The effect of vagus nerve stimulation on migraines

Mechanism and Applications of Vagus Nerve Stimulation

Over the past three decades, vagus nerve stimulation (VNS) has emerged as a promising rehabilitation therapy for a diverse range of conditions, demonstrating substantial clinical potential. This review summarizes the in vivo biological mechanisms activated by VNS and their corresponding clinical applications. Furthermore, it outlines the selection of parameters and equipment for VNS implementation. VNS exhibits anti-inflammatory effects, modulates neurotransmitter release, enhances neural plasticity, inhibits apoptosis and autophagy, maintains blood-brain barrier integrity, and promotes angiogenesis. Clinically, VNS has been utilized in the treatment of epilepsy, depression, headache, stroke, and obesity. Its potential applications extend to anti-inflammatory treatment and the management of cardiovascular and cerebrovascular diseases and various brain disorders. However, further experiments are required to definitively establish the efficacy of VNS's various mechanisms. Additionally, there is a need to explore and identify optimal rehabilitation treatment parameters for different diseases.

Vagus nerve stimulation: a physical therapy with promising potential for central nervous system disorders

The diseases of the central nervous system (CNS) often cause irreversible damage to the human body and have a poor prognosis, posing a significant threat to human health. They have brought enormous burdens to society and healthcare systems. However, due to the complexity of their causes and mechanisms, effective treatment methods are still lacking. Vagus nerve stimulation (VNS), as a physical therapy, has been utilized in the treatment of various diseases. VNS has shown promising outcomes in some CNS diseases and has been approved by the Food and Drug Administration (FDA) in the United States for epilepsy and depression. Moreover, it has demonstrated significant potential in the treatment of stroke, consciousness disorders, and Alzheimer's disease. Nevertheless, the exact efficacy of VNS, its beneficiaries, and its mechanisms of action remain unclear. This article discusses the current clinical evidence supporting the efficacy of VNS in CNS diseases, providing updates on the progress, potential, and potential mechanisms of action of VNS in producing effects on CNS diseases.

Association of reductions in rescue medication requirements with vagus nerve stimulation: Results of long-term community collected data from a seizure diary app

OBJECTIVE

To assess the impact of vagus nerve stimulation (VNS) on quality of life contributors such as rescue medications.

METHODS

Using the seizure diary application SeizureTracker™ database, we examined trends in rescue administration frequency before and after the first recorded VNS magnet swipe in patients with drug-resistant epilepsy who had 1) At least one VNS magnet swipe recorded in the diary, and 2) Recorded usage of a benzodiazepine rescue medication (RM) within 90 days prior to the first swipe. A paired Wilcoxon rank-sum test was used to assess changes in RM usage frequency between 30-, 60-, 90-, 180- and 360-day intervals beginning 30 days after first magnet swipe. Longitudinal changes in RM usage frequency were assessed with a generalized estimating equation model.

RESULTS

We analyzed data of 95 patients who met the inclusion criteria. Median baseline seizure frequency was 8.3 seizures per month, with median baseline rescue medication usage frequency of 2.1 administrations per month (SD 3.3). Significant reductions in rescue medication usage were observed in the 91 to 180 day interval after first VNS magnet swipe, and at 181 to 360 days and at 361 to 720 days, with the magnitude of reduction increasing over time. Decreases in rescue medication usage were sustained when controlling for patients who did not record rescue medication use after the first VNS magnet swipe (N=91). Significant predictors of reductions in rescue medication included baseline frequency of rescue medication usage and time after first VNS magnet swipe.

SIGNIFICANCE

This retrospective analysis suggests that usage of rescue medications is reduced following the start of VNS treatment in patients with epilepsy, and that the magnitude of reduction may progressively increase over time.

Anatomo-physiological basis and applied techniques of electrical neuromodulation in chronic pain

Chronic pain, a complex and debilitating condition, poses a significant challenge to both patients and healthcare providers worldwide. Conventional pharmacological interventions often prove inadequate in delivering satisfactory relief while carrying the risks of addiction and adverse reactions. In recent years, electric neuromodulation emerged as a promising alternative in chronic pain management. This method entails the precise administration of electrical stimulation to specific nerves or regions within the central nervous system to regulate pain signals. Through mechanisms that include the alteration of neural activity and the release of endogenous pain-relieving substances, electric neuromodulation can effectively alleviate pain and improve patients' quality of life. Several modalities of electric neuromodulation, with a different grade of invasiveness, provide tailored strategies to tackle various forms and origins of chronic pain. Through an exploration of the anatomical and physiological pathways of chronic pain, encompassing neurotransmitter involvement, this narrative review offers insights into electrical therapies' mechanisms of action, clinical utility, and future perspectives in chronic pain management.

Neuromodulation for Craniofacial Pain and Headaches

Headaches and facial pain are highly prevalent diseases but are often difficult to treat. Though there have been significant advances in medical management, many continue to suffer from refractory pain. Neuromodulation has been gaining interest for its therapeutic purposes in many chronic pain conditions, including headaches and facial pain. There are many potential targets of neuromodulation for headache and facial pain, and some have more robust evidence in favor of their use than others. Despite the need for more high-quality research, the available evidence for the use of neuromodulation in treating headaches and facial pain is promising. Considering the suffering that afflicts patients with intractable headache, neuromodulation may be an appropriate tool to improve not only pain but also disability and quality of life.

Role of Vagus Nerve Stimulation in the Treatment of Chronic Pain

Vagus nerve stimulation (VNS) can modulate vagal activity and neuro-immune communication. Human and animal studies have provided growing evidence that VNS can produce analgesic effects in addition to alleviating refractory epilepsy and depression. The vagus nerve (VN) projects to many brain regions related to pain processing, which can be affected by VNS. In addition to neural regulation, the anti-inflammatory property of VNS may also contribute to its pain-inhibitory effects. To date, both invasive and noninvasive VNS devices have been developed, with noninvasive devices including transcutaneous stimulation of auricular VN or carotid VN that are undergoing many clinical trials for chronic pain treatment. This review aimed to provide an update on both preclinical and clinical studies of VNS in the management for chronic pain, including fibromyalgia, abdominal pain, and headaches. We further discuss potential underlying mechanisms for VNS to inhibit chronic pain.

