Brain imaging correlates of peripheral nerve stimulation

Nonpharmacologic Treatments for Chronic and Episodic Migraine: A Systematic Review and Meta-Analysis

BACKGROUND

Minimally invasive techniques for treatment-resistant migraine have been developed on recent insights into the peripheral pathogenesis of migraines. Although there is a growing body of evidence supporting these techniques, no study has yet compared the effects of these treatments on headache frequency, severity, duration, and cost.

METHODS

PubMed, Embase, and Cochrane Library databases were searched to identify randomized placebo-controlled trials that compared radiofrequency ablation, botulinum toxin type A (BT-A), nerve block, neurostimulation, or migraine surgery to placebo for preventive treatment. Data on changes from baseline to follow-up in headache frequency, severity, duration, and quality of life were analyzed.

RESULTS

A total of 30 randomized controlled trials and 2680 patients were included. Compared with placebo, there was a significant decrease in headache frequency in patients with nerve block ( P = 0.04) and surgery ( P < 0.001). Headache severity decreased in all treatments. Duration of headaches was significantly reduced in the BT-A ( P < 0.001) and surgery cohorts ( P = 0.01). Quality of life improved significantly in patients with BT-A, nerve stimulator, and migraine surgery. Migraine surgery had the longest lasting effects (11.5 months) compared with nerve ablation (6 months), BT-A (3.2 months), and nerve block (11.9 days).

CONCLUSIONS

Migraine surgery is a cost-effective, long-term treatment to reduce headache frequency, severity, and duration without significant risk of complication. BT-A reduces headache severity and duration, but it is short-lasting and associated with greater adverse events and lifetime cost. Although efficacious, radiofrequency ablation and implanted nerve stimulators have high risks of adverse events and explantation, whereas benefits of nerve blocks are short in duration.

The Mystery of Mental Integrity: Clarifying Its Relevance to Neurotechnologies

The concept of mental integrity is currently a significant topic in discussions concerning the regulation of neurotechnologies. Technologies such as deep brain stimulation and brain-computer interfaces are believed to pose a unique threat to mental integrity, and some authors have advocated for a legal right to protect it. Despite this, there remains uncertainty about what mental integrity entails and why it is important. Various interpretations of the concept have been proposed, but the literature on the subject is inconclusive. Here we consider a number of possible interpretations and argue that the most plausible one concerns neurotechnologies that bypass one's reasoning capacities, and do so specifically in ways that reliably lead to alienation from one's mental states. This narrows the scope of what constitutes a threat to mental integrity and offers a more precise role for the concept to play in the ethical evaluation of neurotechnologies.

Primary headache disorders: From pathophysiology to neurostimulation therapies

Primary headache disorders including migraine, cluster headache, and tension-type headache are among the most common disabling diseases worldwide. The unclear pathogenesis of primary headache disorders has led to high rates of misdiagnosis and limited available treatment options. In this review, we have summarized the pathophysiological factors for a better understanding of primary headache disorders. Advances in functional neuroimaging, genetics, neurophysiology have indicated that cortical hyperexcitability, regional brain dysfunction, central sensitization and neuroplasticity changes play vital roles in the development of primary headache disorders. Moreover, we have also discussed a series of neurostimulation approaches with their stimulation mechanism, safety and efficacy for prevention and treatment of primary headache disorders. Noninvasive or implantable neurostimulation techniques show great promise for treating refractory primary headache disorders.

Mechanism of Action of Peripheral Nerve Stimulation for Chronic Pain: A Narrative Review

The use of stimulation of peripheral nerves to test or treat various medical disorders has been prevalent for a long time. Over the last few years, there has been growing evidence for the use of peripheral nerve stimulation (PNS) for treating a myriad of chronic pain conditions such as limb mononeuropathies, nerve entrapments, peripheral nerve injuries, phantom limb pain, complex regional pain syndrome, back pain, and even fibromyalgia. The ease of placement of a minimally invasive electrode via percutaneous approach in the close vicinity of the nerve and the ability to target various nerves have led to its widespread use and compliance. While most of the mechanism behind its role in neuromodulation is largely unknown, the gate control theory proposed by Melzack and Wall in the 1960s has been the mainstay for understanding its mechanism of action. In this review article, the authors performed a literature review to discuss the mechanism of action of PNS and discuss its safety and usefulness in treating chronic pain. The authors also discuss current PNS devices available in the market today.

