EEG changes with vagus nerve stimulation

Vagus Nerve Stimulation Therapy for Drug-Resistant Epilepsy in Children-A Literature Review

Vagus nerve stimulation (VNS) is a palliative treatment for drug-resistant epilepsy (DRE) that has been in use for over two decades. VNS suppresses epileptic seizures, prevents emotional disorders, and improves cognitive function and sleep quality, a parallel effect associated with the control of epileptic seizures. The seizure suppression rate with VNS increases monthly to annually, and the incidence of side effects reduces over time. This method is effective in treating DRE in children as well as adults, such as epilepsy associated with tuberous sclerosis, Dravet syndrome, and Lennox-Gastaut syndrome. In children, it has been reported that seizures decreased by >70% approximately 8 years after initiating VNS, and the 50% responder rate was reported to be approximately 70%. VNS regulates stimulation and has multiple useful systems, including self-seizure suppression using magnets, additional stimulation using an automatic seizure detection system, different stimulation settings for day and night, and an automatic stimulation adjustment system that reduces hospital visits. VNS suppresses seizures and has beneficial behavioral effects in children with DRE. This review describes the VNS system, the mechanism of the therapeutic effect, the specific stimulation adjustment method, antiepileptic effects, and other clinical effects in patients with childhood DRE.

Effect of Vagus Nerve Stimulation on the GASH/Sal Audiogenic-Seizure-Prone Hamster

Vagus nerve stimulation (VNS) is an adjuvant neuromodulation therapy for the treatment of refractory epilepsy. However, the mechanisms behind its effectiveness are not fully understood. Our aim was to develop a VNS protocol for the Genetic Audiogenic Seizure Hamster from Salamanca (GASH/Sal) in order to evaluate the mechanisms of action of the therapy. The rodents were subject to VNS for 14 days using clinical stimulation parameters by implanting a clinically available neurostimulation device or our own prototype for laboratory animals. The neuroethological assessment of seizures and general behavior were performed before surgery, and after 7, 10, and 14 days of VNS. Moreover, potential side effects were examined. Finally, the expression of 23 inflammatory markers in plasma and the left-brain hemisphere was evaluated. VNS significantly reduced seizure severity in GASH/Sal without side effects. No differences were observed between the neurostimulation devices. GASH/Sal treated with VNS showed statistically significant reduced levels of interleukin IL-1β, monocyte chemoattractant protein MCP-1, matrix metalloproteinases (MMP-2, MMP-3), and tumor necrosis factor TNF-α in the brain. The described experimental design allows for the study of VNS effects and mechanisms of action using an implantable device. This was achieved in a model of convulsive seizures in which VNS is effective and shows an anti-inflammatory effect.

The effects of Vagal Nerve Stimulation on time perception in epilepsy patients

In this study, it was aimed to investigate the effects of switching off stimulation on time perception in patients with drug-resistant epilepsy who underwent Vagal Nerve Stimulation (VNS). In accordance with the literature, a cognitive battery of tests for motor timing and perceptual timing was utilized. Computerized time perception tests; Paced Motor Timing Test, Duration Discrimination Test, Temporal Reproduction Test, and Time Estimation Test were administered to the patients while VNS was on and off. A total of 14 patients who met the inclusion criteria of 23 VNS patients followed in the Epilepsy Outpatient Clinic were included in the study. In the Temporal Reproduction Test, for time durations of 1000 ms (ms), 2000 ms, 3000 ms, 4000 ms, and 5000 ms the comparison of reported time values between VNS on and VNS off yielded respective p values; p = 0.73, p = 0.03, p = 0.176, p = 0.418, p = 0,873. The reported time is thus significantly shorter only for 2000 ms when the VNS was on. Positive effect of VNS on attention, alertness and focusing are expected to cause acceleration of the internal clock resulting in perceiving time running slower than actual. In our study, it was concluded that the internal clock runs faster when the VNS is on, and time is perceived as running slower than it actually is. This result can also be accepted as an indirect indicator of increased attention in the period when VNS is on.

Novel therapeutic strategies in glioma targeting glutamatergic neurotransmission

High grade gliomas carry a poor prognosis despite aggressive surgical and adjuvant approaches including chemoradiotherapy. Recent studies have demonstrated a mitogenic association between neuronal electrical activity and glioma growth involving the PI3K-mTOR pathway. As the predominant excitatory neurotransmitter of the brain, glutamate signalling in particular has been shown to promote glioma invasion and growth. The concept of the neurogliomal synapse has been established whereby glutamatergic receptors on glioma cells have been shown to promote tumour propagation. Targeting glutamatergic signalling is therefore a potential treatment option in glioma. Antiepileptic medications decrease excess neuronal electrical activity and some may possess anti-glutamate effects. Although antiepileptic medications continue to be investigated for an anti-glioma effect, good quality randomised trial evidence is lacking. Other pharmacological strategies that downregulate glutamatergic signalling include riluzole, memantine and anaesthetic agents. Neuromodulatory interventions possessing potential anti-glutamate activity include deep brain stimulation and vagus nerve stimulation - this contributes to the anti-seizure efficacy of the latter and the possible neuroprotective effect of the former. A possible role of neuromodulation as a novel anti-glioma modality has previously been proposed and that hypothesis is extended to include these modalities. Similarly, the significant survival benefit in glioblastoma attributable to alternating electrical fields (Tumour Treating Fields) may be a result of disruption to neurogliomal signalling. Further studies exploring excitatory neurotransmission and glutamatergic signalling and their role in glioma origin, growth and propagation are therefore warranted.