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.

Devices for Episodic Migraine: Past, Present, and Future

PURPOSE OF REVIEW

Historically, therapies for migraine have generally involved pharmacological treatments using non-selective or selective analgesics and preventive treatments. However, for many patients these treatments are not effective, while others prefer to use non-pharmacological-based therapies. To fill this need, over the last 15 years, neuromodulatory devices have entered the market for migraine treatment. Here, we will review the most recent findings for the use of these devices in the treatment of migraine.

RECENT FINDINGS

Non-invasive vagus nerve stimulation and spring-pulse transcranial magnetic stimulation are both cleared for the treatment of migraine, supported by preclinical studies that validate efficacy and mechanism of action, and complemented with clinical trial data. Other options also authorized for use include transcutaneous supraorbital nerve stimulation and remote electrical neuromodulation. Various options are available to treat migraine using authorized neuromodulatory devices. These data support their efficacy in the treatment of episodic migraine, although further studies are necessary to elucidate their mechanism of action and to provide rigor to clinical trial data.

Increased Concentrations of Circulating Interleukins following Non-Invasive Vagus Nerve Stimulation: Results from a Randomized, Sham-Controlled, Crossover Study in Healthy Subjects

OBJECTIVE

The vagus nerve constitutes the main component of the parasympathetic nervous system and plays an important role in the regulation of neuro-immune responses. Invasive stimulation of the vagus nerve produces anti-inflammatory effects; however, data on humoral immune responses of transcutaneous vagus nerve stimulation (tVNS) are rare. Therefore, the present study investigated changes in serum cytokine concentrations of interleukin-1β (IL-1β), IL-6, IL-8, and tumor necrosis factor α (TNFα) following a short-term, non-invasive stimulation of the vagus nerve.

METHODS

Whole blood samples were collected before and after a short-lived application of active tVNS at the inner tragus as well as sham stimulation of the earlobe. Cytokine serum concentrations were determined in two healthy cohorts of younger (n = 20) and older participants (n = 19). Differences between active and sham conditions were analyzed using linear mixed models and post hoc F tests after applying Yeo-Johnson power transformations. This trial was part of a larger study registered on ClinicalTrials.gov (NCT05007743).

RESULTS

In the young cohort, IL-6 and IL-1β concentrations were significantly increased after active stimulation, whereas they were slightly decreased after sham stimulation (IL-6: p = 0.012; IL-1β: p = 0.012). Likewise, in the older cohort, IL-1β and IL-8 concentrations were significantly elevated after active stimulation and reduced after sham application (IL-8: p = 0.007; IL-1β: p = 0.001). In contrast, circulating TNFα concentrations did not change significantly in either group.

CONCLUSION

Our results show that active tVNS led to an immediate increase in the serum concentrations of certain pro-inflammatory cytokines such as IL-1β, IL-6, and/or IL-8 in two independent cohorts of healthy study participants.

Vagal Nerve Stimulation: The Effect on the Brain Oscillatory Field Potential

More than thirty years of medical treatment with the use of vagal nerve stimulation (VNS) has shown that this therapeutic procedure works in a number of homeostatic disturbances. Although the clinical usage of VNS has a long history, our knowledge about the central mechanisms underlying this treatment is still limited. In the present paper we review the effects of VNS on brain oscillations as a possible electrophysiological bio-marker of VNS efficacy. The review was prepared mainly on the basis of data delivered from clinical observations and the outcomes of electrophysiological experiments conducted on laboratory animals that are available in PubMed. We consciously did not focus on epileptiform activity understood as a pathologic oscillatory activity, which was widely discussed in the numerous previously published reviews. The main conclusion of the present paper is that further, well-designed experiments on laboratory animals are absolutely necessary to address the electrophysiological issues. These will fill a number of gaps in our present knowledge of the central mechanisms underlying VNS therapy.

Vagus nerve afferent stimulation: Projection into the brain, reflexive physiological, perceptual, and behavioral responses, and clinical relevance

The afferent vagus nerves project to diverse neural networks within the brainstem and forebrain, based on neuroanatomical, neurophysiological, and functional (fMRI) brain imaging evidence. In response to afferent vagal stimulation, multiple homeostatic visceral reflexes are elicited. Physiological stimuli and both invasive and non-invasive electrical stimulation that activate the afferent vagus elicit perceptual and behavioral responses that are of physiological and clinical significance. In the present review, we address these multiple roles of the afferent vagus under normal and pathological conditions, based on both animal and human evidence.

Peripheral Nerve Stimulation for Treatment of Headaches: An Evidence-Based Review

Headaches are one of the most common medical complaints worldwide, and treatment is often made difficult because of misclassification. Peripheral nerve stimulation has emerged as a novel treatment for the treatment of intractable headaches in recent years. While high-quality evidence does exist regarding its use, efficacy is generally limited to specific nerves and headache types. While much research remains to bring this technology to the mainstream, clinicians are increasingly able to provide safe yet efficacious pain control.

tVNS in the management of headache and pain

First clinical observations of the therapeutic effect of vagus nerve stimulation were of patients who were treated for refractory epilepsy with a fully implanted vagus nerve stimulator, who also reported an improvement of their migraine and cluster headache. With the development of non-invasive vagus nerve stimulation, first clinical studies concerning a possible therapeutic effect in migraine and cluster headache were performed. In a controlled study, transcutaneous cervical vagus nerve stimulation (tcVNS) showed a significant but limited effect in acute treatment of a migraine attack. There was no significant prophylactic effect in episodic migraine. Concerning cluster headache, there was a clear beneficial effect in the prophylaxis of chronic cluster headache and in the attack treatment in episodic cluster headache. There are fewer studies in the literature on the effect of transcutaneous auricular vagus nerve stimulation (taVNS), with a partial overlap with studies on electrical ear acupuncture. In a small controlled clinical trial, there was a significant effect of taVNS in the prevention of chronic migraine. In less defined clinical studies, there were some positive signs that the method may be beneficial in chronic back pain and in unspecific gastro-intestinal pain in adolescents. Based on the available evidence, it is probable that vagus nerve stimulation can have a clinically meaningful influence on pain syndromes, but there are still several questions (e.g. frequency of the stimulation; duration of the stimulation; differential effects of auricular vagus stimulation and cervical vagus stimulation) to answer before vagus stimulation can be used widely in the clinic.