Arousal States as a Key Source of Variability in Speech Perception and Learning

The human brain exhibits the remarkable ability to categorize speech sounds into distinct, meaningful percepts, even in challenging tasks like learning non-native speech categories in adulthood and hearing speech in noisy listening conditions. In these scenarios, there is substantial variability in perception and behavior, both across individual listeners and individual trials. While there has been extensive work characterizing stimulus-related and contextual factors that contribute to variability, recent advances in neuroscience are beginning to shed light on another potential source of variability that has not been explored in speech processing. Specifically, there are task-independent, moment-to-moment variations in neural activity in broadly-distributed cortical and subcortical networks that affect how a stimulus is perceived on a trial-by-trial basis. In this review, we discuss factors that affect speech sound learning and moment-to-moment variability in perception, particularly arousal states—neurotransmitter-dependent modulations of cortical activity. We propose that a more complete model of speech perception and learning should incorporate subcortically-mediated arousal states that alter behavior in ways that are distinct from, yet complementary to, top-down cognitive modulations. Finally, we discuss a novel neuromodulation technique, transcutaneous auricular vagus nerve stimulation (taVNS), which is particularly well-suited to investigating causal relationships between arousal mechanisms and performance in a variety of perceptual tasks. Together, these approaches provide novel testable hypotheses for explaining variability in classically challenging tasks, including non-native speech sound learning.

Vagus nerve stimulation does not alter brainstem nuclei morphology in patients with refractory epilepsy

OBJECTIVE

To describe morphological characteristics of the brainstem nuclei in response to chronic vagus nerve stimulation (VNS) in patients with refractory epilepsy.

BACKGROUND

VNS is a treatment option for individuals with medically refractory epilepsy. While treatment with VNS may achieve up to 50% seizure reduction and is protective against sudden unexpected death in epilepsy (SUDEP), its mechanism of action is not fully understood. Long-term structural and cellular changes in response to VNS have rarely been addressed in humans.

METHODS

Four autopsy cases with history of chronic epilepsy treated with VNS (VNS+) and 4 age- and sex-matched chronic epilepsy-related death cases without VNS (VNS-) were included. Detailed clinical and postmortem data were obtained. Serial horizontal sections of the brainstem were prepared and stained with hematoxylin, eosin, and luxol fast blue (HE/LFB). Three regions of interest (ROIs) were delineated, including nucleus tractus solitarius (NTS), locus coeruleus (LC), and the rostral pontine group of raphe nuclei (rRN). Immunohistochemistry studies were performed using antibodies to GFAP, NeuN, HLA-DR, and IBA-1. Immunolabeling index was analyzed.

RESULTS

Three of the 4 VNS+ patients and all 4 control (VNS-) patients died of SUDEP. There was no laterality difference in the NeuN, GFAP, HLA-DR and IBA-1 expression in LC and NTS of VNS+ patients. Similarly, there was no difference in the rRN, LC, and NTS between the VNS+ and VNS- groups.

CONCLUSION

This study represents the first histopathological study of the long-term effects of VNS therapy in the human brain. There was no difference observed in the neuronal cell number, degree of astrocytosis, and neuroinflammation in the main brainstem vagal afferent nuclei after prolonged VNS treatment in patients with refractory epilepsy.

SPECT imaging of cerebral blood flow changes induced by acute trigeminal nerve stimulation in drug-resistant epilepsy. A pilot study

OBJECTIVE

To explore the cortical areas targeted by acute transcutaneous trigeminal nerve stimulation (TNS) in patients with drug-resistant epilepsy (DRE) using single photon emission computed tomography (SPECT).

METHODS

Ten patients with DRE underwent brain SPECT at baseline and immediately after a 20-minute TNS (0.25 ms; 120 Hz; 30 s ON and 30 s OFF) applied bilaterally to the infraorbital nerve. The French Color Standard International Scale was used for qualitative analyses and z-scores were used to calculate the Odds Ratio (OR).

