tumor neurotherapy in GITs.

Epileptic-network-based prediction and control of seizures in humans

Epilepsy is now conceptualized as a network disease. The epileptic brain network comprises structurally and functionally connected cortical and subcortical brain regions - spanning lobes and hemispheres -, whose connections and dynamics evolve in time. With this concept, focal and generalized seizures as well as other related pathophysiological phenomena are thought to emerge from, spread via, and be terminated by network vertices and edges that also generate and sustain normal, physiological brain dynamics. Research over the last years has advanced concepts and techniques to identify and characterize the evolving epileptic brain network and its constituents on various spatial and temporal scales. Network-based approaches further our understanding of how seizures emerge from the evolving epileptic brain network, and they provide both novel insights into pre-seizure dynamics and important clues for success or failure of measures for network-based seizure control and prevention. In this review, we summarize the current state of knowledge and address several important challenges that would need to be addressed to move network-based prediction and control of seizures closer to clinical translation.

Measuring and modeling the effects of vagus nerve stimulation on heart rate and laryngeal muscles

BACKGROUND

Reduced heart rate (HR) during vagus nerve stimulation (VNS) is associated with therapy for heart failure, but stimulation frequency and amplitude are limited by patient tolerance. An understanding of physiological responses to parameter adjustments would allow differential control of therapeutic and side effects. To investigate selective modulation of the physiological responses to VNS, we quantified the effects and interactions of parameter selection on two physiological outcomes: one related to therapy (reduced HR) and one related to side effects (laryngeal muscle EMG).

METHODS

We applied a broad range of stimulation parameters (mean pulse rates (MPR), intra-burst frequencies, and amplitudes) to the vagus nerve of anesthetized mice. We leveraged the in vivo recordings to parameterize and validate computational models of HR and laryngeal muscle activity across amplitudes and temporal patterns of VNS. We constructed a finite element model of excitation of fibers within the mouse cervical vagus nerve.

RESULTS

HR decreased with increased amplitude, increased MPR, and decreased intra-burst frequency. EMG increased with increased MPR. Preferential HR effects over laryngeal EMG effects required combined adjustments of amplitude and MPR. The model of HR responses highlighted contributions of ganglionic filtering to VNS-evoked changes in HR at high stimulation frequencies. Overlap in activation thresholds between small and large modeled fibers was consistent with the overlap in dynamic ranges of related physiological measures (HR and EMG).

CONCLUSION

The present study provides insights into physiological responses to VNS required for informed parameter adjustment to modulate selectively therapeutic effects and side effects.

Effect of transcutaneous auricular vagus nerve stimulation on post-stroke dysphagia

BACKGROUND AND PURPOSE

It has been proved that electrical vagus nerve stimulation can promote the recovery of motor function after stroke. There were no trials on the use of transcutaneous auricular electrical vagus nerve stimulation (ta-VNS) in patients with dysphagia after acute stroke. Our aim was to confirm whether ta-VNS can promote the recovery of swallowing function in these acute stroke patients with dysphagia.

METHODS

We conducted a sham-controlled, double-blinded, parallel pilot study in 40 acute stroke patients randomly assigned to receive ta-VNS or sham ta-VNS combined with conventional rehabilitation training. The intensity of ta-VNS treatment was adjusted according to the patient's tolerance, 30 min each time, twice a day, five times a week, with a total course of 3 weeks. In the sham group, the parameters were the same except energy output. Swallowing function was assessed with Modified Mann assessment of swallowing ability (MASA), functional communication measure swallowing test (FCM), and the Rosenbek leakage/aspiration scale (RAS) according to swallowing video fluoroscopic (SVF) before the intervention (baseline, T0), immediately after the intervention (T1) and 4 weeks after the intervention (T2).

RESULTS

After treatment, ta-VNS group statistically and clinically had larger change of MASA, FCM, and RAS scores compared with control group (P < 0.05) and this improvement continued at least 4 weeks after the end of treatment. There were no serious adverse events occurred during the whole intervention.

CONCLUSION

The transcutaneous auricular electrical vagus nerve stimulation is effective as a novel and noninvasive treatment strategy for patients with dysphagia after acute stroke.

TRIAL REGISTRATION

No: kelunshen No. 63 in 2020.