Vagus Nerve Stimulation Ameliorates Cognitive Impairment and Increased Hippocampal Astrocytes in a Mouse Model of Gulf War Illness

Gulf war illness (GWI), is a chronic multi-symptom illness that has impacted approximately one-third of the veterans who served in the 1990 to 1991 Gulf War. GWI symptoms include cognitive impairments (eg, memory and concentration problems), headaches, migraines, fatigue, gastrointestinal and respiratory issues, as well as emotional deficits. The exposure to neurological chemicals such as the anti-nerve gas drug, pyridostigmine bromide (PB), and the insecticide permethrin (PER), may contribute to the etiologically related factors of GWI. Various studies utilizing mouse models of GWI have reported the interplay of these chemical agents in increasing neuroinflammation and cognitive dysfunction. Astrocytes are involved in the secretion of neuroinflammatory cytokines and chemokines in pathological conditions and have been implicated in GWI symptomology. We hypothesized that exposure to PB and PER causes lasting changes to hippocampal astrocytes, concurrent with chronic cognitive deficits that can be reversed by cervical vagus nerve stimulation (VNS). GWI was induced in CD1 mice by injecting the mixture of PER (200 mg/kg) and PB (2 mg/kg), i.p. for 10 consecutive days. VNS stimulators were implanted at 33 weeks after GWI induction. The results show age-related cognitive alterations at approximately 9 months after exposure to PB and PER. The results also showed an increased number of GFAP-labeled astrocytes in the hippocampus and dentate gyrus that was ameliorated by VNS.

Vagus nerve stimulation in brain diseases: Therapeutic applications and biological mechanisms

Brain diseases, including neurodegenerative, cerebrovascular and neuropsychiatric diseases, have posed a deleterious threat to human health and brought a great burden to society and the healthcare system. With the development of medical technology, vagus nerve stimulation (VNS) has been approved by the Food and Drug Administration (FDA) as an alternative treatment for refractory epilepsy, refractory depression, cluster headaches, and migraines. Furthermore, current evidence showed promising results towards the treatment of more brain diseases, such as Parkinson's disease (PD), autistic spectrum disorder (ASD), traumatic brain injury (TBI), and stroke. Nonetheless, the biological mechanisms underlying the beneficial effects of VNS in brain diseases remain only partially elucidated. This review aims to delve into the relevant preclinical and clinical studies and update the progress of VNS applications and its potential mechanisms underlying the biological effects in brain diseases.

Heart Rate Variability Analysis in Episodic Migraine: A Cross-Sectional Study

Objective: It has been reported that autonomic nervous dysfunction is more prevalent in migraineurs. Heart rate variability (HRV) is a commonly used method to evaluate the cardiac autonomic nervous function modulation. However, HRV changes in migraine are still contradictory. The main objective of this study was to explore the potential HRV change patterns in episodic migraine (EM) and whether there were differences in HRV between EM ictal period and the interictal period.

Patients and Methods: We conducted a cross-sectional study including 18 patients with EM and 18 age- and sex-matched controls. The characteristics of demographics, some lifestyle factors, and psychological conditions were assessed at baseline. HRVs including time-domain analysis and frequency-domain analysis were performed in all participants. HRV analyses in migraine were recorded not only in the interictal period but also in the ictal period.

Results: All the HRV parameters showed a decreased trend in migraine than controls. Time-domain parameters standard deviation of all NN intervals in 24 h (SDNN) and triangular index were significantly lower in the migraine ictal period than controls separately (SDNN, 56.94 ± 22.09 ± 7.76 vs. 135.78 ± 35.16, p < 0.001; triangular index, 12.61 ± 3.20 vs. 22.11 ± 6.90, p < 0.001). Frequency-domain parameter low-frequency power was also lower in the migraine ictal period than controls (351.28 ± 206.71 vs. 559.61 ± 281.24, p = 0.02). SDNN was much lower in the migraine ictal period than migraine interictal period (56.94 ± 22.09 vs. 115.94 ± 46.88, p < 0.001). HRV changes during migraine interictal period did not differ from the control group. The correlation analysis revealed a negative correlation between visual analog scale and HRV parameters in the migraine ictal period (p = 0.04).

Conclusions: The present cross-sectional study indicates that HRV was significantly decreased in EM population especially during the migraine ictal period, which means unbalance of autonomic system in EM. Perhaps larger prospective cohort studies are wanted to validate these findings.

Update on noninvasive neuromodulation for migraine treatment-Vagus nerve stimulation

Noninvasive neurostimulation methods are particularly suited for migraine treatment thanks to their most favorable adverse event profile. Among them, noninvasive vagus nerve stimulation (nVNS) has raised great hope because of the role the vagus nerve is known to play in pain modulation, inflammation and brain excitability. We will critically review the clinical studies performed for migraine attack treatment and migraine prevention with the GammaCore® device, which allows cervical vagus nerve stimulation. nVNS is effective for the abortive treatment of migraine attacks, although the effect size is modest and numbers-to-treat appear not superior to those of other noninvasive neurostimulation methods, and inferior to those of oral triptans. The effect of nVNS with the GammaCore® in migraine prevention is not superior to sham stimulation, except possibly in patients with high adherence to the treatment. Both in acute and preventive trials, nVNS was characterized by an outstanding tolerance and safety profile, like the other noninvasive neurostimulation techniques. In physiological animal and human studies, cervical nVNS was shown to generate somatosensory evoked responses, to modulate pain perception and several areas of the cerebral pain network, and to inhibit experimental cortical spreading depression, which are relevant effects for migraine therapy.