RESULTS

At baseline global hypoperfusion (mainly in temporo-mesial, temporo-parietal and fronto-temporal and temporo-occipital areas) was detected in all patients. Following TNS, a global increase in cortical tracer uptake and a significant decrease in median hypoperfusion score were observed. A significant effect favoring a general TNS-induced increase in cortical perfusion (OR = 4.96; p = 0.0005) was detected in 70% of cases, with significant effects in the limbic (p = 0.003) and temporal (p = 0.003) lobes. Quantitative analyses of z-scores confirmed significant TNS-induced increases in perfusion in the temporal (+0.59 SDs; p = 0.001), and limbic (+0.43 SDs; p = 0.03) lobes.

CONCLUSION

Short-term TNS is followed a global increase in cortical perfusion, namely in the temporal and limbic lobes.

SIGNIFICANCE

The TNS-induced perfusion increase may reflect neurons' activity changes in cortical areas implicated in the epilepsy network.

Mechanism of Peripheral Nerve Stimulation in Chronic Pain

INTRODUCTION

With the advancement of technology, peripheral nerve stimulation (PNS) has been increasingly used to treat various chronic pain conditions. Its origin is based on the gate control theory postulated by Wall and Melzack in 1965. However, the exact mechanism behind PNS' analgesic effect is largely unknown. In this article, we performed a comprehensive literature review to overview the PNS mechanism of action.

DESIGN

A comprehensive literature review on the mechanism of PNS in chronic pain.

METHODS

Comprehensive review of the available literature on the mechanism of PNS in chronic pain. Data were derived from database searches of PubMed, Scopus, and the Cochrane Library and manual searches of bibliographies and known primary or review articles.

RESULTS

Animal, human, and imaging studies have demonstrated the peripheral and central analgesic mechanisms of PNS by modulating the inflammatory pathways, the autonomic nervous system, the endogenous pain inhibition pathways, and involvement of the cortical and subcortical areas.

CONCLUSIONS

Peripheral nerve stimulation exhibits its neuromodulatory effect both peripherally and centrally. Further understanding of the mechanism of PNS can help guide stimulation approaches and parameters to optimize the use of PNS.

Vagus nerve stimulation and Neurotrophins: a biological psychiatric perspective

Since 2004, vagus nerve stimulation (VNS) has been used in treatment-resistant or treatment-intolerant depressive episodes. Today, VNS is suggested as possible therapy for a larger spectrum of psychiatric disorders, including schizophrenia, obsessive compulsive disorders, and panic disorders. Despite a large body of literature supports the application of VNS in patients' treatment, the exact mechanism of action of VNS remains not fully understood. In the present study, the major knowledges on the brain areas and neuronal pathways regulating neuroimmune and autonomic response subserving VNS effects are reviewed. Furthermore, the involvement of the neurotrophins (NTs) Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) in vagus nerve (VN) physiology and stimulation is revised. The data on brain NGF/BDNF synthesis and in turn on the activity-dependent plasticity, connectivity rearrangement and neurogenesis, are presented and discussed as potential biomarkers for optimizing stimulatory parameters for VNS. A vagus nerve-neurotrophin interaction model in the brain is finally proposed as a working hypothesis for future studies addressed to understand pathophysiology of psychiatric disturbance.

Double Blinded Randomized Trial of Subcutaneous Trigeminal Nerve Stimulation as Adjuvant Treatment for Major Unipolar Depressive Disorder

BACKGROUND

More than 30% of major depressive disorder patients fail to respond to adequate trials of medications and psychotherapy. While modern neuromodulation approaches (ie, vagal nerve stimulation, deep brain stimulation) are yet to prove their efficacy for such cases in large randomized controlled trials, trigeminal nerve stimulation (TNS) has emerged as an alternative with promising effects on mood disorders.

OBJECTIVE

To assess efficacy, safety, tolerability, and placebo effect duration of continuous subcutaneous TNS (sTNS) in treatment-resistant depression (TRD).