Optimization of respiratory-gated auricular vagus afferent nerve stimulation for the modulation of blood pressure in hypertension

Background

The objective of this pilot study was to identify frequency-dependent effects of respiratory-gated auricular vagus afferent nerve stimulation (RAVANS) on the regulation of blood pressure and heart rate variability in hypertensive subjects and examine potential differential effects by sex/gender or race.

Methods

Twenty hypertensive subjects (54.55 ± 6.23 years of age; 12 females and 8 males) were included in a within-person experimental design and underwent five stimulation sessions where they received RAVANS at different frequencies (i.e., 2 Hz, 10 Hz, 25 Hz, 100 Hz, or sham stimulation) in a randomized order. EKG and continuous blood pressure signals were collected during a 10-min baseline, 30-min stimulation, and 10-min post-stimulation periods. Generalized estimating equations (GEE) adjusted for baseline measures were used to evaluate frequency-dependent effects of RAVANS on heart rate, high frequency power, and blood pressure measures, including analyses stratified by sex and race.

Results

Administration of RAVANS at 100 Hz had significant overall effects on the reduction of heart rate (β = -2.03, p = 0.002). It was also associated with a significant reduction of diastolic (β = -1.90, p = 0.01) and mean arterial blood pressure (β = -2.23, p = 0.002) in Black hypertensive participants and heart rate in female subjects (β = -2.83, p = 0.01) during the post-stimulation period when compared to sham.

Conclusion

Respiratory-gated auricular vagus afferent nerve stimulation exhibits frequency-dependent rapid effects on the modulation of heart rate and blood pressure in hypertensive patients that may further differ by race and sex. Our findings highlight the need for the development of optimized stimulation protocols that achieve the greatest effects on the modulation of physiological and clinical outcomes in this population.

The Role of Short Chain Fatty Acids in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is characterized by abdominal pain and disordered bowel habits. The etiology of IBS is multifactorial, including abnormal gut-brain interactions, visceral hypersensitivity, altered colon motility, and psychological factors. Recent studies have shown that the intestinal microbiota and its metabolites short chain fatty acids (SCFAs) may be involved in the pathogenesis of IBS. SCFAs play an important role in the pathophysiology of IBS. We discuss the underlying mechanisms of action of SCFAs in intestinal inflammation and immunity, intestinal barrier integrity, motility, and the microbiota-gut-brain axis. Limited to previous studies, further studies are required to investigate the mechanisms of action of SCFAs in IBS and provide more precise therapeutic strategies for IBS.

Timing of vagus nerve stimulation during fear extinction determines efficacy in a rat model of PTSD

Studies have indicated that vagus nerve stimulation (VNS) enhances extinction learning in rodent models. Here, we investigated if pairing VNS with the conditioned stimulus is required for the enhancing effects of VNS. Adult Sprague-Dawley rats were exposed to intense stress followed by fear conditioning training to produce resistant fear. Rats were then implanted with a cuff electrode around the left vagus. After recovery, rats underwent extinction training paired with VNS (0.5 s, 0.8 mA, 100 µs, and 30 Hz) or with Sham VNS (0 mA). VNS rats were randomized into the following subgroups: During VNS (delivered during presentations of the conditioned stimulus, CS), Between VNS (delivered between CS presentations), Continuous VNS (delivered during the entire extinction session), and Dispersed VNS (delivered at longer inter-stimulation intervals across the extinction session). Sham VNS rats failed to extinguish the conditioned fear response over 5 days of repeated exposure to the CS. Rats that received Between or Dispersed VNS showed modest improvement in conditioned fear at the retention test. During and Continuous VNS groups displayed the greatest reduction in conditioned fear. These findings indicate that delivering VNS paired precisely with CS presentations or continuously throughout extinction promotes the maximum enhancement in extinction learning.