Therapeutic implications of cortical spreading depression models in migraine

Migraine is among the most common and disabling neurological diseases in the world. Cortical spreading depression (CSD) is a wave of near-complete depolarization of neurons and glial cells that slowly propagates along the cortex creating the perception of aura. Evidence suggests that CSD can trigger migraine headache. Experimental models of CSD have been considered highly translational as they recapitulate migraine-related phenomena and have been validated for screening migraine therapeutics. Here we outline the essential components of validated experimental models of CSD and provide a comprehensive review of potential modulators and targets against CSD. We further focus on novel interventions that have been recently shown to suppress CSD susceptibility that may lead to therapeutic targets in migraine.

Auricular Electrical Stimulation Alleviates Headache through CGRP/COX-2/TRPV1/TRPA1 Signaling Pathways in a Nitroglycerin-Induced Migraine Rat Model

The study aimed to investigate effect of auricular electrical stimulation (ES) on migraine. Migraine was induced in rats by intraperitoneal administration of nitroglycerin (NTG, 10 mg/kg) three times. Auricular ES pretreatment was performed for five consecutive days. Migraine behaviors were observed by a video recording. Auricular ES pretreatment could reverse the decrease of the total time spent on exploratory (2619.0 ± 113.0 s vs 1581.7 ± 217.6 s, p=0.0029) and locomotor behaviors (271.3 ± 21.4 s vs 114.3 ± 19.7 s, p=0.0135) and also could reverse the increase of the total time spent on resting (19.0 ± 10.6 s vs 154.3 ± 46.5 s, p=0.0398) and grooming (369.9 ± 66.8 s vs 1302.0 ± 244.5 s, p=0.0324) behaviors. Auricular ES pretreatment could increase the frequency of rearing behaviors (38.0 ± 1.8 vs 7.7 ± 3.5, p < 0.0001) and total distance traveled (1372.0 ± 157.9 cm vs 285.3 ± 85.6 cm, p < 0.0001) and also could increase the percentage of inner zone time (6.0 ± 1.6% vs 0.4 ± 0.2%, p=0.0472). The CGRP, COX-2, TRPV1, and TRPA1 immunoreactive cells in the trigeminal ganglion increased in the NTG group compared with the control group (all p < 0.0001); this increase could, however, be reduced by auricular ES pretreatment (27.8 ± 2.6 vs 63.0 ± 4.2, p < 0.0001; 21.7 ± 1.2 vs 61.8 ± 4.0, p < 0.0001; 24.3 ± 1.0 vs 36.5 ± 1.7, p=0.0003; and 20.7 ± 1.9 vs 90.8 ± 6.5, p < 0.0001, respectively). Therefore, we suggest that auricular ES pretreatment is beneficial for the treatment of migraine and this effect is partly related to CGRP/COX-2/TRPV1/TRPA1 signaling pathways.

[Peripheral neurostimulation in headache treatment]

According to rough estimates, at least one third of the population in developed countries suffers, to varying degrees, from certain forms of primary headache, the modern pharmacotherapy of which is not always effective and has a number of limitations. The non-pharmacological treatment of headache can be an alternative to the prescription of pharmacological agents and the only possible assistance option for patients developing drug-resistant cephalalgias. This review describes various methods of electrical neuromodulation that are used for the management of primary headaches. The authors provide information on current stages in implementation of implantable and non-invasive equipment into clinical practice, which makes possible electrical stimulations of peripheral nerves and of the sphenopalatine ganglion, as well as allows transcranial magnetic stimulation. Also the appearance and usage of portable electrical devices available on the world market are described, and mechanisms that can underlie anticephalgic action of neuromodulation therapy are discussed. Special attention is paid to the methods that are applied for electrostimulation of the vagus nerve and occipital nerves.

Brainstem neuroimaging of nociception and pain circuitries

The brainstem is known to be an important brain area for nociception and pain processing, and both relaying and coordinating signaling between the cerebrum, cerebellum, and spinal cord. Although preclinical models of pain have characterized the many roles that brainstem nuclei play in nociceptive processing, the degree to which these circuitries extend to humans is not as well known. Unfortunately, the brainstem is also a very challenging region to evaluate in humans with neuroimaging. The challenges for human brainstem imaging arise from the location of this elongated brain structure, proximity to cardiorespiratory noise sources, and the size of its constituent nuclei. These challenges can require dedicated approaches to brainstem imaging, which should be adopted when study hypotheses are focused on brainstem processing of nociception or modulation of pain perception. In fact, our review will highlight many pain neuroimaging studies that have reported some brainstem involvement in nociceptive processing and chronic pain pathology. However, we note that with recent advances in neuroimaging leading to improved spatial and temporal resolution, more studies are needed that take advantage of data collection and analysis methods focused on the challenges of brainstem neuroimaging.

Treating Chronic Migraine With Neuromodulation: The Role of Neurophysiological Abnormalities and Maladaptive Plasticity

Chronic migraine (CM) is the most disabling form of migraine, because pharmacological treatments have low efficacy and cumbersome side effects. New evidence has shown that migraine is primarily a disorder of brain plasticity and migraine chronification depends on a maladaptive process favoring the development of a brain state of hyperexcitability. Due to the ability to induce plastic changes in the brain, researchers started to look at Non-Invasive Brain Stimulation (NIBS) as a possible therapeutic option in migraine field. On one side, NIBS techniques induce changes of neural plasticity that outlast the period of the stimulation (a fundamental prerequisite of a prophylactic migraine treatment, concurrently they allow targeting neurophysiological abnormalities that contribute to the transition from episodic to CM. The action may thus influence not only the cortex but also brainstem and diencephalic structures. Plus, NIBS is not burdened by serious medication side effects and drug–drug interactions. Although the majority of the studies reported somewhat beneficial effects in migraine patients, no standard intervention has been defined. This may be due to methodological differences regarding the used techniques (e.g., transcranial magnetic stimulation, transcranial direct current stimulation), the brain regions chosen as targets, and the stimulation types (e.g., the use of inhibitory and excitatory stimulations on the basis of opposite rationales), and an intrinsic variability of stimulation effect. Hence, it is difficult to draw a conclusion on the real effect of neuromodulation in migraine. In this article, we first will review the definition and mechanisms of brain plasticity, some neurophysiological hallmarks of migraine, and migraine chronification-related (dys)plasticity. Secondly, we will review available results from therapeutic and physiological studies using neuromodulation in CM. Lastly we will discuss the results obtained in these preventive trials in the light of a possible effect on brain plasticity.