METHODS

The TREND study is a single-center, double-blind, randomized, controlled, phase II clinical trial. Twenty unipolar TRD patients will receive V1 sTNS as adjuvant to medical therapy and randomized to active vs sham stimulation throughout a 24-wk period. An additional 24-wk open-label phase will follow. Data concerning efficacy, placebo response, relapse, and side effects related to surgery or electrical stimulation will be recorded. We will use the HDRS-17, BDI-SR, IDS_SR30, and UKU scales.

EXPECTED OUTCOMES

The main outcome measure is improvement in depression scores using HAM-17 under continuous sTNS as adjuvant to antidepressants. Active stimulation is expected to significantly impact response and remission rates. Minor side effects are expected due to the surgical procedure and electrical stimulation. The open-label phase should further confirm efficacy and tolerability.

DISCUSSION

This study protocol is designed to define efficacy of a novel adjuvant therapy for TRD. We must strive to develop safe, reproducible, predictable, and well-tolerated neuromodulation approaches for TRD patients impaired to manage their lives and contribute with society.

Cerebral metabolism before and after external trigeminal nerve stimulation in episodic migraine

Background and aim A recent sham-controlled trial showed that external trigeminal nerve stimulation (eTNS) is effective in episodic migraine (MO) prevention. However, its mechanism of action remains unknown. We performed 18-fluorodeoxyglucose positron emission tomography (FDG-PET) to evaluate brain metabolic changes before and after eTNS in episodic migraineurs. Methods Twenty-eight individuals were recruited: 14 with MO and 20 healthy volunteers (HVs). HVs underwent a single FDG-PET, whereas patients were scanned at baseline, directly after a first prolonged session of eTNS (Cefaly®) and after three months of treatment (uncontrolled study). Results The frequency of migraine attacks significantly decreased in compliant patients ( N = 10). Baseline FDG-PET revealed a significant hypometabolism in fronto-temporal areas, especially in the orbitofrontal (OFC) and rostral anterior cingulate cortices (rACC) in MO patients. This hypometabolism was reduced after three months of eTNS treatment. Conclusion Our study shows that metabolic activity of OFC and rACC, which are pivotal areas in central pain and behaviour control, is decreased in migraine. This hypometabolism is reduced after three months of eTNS. eTNS might thus exert its beneficial effects via slow neuromodulation of central pain-controlling areas, a mechanism also previously reported in chronic migraine and cluster headache after percutaneous occipital nerve stimulation. However, this finding needs to be confirmed by further studies using a sham condition.

Effects of chronic abdominal vagal stimulation of small-diameter neurons on brain metabolism and food intake

BACKGROUND

Abdominal bilateral vagal stimulation reduces food intake in animals. However, the classical square wave, mA range current generator is poorly effective to evoke action potentials on A∂ and C neurons that represent the majority of vagal neurons at the abdominal level.

OBJECTIVE/HYPOTHESIS

METHODS: The current thresholds for pulsons (S2 & S3) and millisecond pulses (S1) required to trigger action potentials were calculated in 5 anaesthetized pigs using single fibre recording. Similar stimulation protocols were compared chronically to sham stimulation in 24 pigs. After two weeks of chronic stimulation, food intake and brain metabolism were investigated. The electrical characteristics and histology of the vagus nerve were also studied.

RESULTS

S3 stimulation required a lower amount of charges to trigger an action potential. Chronically applied S2 & S3 activated the dorsal vagal complex and increased the metabolism of its afferent cortical structures. They also reduced energy intake together with a reduced ingestion of high fat and high sugar diets. All these effects were not observed for the S1 group. The vagal histology for the S1, S2 and S3 groups was not different from that of the sham.

CONCLUSIONS

These findings demonstrate that pulsons applied bilaterally on the abdominal vagus reduced food intake as a consequence of the activation of the brainstem and higher-order brain areas.