Electroencephalographic Patterns in taVNS: A Systematic Review

Transcutaneous auricular vagus nerve stimulation (taVNS) is a newer delivery system using a non-invasive stimulation device placed at the ear. taVNS research is focused on clinical trials showing potential therapeutic benefits, however the neurophysiological effects of this stimulation on brain activity are still unclear. We propose a systematic review that aims to describe the effects of taVNS on EEG measures and identify taVNS parameters that can potentially lead to consistent EEG-mediated biomarkers for this therapy. A systematic literature review was carried out following the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes (PRISMA) and the Cochrane handbook for systematic reviews. Clinical trials examining EEG parameters were considered, including absolute and relative power, coherence, degree of symmetry, evoked potentials, and peak frequency of all bands. According to our criteria, 18 studies (from 122 articles) were included. Our findings show a general trend towards increased EEG power spectrum activity in lower frequencies, and changes on early components of the ERP related to inhibitory tasks. This review suggests that quantitative electroencephalography can be used to assess the effects of taVNS on brain activity, however more studies are needed to systematically establish the specific effects and metrics that would reflect the non-invasive stimulation through the auricular branch of the vagus nerve.

Rapid titration of VNS therapy reduces time-to-response in epilepsy

BACKGROUND

Common titration strategies for vagus nerve stimulation (VNS) prioritize monitoring of tolerability during small increases in stimulation intensity over several months. Prioritization of tolerability is partially based on how quickly side effects can be perceived and reported by patients, and the delayed onset of clinical benefits from VNS. However, many practices assess the clinical benefit of VNS at one year after implantation, and excessive caution during the titration phase can significantly delay target dosing or prevent a patient from reaching a therapeutic dose entirely.

OBJECTIVE

This study aimed to characterize the relationship between titration speed and the onset of clinical response to VNS.

METHODS

To assess differences between more aggressive titration strategies and more conservative ones, we analyzed the relationship between time-to-dose and time-to-response using a weighted Cox regression. The target dose was empirically defined as 1.625 mA output current delivered at 250 microsecond pulse widths at 20 Hz. Patient-level outcomes and dosing data were segregated into fast (<3 months), medium (3-6 months), and slow (>6 months) cohorts based on their titration speed.

RESULTS

The statistical model revealed a significant relationship between titration speed and onset of clinical response, defined as a 50% reduction from baseline in seizure frequency. Frequency of adverse events reported between each cohort trended toward higher rates of adverse events in adults who were titrated quickly; however, the pediatric population appeared to be more tolerant of titration at any speed.

CONCLUSIONS

This analysis indicates that faster titration yields faster onset of clinical benefit and is especially practical in the pediatric population, though attempts to accelerate adult titration may still be warranted.

Neurostimulation as a Method of Treatment and a Preventive Measure in Canine Drug-Resistant Epilepsy: Current State and Future Prospects

Modulation of neuronal activity for seizure control using various methods of neurostimulation is a rapidly developing field in epileptology, especially in treatment of refractory epilepsy. Promising results in human clinical practice, such as diminished seizure burden, reduced incidence of sudden unexplained death in epilepsy, and improved quality of life has brought neurostimulation into the focus of veterinary medicine as a therapeutic option. This article provides a comprehensive review of available neurostimulation methods for seizure management in drug-resistant epilepsy in canine patients. Recent progress in non-invasive modalities, such as repetitive transcranial magnetic stimulation and transcutaneous vagus nerve stimulation is highlighted. We further discuss potential future advances and their plausible application as means for preventing epileptogenesis in dogs.

Transauricular Vagal Nerve Stimulation at 40 Hz Inhibits Hippocampal P2X7R/NLRP3/Caspase-1 Signaling and Improves Spatial Learning and Memory in 6-Month-Old APP/PS1 Mice

OBJECTIVES

Transauricular vagal nerve stimulation (taVNS) at 40 Hz attenuates hippocampal amyloid load in 6-month-old amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice, but it is unclear whether 40-Hz taVNS can improve cognition in these mice. Moreover, the underlying mechanisms are still unclear.

MATERIALS AND METHODS

6-month-old C57BL/6 (wild type [WT]) and APP/PS1 mice were subjected to 40-Hz taVNS. Novel Object Recognition and the Morris Water Maze were used to evaluate cognition. Hippocampal amyloid-β (Aβ)1-40, Aβ1-42, pro-interleukin (IL)-1β, and pro-IL-18 were measured using enzyme-linked immunosorbent assays. Hippocampal Aβ42, purinergic 2X7 receptor (P2X7R), nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3), Caspase-1, IL-1β, and IL-18 expression were evaluated by western blotting. Histologic assessments including immunofluorescence, immunohistochemistry, Nissl staining, and Congo red staining were used to assess microglial phagocytosis, neuroprotective effects, and Aβ plaque load.