Neurostimulation for the treatment of chronic migraine and cluster headache

Small subsets of patients who fail to respond to pharmacological treatment may benefit from alternative treatment methods. In the last decade, neurostimulation is being explored as a potential treatment option for the patients with chronic, severely disabling refractory primary headaches. To alleviate pain, specific nerves and brain areas have been stimulated, and various methods have been explored: deep brain stimulation, occipital nerve stimulation, and sphenopalatine ganglion stimulation are among the more invasive ones, whereas transcranial magnetic stimulation and supraorbital nerve stimulation are noninvasive. Vagal nerve stimulation can be invasive or noninvasive, though this review included only data for noninvasive VNS. Most of these methods have been tested in small open-label patient series; recently, more data from randomized, controlled, and blinded studies are available. Although neurostimulation treatments have demonstrated good efficacy in many studies, it still has not been established as a standard treatment in refractory patients. This review analyzes the available evidence regarding efficacy and safety of different neurostimulation modalities for the treatment of chronic migraine and cluster headache.

Medial septal cholinergic mediation of hippocampal theta rhythm induced by vagal nerve stimulation

BACKGROUND

Electrical vagal nerve stimulation (VNS) has been used for years to treat patients with drug-resistant epilepsy. This technique also remains under investigation as a specific treatment of patients with Alzheimer's disease. Recently we discovered that VNS induced hippocampal formation (HPC) type II theta rhythm, which is involved in memory consolidation. In the present study, we have extended our previous observation and addressed the neuronal substrate and pharmacological profile of HPC type II theta rhythm induced by VNS in anesthetized rats.

METHODS

Male Wistar rats were implanted with a VNS cuff electrode around the left vagus nerve, a tungsten microelectrode for recording the HPC field activity, and a medial septal (MS) cannula for the injection of a local anesthetic, procaine, and muscarinic agents. A direct, brief effect of VNS on the HPC field potential was evaluated before and after medial-septal drug injection.

RESULTS

Medial septal injection of local anesthetic, procaine, reversibly abolished VNS-induced HPC theta rhythm. With the use of cholinergic muscarinic agonist and antagonists, we demonstrated that medial septal M1 receptors are involved in the mediation of the VNS effect on HPC theta field potential.

CONCLUSION

The MS cholinergic M1 receptor mechanism integrates not only central inputs from the brainstem synchronizing pathway, which underlies the production of HPC type II theta rhythm, but also the input from the vagal afferents in the brain stem.

Spotlight on cervical vagus nerve stimulation for the treatment of primary headache disorders: a review

Objectives

Cervical noninvasive vagus nerve stimulation (nVNS) emerged as an adjunctive neuromodulation approach for primary headache disorders with limited responsiveness to pharmacologic and behavioral treatment. This narrative review evaluates the safety and efficacy of invasive and noninvasive peripheral nerve stimulation of the cervical branch of the vagal nerve (afferent properties) for primary headache disorders (episodic/chronic migraine [EM/CM] and cluster headache [ECH/CCH]) and provides a brief summary of the preclinical data on the possible mechanism of action of cervical vagus nerve stimulation (VNS) and trigemino-nociceptive head pain transmission.

Materials and methods

A systematic search of published data was performed in PubMed for randomized controlled trials (RCTs) and prospective cohort clinical studies assessing the efficacy/safety and cost-effectiveness of cervical VNS in primary headache disorders and related preclinical studies.

Results

Three RCTs were identified for ECH/CCH (ACT-1, ACT-2 and PREVA), one RCT for migraine (EVENT) and several prospective cohort studies and retrospective analyses for both headache disorders. In ACT-1, a significantly higher response rate, a higher pain-free rate and a decrease in mean attack duration were found in nVNS-treated ECH/CCH patients compared to sham stimulation. ACT-2 confirmed these findings (e.g., significantly higher pain-free attacks, pain severity decline and increased responder-rate [defined as ≥50% reduction]). The PREVA study demonstrated the superiority of adjunctive nVNS to standard care alone and observed a significantly higher attack reduction (p=0.02) and responder rate (defined as ≥50% reduction). For CM, the EVENT study assessed a significantly higher frequency of decline in the open-label phase. Mostly transient mild/moderate adverse events were recorded, and no severe device-related adverse events occurred.

Conclusion

Cervical nVNS represents a novel, safe and efficient adjunctive treatment option for primary headache disorders. In particular, preliminary observations suggest enhanced nVNS responsiveness in favor of episodic subtypes (EM and ECH). However, preclinical studies are urgently warranted to dissect the mechanism of action.

Autonomic responses to tooth clenching in migraineurs-augmented trigeminocardiac reflex?

BACKGROUND

Systemic autonomic changes are well known in migraineurs. Also, masticatory disorders are reported to be associated with migraine. However, if those phenomena are interrelated, and how, is unclear. Moreover, the knowledge on the autonomic responses to masticatory stimuli in migraineurs is limited.

OBJECTIVE

To investigate tooth clenching-related cardiac autonomic regulation in migraineurs.

METHODS

We compared maximal tooth clenching-induced systemic autonomic responses, indicated by heart rate variability and blood pressure changes, in headache-free migraineurs (n = 17) and control subjects (n = 22).

RESULTS

Levels of high-frequency power, reflecting vagal activity, were lower in migraineurs at baseline but increased after tooth clenching whereas in controls they returned to baseline (P < 0.05, mixed model analysis). In multivariate regression model, the presence of migraine predicted the baseline levels of low- and high-frequency power and sympathovagal balance, and the post-test increase in high-frequency power, with the attack frequency and side of headache as the modifiers of the measured changes in migraineurs. The painful signs of temporomandibular disorders, found in clinical oral examination, enhanced both maximal changes in RR intervals and post-test vagal responses to tooth clenching only in migraineurs.