Obesity-Associated Alterations in Glucose Metabolism Are Reversed by Chronic Bilateral Stimulation of the Abdominal Vagus Nerve

Acute vagal stimulation modifies glucose and insulin metabolism, but the effect of chronic bilateral vagal stimulation is not known. Our aim was to quantify the changes in whole-body and organ-specific insulin sensitivities 12 weeks after permanent, bilateral, vagal stimulation performed at the abdominal level in adult mini-pigs. In 15 adult mini-pigs, stimulating electrodes were placed around the dorsal and ventral vagi using laparoscopy and connected to a dual-channel stimulator placed subcutaneously. Animals were divided into three groups based on stimulation and body weight (i.e., lean nonstimulated, obese nonstimulated, and obese stimulated). Twelve weeks after surgery, glucose uptake and insulin sensitivity were measured using positron emission tomography during an isoglycemic clamp. Mean whole-body insulin sensitivity was lower by 34% (P < 0.01) and the hepatic glucose uptake rate was lower by 33% (P < 0.01) in obese-nonstimulated mini-pigs but was no different in obese-stimulated compared with lean mini-pigs. An improvement in skeletal glucose uptake rate was also observed in obese-stimulated compared with obese-nonstimulated groups (P < 0.01). Vagal stimulation was associated with increased glucose metabolism in the cingulate and prefrontal brain areas. We conclude that chronic vagal stimulation improves insulin sensitivity substantially in diet-induced obesity by both peripheral and central mechanisms.

Unilateral occipital nerve stimulation for bilateral occipital neuralgia: a case report and literature review

Objectives

The aim of this study is to present a case of successful relief of bilateral occipital neuralgia (ON) using unilateral occipital nerve stimulation (ONS) and to discuss the possible underlying mechanisms.

Materials and methods

We present the case of a 59-year-old female patient with severe bilateral ON treated with unilateral ONS. We systematically reviewed previous studies of ONS for ON, discussing the possible mechanisms of ONS in the relief of ON.

Results

The patient reported complete pain relief after consistent unilateral ONS during the follow-up period. The underlying mechanisms may be linked to the relationship between pain and several brain regions, including the pons, midbrain, and periaqueductal gray.

Conclusion

ONS is an effective and safe option for treating ON. Future studies will be required to clarify the mechanisms by which unilateral occipital stimulation provided relief for bilateral neuralgia in this case.

Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain

PURPOSE

This review summarises the need for MRI with in situ neuromodulation, the key safety challenges and how they may be mitigated, and surveys the current status of MRI safety for the main categories of neuro-stimulation device, including deep brain stimulation, vagus nerve stimulation, sacral neuromodulation, spinal cord stimulation systems, and cochlear implants.

REVIEW SUMMARY

When neuro-stimulator systems are introduced into the MRI environment a number of hazards arise with potential for patient harm, in particular the risk of thermal injury due to MRI-induced heating. For many devices however, safe MRI conditions can be determined, and MRI safely performed, albeit with possible compromise in anatomical coverage, image quality or extended acquisition time.

CONCLUSIONS

The increasing availability of devices conditional for 3 T MRI, whole-body transmit imaging, and imaging in the on-stimulation condition, will be of significant benefit to the growing population of patients benefitting from neuromodulation therapy, and open up new opportunities for functional imaging research.

Vagus Nerve and Vagus Nerve Stimulation, a Comprehensive Review: Part III

Vagus nerve stimulation (VNS) is currently undergoing multiple trials to explore its potential for various clinical disorders. To date, VNS has been approved for the treatment of refractory epilepsy and depression. It exerts antiepileptic or antiepileptogenic effect possibly through neuromodulation of certain monoamine pathways. Beyond epilepsy, VNS is also under investigation for the treatment of inflammation, asthma, and pain. VNS influences the production of inflammatory cytokines to dampen the inflammatory response. It triggers the systemic release of catecholamines that alleviates the asthma attack. VNS induces antinociception by modulating multiple pain-associated structures in the brain and spinal cord affecting peripheral/central nociception, opioid response, inflammation process, autonomic activity, and pain-related behavior. Progression in VNS clinical efficacy over time suggests an underlying disease-modifying neuromodulation, which is an emerging field in neurology. With multiple potential clinical applications, further development of VNS is encouraging.