RESULTS

40-Hz taVNS improved spatial memory and learning in 6-month-old APP/PS1 mice but did not affect recognition memory. There were no effects on the cognitive behaviors of 6-month-old WT mice. taVNS at 40 Hz modulated microglia; significantly decreased levels of Aβ1-40, Aβ1-42, pro-IL-1β, and pro-IL-18; inhibited Aβ42, P2X7R, NLRP3, Caspase-1, IL-1β, and IL-18 expression; reduced Aβ deposits; and had neuroprotective effects in the hippocampus of 6-month-old APP/PS1 mice. These changes were not observed in 6-month-old WT mice.

CONCLUSION

Our results show that 40-Hz taVNS inhibits the hippocampal P2X7R/NLRP3/Caspase-1 signaling and improves spatial learning and memory in 6-month-old APP/PS1 mice.

Vagus nerve stimulation for conservative therapy-refractive epilepsy and depression

Numerous studies confirm that the vagus nerve stimulation (VNS) is an efficient, indirect neuromodulatory therapy with electrically induced current for epilepsy that cannot be treated by epilepsy surgery and is therapy-refractory and for drug therapy-refractory depression. VNS is an established, evidence-based and in the long-term cost-effective therapy in an interdisciplinary overall concept.Long-term data on the safety and tolerance of the method are available despite the heterogeneity of the patient populations. Stimulation-related side effects like hoarseness, paresthesia, cough or dyspnea depend on the stimulation strength and often decrease with continuing therapy duration in the following years. Stimulation-related side effects of VNS can be well influenced by modifying the stimulation parameters. Overall, the invasive vagus nerve stimulation may be considered as a safe and well-tolerated therapy option.For invasive and transcutaneous vagus nerve stimulation, antiepileptic and antidepressant as well as positive cognitive effects could be proven. In contrast to drugs, VNS has no negative effect on cognition. In many cases, an improvement of the quality of life is possible.iVNS therapy has a low probability of complete seizure-freedom in cases of focal and genetically generalized epilepsy. It must be considered as palliative therapy, which means that it does not lead to healing and requires the continuation of specific medication. The functional principle is a general reduction of the neuronal excitability. This effect is achieved by a slow increase of the effectiveness sometimes over several years. Responders are those patients who experience a 50% reduction of the seizure incidence. Some studies even reveal seizure-freedom in 20% of the cases. Currently, it is not possible to differentiate between potential responders and non-responders before therapy/implantation.The current technical developments of the iVNS generators of the new generation like closed-loop system (cardiac-based seizure detection, CBSD) reduce also the risk for SUDEP (sudden unexpected death in epilepsy patients), a very rare, lethal complication of epilepsies, beside the seizure severity.iVNS may deteriorate an existing sleep apnea syndrome and therefore requires possible therapy interruption during nighttime (day-night programming or magnet use) beside the close cooperation with sleep physicians.The evaluation of the numerous iVNS trials of the past two decades showed multiple positive effects on other immunological, cardiological, and gastroenterological diseases so that additional therapy indications may be expected depending on future study results. Currently, the vagus nerve stimulation is in the focus of research in the disciplines of psychology, immunology, cardiology as well as pain and plasticity research with the desired potential of future medical application.Beside invasive vagus nerve stimulation with implantation of an IPG and an electrode, also devices for transdermal and thus non-invasive vagus nerve stimulation have been developed during the last years. According to the data that are currently available, they are less effective with regard to the reduction of the seizure severity and duration in cases of therapy-refractory epilepsy and slightly less effective regarding the improvement of depression symptoms. In this context, studies are missing that confirm high evidence of effectiveness. The same is true for the other indications that have been mentioned like tinnitus, cephalgia, gastrointestinal complaints etc. Another disadvantage of transcutaneous vagus nerve stimulation is that the stimulators have to be applied actively by the patients and are not permanently active, in contrast to implanted iVNS therapy systems. So they are only intermittently active; furthermore, the therapy adherence is uncertain.