CONCLUSION

The enhanced post-clenching vagal activation may represent a marker of the augmented trigeminocardiac reflex to stimulation of trigeminal area, sensitised in migraineurs. Our results support an involvement of autonomic mechanisms in migraine pathophysiology and are interesting in terms of interactions between migraine and masticatory disorders, elucidating one potential way how masticatory disorders may aggravate migraine.

Modulation of brainstem activity and connectivity by respiratory-gated auricular vagal afferent nerve stimulation in migraine patients

Migraine pathophysiology includes altered brainstem excitability, and recent neuromodulatory approaches aimed at controlling migraine episodes have targeted key brainstem relay and modulatory nuclei. In this study, we evaluated the impact of respiratory-gated auricular vagal afferent nerve stimulation (RAVANS), a novel neuromodulatory intervention based on an existing transcutaneous vagus nerve stimulation approach, in the modulation of brainstem activity and connectivity in migraine patients. We applied 3T-functional magnetic resonance imaging with improved in-plane spatial resolution (2.62 × 2.62 mm) in episodic migraine (interictal) and age- and sex-matched healthy controls to evaluate brain response to RAVANS (gated to either inhalation or exhalation) and sham stimulation. We further investigated RAVANS modulation of tactile trigeminal sensory afference response in the brainstem using air-puff stimulation directed to the forehead during functional magnetic resonance imaging. Compared with sham and inhalatory-gated RAVANS (iRAVANS), exhalatory-gated RAVANS (eRAVANS) activated an ipsilateral pontomedullary region consistent with nucleus tractus solitarii (NTS). During eRAVANS, NTS connectivity was increased to anterior insula and anterior midcingulate cortex, compared with both sham and iRAVANS, in migraine patients. Increased connectivity was inversely correlated with relative time to the next migraine attack, suggesting clinical relevance to this change in connectivity. Poststimulation effects were also noted immediately after eRAVANS, as we found increased activation in putative pontine serotonergic (ie, nucleus raphe centralis) and noradrenergic (ie, locus coeruleus) nuclei in response to trigeminal sensory afference. Regulation of activity and connectivity of brainstem and cortical regions involved in serotonergic and noradrenergic regulation and pain modulation may constitute an underlying mechanism supporting beneficial clinical outcomes for eRAVANS applied for episodic migraine.

Vagus nerve stimulation inhibits trigeminal nociception in a rodent model of episodic migraine

INTRODUCTION

Although neck muscle tension is considered a risk factor for migraine, pungent odors can act as a trigger to initiate an attack in sensitized individuals. Although noninvasive vagus nerve stimulation (nVNS) is now an approved treatment for chronic migraine, how it functions to inhibit trigeminal nociception in an episodic migraine model is not known.

OBJECTIVES

The objectives of this study were to determine if nVNS could inhibit trigeminal nociception in a novel model of episodic migraine and investigate changes in the expression of proteins implicated in peripheral and central sensitization.

METHODS

Sprague-Dawley male rats were injected with an inflammatory agent in the trapezius muscle before exposure to pungent volatile compounds, which was used to initiate trigeminal nociceptor activation. The vagus nerve was stimulated transdermally by a 1-ms pulse of 5 kHz sine waves, repeated at 25 Hz for 2 minutes. Nocifensive head withdrawal response to von Frey filaments was determined and immunoreactive protein levels in the spinal cord and trigeminal ganglion (TG) were investigated.

RESULTS

Exposure to the pungent odor significantly increased the number of nocifensive withdrawals in response to mechanical stimulation of sensitized TG neurons mediated by neck muscle inflammation. Noninvasive vagus nerve stimulation inhibited nociception and repressed elevated levels of P-ERK in TG, Iba1 in microglia, and GFAP in astrocytes from sensitized animals exposed to the pungent odor.

CONCLUSION

Our findings demonstrate that nVNS inhibits mechanical nociception and represses expression of proteins associated with peripheral and central sensitization of trigeminal neurons in a novel rodent model of episodic migraine.

Chronic interfacing with the autonomic nervous system using carbon nanotube (CNT) yarn electrodes

The ability to reliably and safely communicate chronically with small diameter (100–300 µm) autonomic nerves could have a significant impact in fundamental biomedical research and clinical applications. However, this ability has remained elusive with existing neural interface technologies. Here we show a new chronic nerve interface using highly flexible materials with axon-like dimensions. The interface was implemented with carbon nanotube (CNT) yarn electrodes to chronically record neural activity from two separate autonomic nerves: the glossopharyngeal and vagus nerves. The recorded neural signals maintain a high signal-to-noise ratio (>10 dB) in chronic implant models. We further demonstrate the ability to process the neural activity to detect hypoxic and gastric extension events from the glossopharyngeal and vagus nerves, respectively. These results establish a novel, chronic platform neural interfacing technique with the autonomic nervous system and demonstrate the possibility of regulating internal organ function, leading to new bioelectronic therapies and patient health monitoring.

Novel Therapeutic Targets Against Spreading Depression

Migraine is among the most prevalent and disabling neurological diseases in the world. Cortical spreading depression (SD) is an intense wave of neuronal and glial depolarization underlying migraine aura, and a headache trigger, which has been used as an experimental platform for drug screening in migraine. Here, we provide an overview of novel therapeutic targets that show promise to suppress SD, such as acid-sensing ion channels, casein kinase Iδ, P2X7-pannexin 1 complex, and neuromodulation, and outline the experimental models and essential quality measures for rigorous and reproducible efficacy testing.

Do the psychological effects of vagus nerve stimulation partially mediate vagal pain modulation?

There is preclinical and clinical evidence that vagus nerve stimulation modulates both pain and mood state. Mechanistic studies show brainstem circuitry involved in pain modulation by vagus nerve stimulation, but little is known about possible indirect descending effects of altered mood state on pain perception. This possibility is important, since previous studies have shown that mood state affects pain, particularly the affective dimension (pain unpleasantness). To date, human studies investigating the effects of vagus nerve stimulation on pain perception have not reliably measured psychological factors to determine their role in altered pain perception elicited by vagus nerve stimulation. Thus, it remains unclear how much of a role psychological factors play in vagal pain modulation. Here, we present a rationale for including psychological measures in future vagus nerve stimulation studies on pain.