Diagnosis and treatment of faecal incontinence: Consensus statement of the Italian Society of Colorectal Surgery and the Italian Association of Hospital Gastroenterologists

Faecal incontinence is a common and disturbing condition, which leads to impaired quality of life and huge social and economic costs. Although recent studies have identified novel diagnostic modalities and therapeutic options, the best diagnostic and therapeutic approach is not yet completely known and shared among experts in this field. The Italian Society of Colorectal Surgery and the Italian Association of Hospital Gastroenterologists selected a pool of experts to constitute a joint committee on the basis of their experience in treating pelvic floor disorders. The aim was to develop a position paper on the diagnostic and therapeutic aspects of faecal incontinence, to provide practical recommendations for a cost-effective diagnostic work-up and a tailored treatment strategy. The recommendations were defined and graded on the basis of levels of evidence in accordance with the criteria of the Oxford Centre for Evidence-Based Medicine, and were based on currently published scientific evidence. Each statement was drafted through constant communication and evaluation conducted both online and during face-to-face working meetings. A brief recommendation at the end of each paragraph allows clinicians to find concise responses to each diagnostic and therapeutic issue.

Trigeminal branch stimulation for the treatment of intractable craniofacial pain

OBJECT

Trigeminal branch stimulation has been used in the treatment of craniofacial pain syndromes. The risks and benefits of such an approach have not been clearly delineated in large studies, however. The authors report their experience in treating craniofacial pain with trigeminal branch stimulation and share the lessons they have learned after 93 consecutive electrode placements.

METHODS

A retrospective review of all patients who underwent trigeminal branch electrode placement by the senior author (C.J.W.) for the treatment of craniofacial pain was performed.

RESULTS

Thirty-five patients underwent implantation of a total of 93 trial and permanent electrodes between 2006 and 2013. Fifteen patients who experienced improved pain control after trial stimulation underwent implantation of permanent stimulators and were followed for an average of 15 months. At last follow-up 73% of patients had improvement in pain control, whereas only 27% of patients had no pain improvement. No serious complications were seen during the course of this study.

CONCLUSIONS

Trigeminal branch stimulation is a safe and effective treatment for a subset of patients with intractable craniofacial pain.

Acupuncture for refractory epilepsy: role of thalamus

Neurostimulation procedures like vagus nerve stimulation (VNS) and deep brain stimulation have been used to treat refractory epilepsy and other neurological disorders. While holding promise, they are invasive interventions with serious complications and adverse effects. Moreover, their efficacies are modest with less seizure free. Acupuncture is a simple, safe, and effective traditional healing modality for a wide range of diseases including pain and epilepsy. Thalamus takes critical role in sensory transmission and is highly involved in epilepsy genesis particularly the absence epilepsy. Considering thalamus serves as a convergent structure for both acupuncture and VNS and the thalamic neuronal activities can be modulated by acupuncture, we propose that acupuncture could be a promising therapy or at least a screening tool to select suitable candidates for those invasive modalities in the management of refractory epilepsy.

Innervation of the cerebral dura mater

The trigemino-cardiac reflex during Onyx embolization for dural arteriovenous fistula may be caused by mechanical or chemical stimulus to the terminals of the unencapsulated Ruffini-like receptors stemming from A-axons in the dural connective tissue at sites of dural arteries and sinuses. Slow A (Aδ) and fast A (Aβ) neurons may play a role in the stimulus afferent pathway due to their higher mechanosensitivity and chemosensitivity. These afferent pathway nerves are cholinergic innervations of the dura mater, which also contains vasoactive neuropeptides such as calcitonin gene-related peptide, substance P, and neurokinin A. Stimulation of meningeal sensory fibres can evoke cerebral vasodilation through the peripheral release of neuropeptides, which play a role in headache pathogenesis. These myelinated A-fibers terminate in the deep part (laminae III-V) of the spinal dorsal horn. Its efferent pathway has been defined as the acetylcholinergic vagus nerve. The A11 nucleus, located in the posterior hypothalamus, providing the only known source of descending dopaminergic innervation for the spinal grey matter, can inhibit the neurons in the spinal dorsal horn.