Transcutaneous auricular vagal nerve stimulation inhibits limbic-regional P2X7R expression and reverses depressive-like behaviors in Zucker diabetic fatty rats

Zucker diabetic fatty (ZDF) rats develop type 2 diabetes (T2D) along with depressive-like behaviors. Transcutaneous auricular vagal nerve stimulation (taVNS) has antidiabetic and antidepressant-like effects in ZDF rats; however, the underlying antidepressant-like mechanisms are unclear. The purinergic receptor P2X7R, which is related to inflammation and depression, is upregulated in the limbic brain regions of depressed patients and rodents and is considered as a potential therapeutic target. Thus, this study aimed to provide preliminary evidence at the molecular level of taVNS antidepressant-like effect in ZDF rats through testing their limbic-regional P2X7R expression. ZDF rats were subjected to taVNS and transcutaneous non-vagal nerve stimulation (tnVNS). Body weight and blood glucose levels were monitored weekly. Depressive-like behaviors were evaluated with the open-field test (OFT) and forced swimming test (FST). Limbic-regional P2X7R expression was examined by western blotting (WB). P2X7R expressing cells were detected by immunohistochemistry (IHC). Compared to their lean littermates (ZL rats), ZDF rats developed obesity, hyperglycemia, and depressive-like behaviors with elevated limbic-regional P2X7R expression. taVNS but not tnVNS lowered body weight, reduced and stabilized blood glucose levels, suppressed limbic-regional P2X7R expression, and reversed the depressive-like behaviors. P2X7R was found primarily expressed in ZDF rats' limbic-regional astrocytes. In conclusion, taVNS inhibits ZDF rats' limbic-regional P2X7R expression, which may be one of the taVNS antidepressant-like mechanisms.

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.

Non-Invasive Transcutaneous Vagus Nerve Stimulation for the Treatment of Fibromyalgia Symptoms: A Study Protocol

Stimulation of the vagus nerve, a parasympathetic nerve that controls the neuro-digestive, vascular, and immune systems, induces pain relief, particularly in clinical conditions such as headache and rheumatoid arthritis. Transmission through vagal afferents towards the nucleus of the solitary tract (NST), the central relay nucleus of the vagus nerve, has been proposed as the main physiological mechanism that reduces pain intensity after vagal stimulation. Chronic pain symptoms of fibromyalgia patients might benefit from stimulation of the vagus nerve via normalization of altered autonomic and immune systems causing their respective symptoms. However, multi-session non-invasive vagal stimulation effects on fibromyalgia have not been evaluated in randomized clinical trials. We propose a parallel group, sham-controlled, randomized study to modulate the sympathetic–vagal balance and pain intensity in fibromyalgia patients by application of non-invasive transcutaneous vagus nerve stimulation (tVNS) over the vagal auricular and cervical branches. We will recruit 136 fibromyalgia patients with chronic moderate to high pain intensity. The primary outcome measure will be pain intensity, and secondary measures will be fatigue, health-related quality of life, sleep disorders, and depression. Heart rate variability and pro-inflammatory cytokine levels will be obtained as secondary physiological measures. We hypothesize that multiple tVNS sessions (five per week, for 4 weeks) will reduce pain intensity and improve quality of life as a result of normalization of the vagal control of nociception and immune–autonomic functions. Since both vagal branches project to the NST, we do not predict significantly different results between the two stimulation protocols.

Closed-Loop Transcutaneous Auricular Vagal Nerve Stimulation: Current Situation and Future Possibilities

Closed-loop (CL) transcutaneous auricular vagal nerve stimulation (taVNS) was officially proposed in 2020. This work firstly reviewed two existing CL-taVNS forms: motor-activated auricular vagus nerve stimulation (MAAVNS) and respiratory-gated auricular vagal afferent nerve stimulation (RAVANS), and then proposed three future CL-taVNS systems: electroencephalography (EEG)-gated CL-taVNS, electrocardiography (ECG)-gated CL-taVNS, and subcutaneous humoral signals (SHS)-gated CL-taVNS. We also highlighted the mechanisms, targets, technical issues, and patterns of CL-taVNS. By reviewing, proposing, and highlighting, this work might draw a preliminary blueprint for the development of CL-taVNS.