Challenges and opportunities for brainstem neuroimaging with ultrahigh field MRI

The human brainstem plays a central role in connecting the cerebrum, the cerebellum and the spinal cord to one another, hosting relay nuclei for afferent and efferent signaling, and providing source nuclei for several neuromodulatory systems that impact central nervous system function. While the investigation of the brainstem with functional or structural magnetic resonance imaging has been hampered for years due to this brain structure's physiological and anatomical characteristics, the field has seen significant advances in recent years thanks to the broader adoption of ultrahigh-field (UHF) MRI scanning. In the present review, we focus on the advantages offered by UHF in the context of brainstem imaging, as well as the challenges posed by the investigation of this complex brain structure in terms of data acquisition and analysis. We also illustrate how UHF MRI can shed new light on the neuroanatomy and neurophysiology underlying different brainstem-based circuitries, such as the central autonomic network and neurotransmitter/neuromodulator systems, discuss existing and foreseeable clinical applications to better understand diseases such as chronic pain and Parkinson's disease, and explore promising future directions for further improvements in brainstem imaging using UHF MRI techniques.

Invasive and Non-invasive Electrical Pericranial Nerve Stimulation for the Treatment of Chronic Primary Headaches

Chronic primary headaches are widespread disorders which cause significant quality of life and socioprofessional impairment. Available pharmacological treatments have often a limited efficacy and/or can generate unbearable side effects. Electrical nerve stimulation is a well-known non-destructive method of pain modulation which has been recently applied to headache management. In this review, we summarise recent advances in invasive and non-invasive neurostimulation techniques targeting pericranial structures for the treatment of chronic primary headaches, chiefly migraine and cluster headache: occipital nerve, supraorbital nerve, vagus nerve, and sphenopalatine ganglion stimulations. Invasive neurostimulation therapies have offered a new hope to drug-refractory headache sufferers but are not riskless and should be proposed only to chronic patients who failed to respond to most existing preventives. Non-invasive neurostimulation devices are user-friendly, safe and well tolerated and are thus taking an increasing place in the multidisciplinary therapeutical armamentarium of primary headaches.

Current Approaches to Neuromodulation in Primary Headaches: Focus on Vagal Nerve and Sphenopalatine Ganglion Stimulation

Neuromodulation is a promising, novel approach for the treatment of primary headache disorders. Neuromodulation offers a new dimension in the treatment that is both easily reversible and tends to be very well tolerated. The autonomic nervous system is a logical target given the neurobiology of common primary headache disorders, such as migraine and the trigeminal autonomic cephalalgias (TACs). This article will review new encouraging results of studies from the most recent literature on neuromodulation as acute and preventive treatment in primary headache disorders, and cover some possible underlying mechanisms. We will especially focus on vagus nerve stimulation (VNS) and sphenopalatine ganglion (SPG) since they have targeted autonomic pathways that are cranial and can modulate relevant pathophysiological mechanisms. The initial data suggests these approaches will find an important role in headache disorder management going forward.

Vagus nerve stimulation inhibits cortical spreading depression

Vagus nerve stimulation has recently been reported to improve symptoms of migraine. Cortical spreading depression is the electrophysiological event underlying migraine aura and is a trigger for headache. We tested whether vagus nerve stimulation inhibits cortical spreading depression to explain its antimigraine effect. Unilateral vagus nerve stimulation was delivered either noninvasively through the skin or directly by electrodes placed around the nerve. Systemic physiology was monitored throughout the study. Both noninvasive transcutaneous and invasive direct vagus nerve stimulations significantly suppressed spreading depression susceptibility in the occipital cortex in rats. The electrical stimulation threshold to evoke a spreading depression was elevated by more than 2-fold, the frequency of spreading depressions during continuous topical 1 M KCl was reduced by ∼40%, and propagation speed of spreading depression was reduced by ∼15%. This effect developed within 30 minutes after vagus nerve stimulation and persisted for more than 3 hours. Noninvasive transcutaneous vagus nerve stimulation was as efficacious as direct invasive vagus nerve stimulation, and the efficacy did not differ between the ipsilateral and contralateral hemispheres. Our findings provide a potential mechanism by which vagus nerve stimulation may be efficacious in migraine and suggest that susceptibility to spreading depression is a suitable platform to optimize its efficacy.

Extended Long-Term Effects of Cervical Vagal Nerve Stimulation on Headache Intensity/Frequency and Affective/Cognitive Headache Perception in Drug Resistant Complex-Partial Seizure Patients

OBJECTIVES

Invasive vagal nerve stimulation (iVNS) is an established treatment option for drug-resistant focal seizures and has been assumed to diminish frequent co-incidental daily headache/migraine. However, long-term effects on cognitive/affective head pain perception, headache intensity/frequency are lacking. We therefore investigated potential iVNS-induced effects in patients with drug-resistant focal seizure and daily headache/migraine.

MATERIALS AND METHODS

A clinical database was used to select 325 patients with drug-resistant epilepsy treated by either iVNS plus best medical treatment (BMT) or BMT alone, compared to a healthy control group (HC). We assessed headache intensity (VAS), headache frequency, affective/cognitive pain perception (PASS; FSVA), migraine disability scores (MIDAS), sleep architecture (PSQI), depressive symptoms (BDI), and body weight (BMI).

RESULTS

Nineteen patients with daily headache/migraine composed the clinical groups (10 iVNS and 9 BMT; iVNS mean age 49 years, range 36-61 years; BMT mean age 45 years, range 23-63 years; equally distributed gender). Cervical iVNS was applied from 5-13 years (mean 8 years) with following stimulation patterns: 1.3 mA (0.5-2 mA), 20 Hz, 250 μsec, 30 sec on/1.9 min off (0.5-5 min). The iVNS group had significantly lower VAS scores (iVNS 5.4; BMT 7.8; p = 0.03) and PASS cognitive/anxiety subscores (iVNS 21; BMT 16; p = 0.02) compared to BMT and HC. Global PASS (p = 0.07), FSVA, PSQI, BDI, and BMI scores did not differ significantly between groups.