The Future Is Noninvasive: A Brief Review of the Evolution and Clinical Utility of Vagus Nerve Stimulation

Vagus nerve stimulation (VNS) is a form of neuromodulation that stimulates the vagus nerve. VNS had been suggested as an intervention in the late 1800s and was rediscovered in the late 1980s as a promising treatment for refractory epilepsy. Since then, VNS has been approved by the U.S. Food and Drug Administration (FDA) for treatment of epilepsy, morbid obesity, and treatment-resistant depression. Unfortunately, VNS is underutilized, as it is costly to implant and often only suggested when all other treatment options have been exhausted. Discovery of a noninvasive method of VNS known as transcutaneous auricular VNS (taVNS), which activates the vagus through stimulation of the auricular branch of the vagus nerve, has reignited excitement around VNS. taVNS has immense potential as a safe, at-home, wearable treatment for various neuropsychiatric disorders. Major strides are being made in both invasive and noninvasive VNS that aim to make this technology more accessible to patients who would find benefit, including the ongoing RECOVER trial, a randomized controlled trial in up to 1,000 individuals to further evaluate the efficacy of VNS for treatment-resistant depression. In this brief review, we first discuss the early history of VNS; then its clinical utility in FDA-approved indications; and, finally, noninvasive VNS.

Therapeutic applications of transcutaneous auricular vagus nerve stimulation with potential for application in neurodevelopmental or other pediatric disorders

Non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) as a newly developed technique involves stimulating the cutaneous receptive field formed by the auricular branch of the vagus nerve in the outer ear, with resulting activation of vagal connections to central and peripheral nervous systems. Increasing evidence indicates that maladaptive neural plasticity may underlie the pathology of several pediatric neurodevelopmental and psychiatric disorders, such as autism spectrum disorder, attention deficit hyperactivity disorder, disruptive behavioral disorder and stress-related disorder. Vagal stimulation may therefore provide a useful intervention for treating maladaptive neural plasticity. In the current review we summarize the current literature primarily on therapeutic use in adults and discuss the prospects of applying taVNS as a therapeutic intervention in specific pediatric neurodevelopmental and other psychiatric disorders. Furthermore, we also briefly discuss factors that would help optimize taVNS protocols in future clinical applications. We conclude from these initial findings that taVNS may be a promising alternative treatment for pediatric disorders which do not respond to other interventions.

The LC-NE system as a potential target for neuromodulation to ameliorate non-motor symptoms in Parkinson's disease

Parkinson's disease (PD) is associated with severe motor symptoms but also with several non-motor symptoms (NMS). A substantial reduction of norepinephrine (NE) levels in various brain regions reflecting an extensive loss of innervation from the LC has been assumed as causal for the development of NMS and specifically of attentional impairments in PD. Transcutaneous auricular vagus nerve stimulation (taVNS) is a new, non-invasive neurostimulation method supposed to modulate the LC-NE system in humans. In the current opinion paper, we introduce taVNS as a systemic approach to directly affect NE neurotransmission in healthy as well as clinical populations and discuss its potential as therapeutic option for the treatment of NMS, specifically attentional deficits, in patients with PD. Here, we first describe the LC-NE system and discuss how LC-NE dysfunction might affects cognition in PD before detailing the mode of action of taVNS and proposing its use to modulate cognitive deficits in these patients.

Use of Transcutaneous Auricular Vagus Nerve Stimulation as an Adjuvant Therapy for the Depressive Symptoms of COVID-19: A Literature Review

The coronavirus disease 2019 (COVID-19) comprises more than just severe acute respiratory syndrome. It also interacts with the cardiovascular, nervous, renal, and immune systems at multiple levels, increasing morbidity in patients with underlying cardiometabolic conditions and inducing myocardial injury or dysfunction. Transcutaneous auricular vagus nerve stimulation (taVNS), which is derived from auricular acupuncture, has become a popular therapy that is increasingly accessible to the general public in modern China. Here, we begin by outlining the historical background of taVNS, and then describe important links between dysfunction in proinflammatory cytokine release and related multiorgan damage in COVID-19. Furthermore, we emphasize the important relationships between proinflammatory cytokines and depressive symptoms. Finally, we discuss how taVNS improves immune function via the cholinergic anti-inflammatory pathway and modulates brain circuits via the hypothalamic-pituitary-adrenal axis, making taVNS an important treatment for depressive symptoms on post-COVID-19 sequelae. Our review suggests that the link between anti-inflammatory processes and brain circuits could be a potential target for treating COVID-19-related multiorgan damage, as well as depressive symptoms using taVNS.