CONCLUSIONS

iVNS appears to have positive modulatory long-term effects on headache and affective/cognitive head pain perception in patients with drug-resistant focal epilepsy, thus deserving further attention.

Pathophysiological targets for non-pharmacological treatment of migraine

Background Migraine is the most prevalent neurological disorder worldwide and ranked sixth among all diseases in years lived with disability. Overall preventive anti-migraine therapies have an effect in one patient out of two at the most, many of them being endowed with disabling adverse effects. No new disease-modifying drugs have come into clinical practice since the application to migraine of topiramate and botulinum toxin, the latter for its chronic form. There is thus clearly a need for more effective treatments that are devoid of, or have acceptable side effects. In recent years, scientific progress in migraine research has led to substantial changes in our understanding of the pathophysiology of migraine and paved the way for novel non-drug pathophysiological-targeted treatment strategies. Overview Several such non-drug therapies have been tested in migraine, such as oxidative phosphorylation enhancers, diets and non-invasive central or peripheral neurostimulation. All of them are promising for preventive migraine treatment and are quasi-devoid of side effects. Their advantage is that they can in theory be selected for individual patients according to their pathophysiological profile and they can (and probably should) be combined with the classical pharmacological armamentarium. Conclusion We will review here how knowledge of the functional anatomy and physiology of migraine mechanisms holds the key for more specific and effective non-pharmacological treatments.

Chronic migraine headache prevention with noninvasive vagus nerve stimulation: The EVENT study

Objective:

To evaluate the feasibility, safety, and tolerability of noninvasive vagus nerve stimulation (nVNS) for the prevention of chronic migraine (CM) attacks.

Methods:

In this first prospective, multicenter, double-blind, sham-controlled pilot study of nVNS in CM prophylaxis, adults with CM (≥15 headache d/mo) entered the baseline phase (1 month) and were subsequently randomized to nVNS or sham treatment (2 months) before receiving open-label nVNS treatment (6 months). The primary endpoints were safety and tolerability. Efficacy endpoints in the intent-to-treat population included change in the number of headache days per 28 days and acute medication use.

Results:

Fifty-nine participants (mean age, 39.2 years; mean headache frequency, 21.5 d/mo) were enrolled. During the randomized phase, tolerability was similar for nVNS (n = 30) and sham treatment (n = 29). Most adverse events were mild/moderate and transient. Mean changes in the number of headache days were −1.4 (nVNS) and −0.2 (sham) (Δ = 1.2; p = 0.56). Twenty-seven participants completed the open-label phase. For the 15 completers initially assigned to nVNS, the mean change from baseline in headache days after 8 months of treatment was −7.9 (95% confidence interval −11.9 to −3.8; p < 0.01).

Conclusions:

Therapy with nVNS was well-tolerated with no safety issues. Persistent prophylactic use may reduce the number of headache days in CM; larger sham-controlled studies are needed.

ClinicalTrials.gov identifier:

NCT01667250.

Classification of evidence:

This study provides Class II evidence that for patients with CM, nVNS is safe, is well-tolerated, and did not significantly change the number of headache days. This pilot study lacked the precision to exclude important safety issues or benefits of nVNS.

Chronic migraine: risk factors, mechanisms and treatment

Chronic migraine has a great detrimental influence on a patient's life, with a severe impact on socioeconomic functioning and quality of life. Chronic migraine affects 1-2% of the general population, and about 8% of patients with migraine; it usually develops from episodic migraine at an annual conversion rate of about 3%. The chronification is reversible: about 26% of patients with chronic migraine go into remission within 2 years of chronification. The most important modifiable risk factors for chronic migraine include overuse of acute migraine medication, ineffective acute treatment, obesity, depression and stressful life events. Moreover, age, female sex and low educational status increase the risk of chronic migraine. The pathophysiology of migraine chronification can be understood as a threshold problem: certain predisposing factors, combined with frequent headache pain, lower the threshold of migraine attacks, thereby increasing the risk of chronic migraine. Treatment options include oral medications, nerve blockade with local anaesthetics or corticoids, and neuromodulation. Well-defined diagnostic criteria are crucial for the identification of chronic migraine. The International Headache Society classification of chronic migraine was recently updated, and now allows co-diagnosis of chronic migraine and medication overuse headache. This Review provides an up-to-date overview of the classification of chronic migraine, basic mechanisms and risk factors of migraine chronification, and the currently established treatment options.

Vagus nerve stimulation: state of the art of stimulation and recording strategies to address autonomic function neuromodulation

OBJECTIVE

Neural signals along the vagus nerve (VN) drive many somatic and autonomic functions. The clinical interest of VN stimulation (VNS) is thus potentially huge and has already been demonstrated in epilepsy. However, side effects are often elicited, in addition to the targeted neuromodulation.

APPROACH

This review examines the state of the art of VNS applied to two emerging modulations of autonomic function: heart failure and obesity, especially morbid obesity.

MAIN RESULTS

We report that VNS may benefit from improved stimulation delivery using very advanced technologies. However, most of the results from fundamental animal studies still need to be demonstrated in humans.

Non-Invasive Neuromodulation for Headache Disorders

Migraine and other chronic headache disorders are common and if inadequately treated, can lead to significant disability. The effectiveness of medications can be limited by side effects, drug interactions, and comorbid diseases necessitating alternative methods. Technological developments in the past 5 years have made it possible to use non-invasive methods of neuromodulation to treat primary headache disorders. This field includes technologies such as supraorbital transcutaneous stimulation (STS), transcranial magnetic stimulation (TMS), and non-invasive vagal nerve stimulation (nVNS). Existing trials show these modalities are safe and well tolerated and can be combined with standard pharmacotherapy. We review the technologies, biological rationales, and trials involving non-invasive neuromodulation for the treatment of primary headache disorders.