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.

Investigation of the effectiveness of vagus nerve stimulation for pediatric drug-resistant epilepsies secondary to nonaccidental trauma

PURPOSE

Epilepsy following non-accidental trauma (NAT) occurs in 18% of pediatric patients. About 33% of patients with epilepsy develop drug-resistant epilepsy. For these patients, vagus nerve stimulation (VNS) is a palliative treatment option. We aimed to investigate the effectiveness of VNS among pediatric NAT-related epilepsy patients compared to those with non-NAT-related epilepsy.

METHODS

We performed an 11-year retrospective analysis of VNS implantations for drug-resistant epilepsy at UPMC Children's Hospital of Pittsburgh. Patients were split into two groups: NAT vs. non-NAT. The primary outcome was the attainment of ≥ 50% seizure frequency reduction at 1-year post-VNS implantation. Fisher's exact tests and Wilcoxon rank-sum tests were used to compare groups. Significance was assessed at the alpha = 0.05 level.

RESULTS

This analysis included data from 370 pediatric VNS patients, of whom 9 had NAT-related epilepsy. NAT patients had a significantly younger age of epilepsy onset than non-NAT patients (0.3 years vs. 3.3 years). Otherwise, there were no statistically significant baseline differences between groups, including patient sex and quantity of antiseizure medications pre-VNS. Overall, 71% of NAT patients experienced ≥ 50% seizure frequency reduction compared to 48% of non-NAT patients (p = 0.269).

CONCLUSION

VNS may allow a higher proportion of pediatric patients with NAT-related epilepsy to achieve ≥ 50% seizure frequency reduction compared to other epilepsy etiologies. While the results of this study were not statistically significant, the effect size was large. Our results underscore the need for larger, multi-center studies to validate the effectiveness of VNS for this patient population.

Latest Views on the Mechanisms of Action of Surgically Implanted Cervical Vagal Nerve Stimulation in Epilepsy

BACKGROUND

Vagus nerve stimulation (VNS) is approved as an adjunctive treatment for drug-resistant epilepsy. Although there is a substantial amount of literature aiming at unraveling the mechanisms of action of VNS in epilepsy, it is still unclear how the cascade of events triggered by VNS leads to its antiepileptic effect.

OBJECTIVE

In this review, we integrated available peer-reviewed data on the effects of VNS in clinical and experimental research to identify those that are putatively responsible for its therapeutic effect. The topic of transcutaneous VNS will not be covered owing to the current lack of data supporting the differences and commonalities of its mechanisms of action in relation to invasive VNS.

SUMMARY OF THE MAIN FINDINGS

There is compelling evidence that the effect is obtained through the stimulation of large-diameter afferent myelinated fibers that project to the solitary tract nucleus, then to the parabrachial nucleus, which in turn alters the activity of the limbic system, thalamus, and cortex. VNS-induced catecholamine release from the locus coeruleus in the brainstem plays a pivotal role. Functional imaging studies tend to point toward a common vagal network that comes into play, made up of the amygdalo-hippocampal regions, left thalamus, and insular cortex.

CONCLUSIONS

Even though some crucial pieces are missing, neurochemical, molecular, cellular, and electrophysiological changes occur within the vagal afferent network at three main levels (the brainstem, the limbic system [amygdala and hippocampus], and the cortex). At this final level, VNS notably alters functional connectivity, which is known to be abnormally high within the epileptic zone and was shown to be significantly decreased by VNS in responders. The effect of crucial VNS parameters such as frequency or current amplitude on functional connectivity metrics is of utmost importance and requires further investigation.

Evolution of the Vagus Nerve Stimulation (VNS) Therapy System Technology for Drug-Resistant Epilepsy

The vagus nerve stimulation (VNS) Therapy® System is the first FDA-approved medical device therapy for the treatment of drug-resistant epilepsy. Over the past two decades, the technology has evolved through multiple iterations resulting in software-related updates and implantable lead and generator hardware improvements. Healthcare providers today commonly encounter a range of single- and dual-pin generators (models 100, 101, 102, 102R, 103, 104, 105, 106, 1000) and related programming systems (models 250, 3000), all of which have their own subtle, but practical differences. It can therefore be a daunting task to go through the manuals of these implant models for comparison, some of which are not readily available. In this review, we highlight the technological evolution of the VNS Therapy System with respect to device approval milestones and provide a comparison of conventional open-loop vs. the latest closed-loop generator models. Battery longevity projections and an in-depth examination of stimulation mode interactions are also presented to further differentiate amongst generator models.

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.

Transcutaneous auricular VNS applied to experimental pain: A paired behavioral and EEG study using thermonociceptive CO2 laser

Background

Transcutaneous auricular Vagal Nerve Stimulation (taVNS) is a non-invasive neurostimulation technique with potential analgesic effects. Several studies based on subjective behavioral responses suggest that taVNS modulates nociception differently with either pro-nociceptive or anti-nociceptive effects.

Objective

This study aimed to characterize how taVNS alters pain perception, by investigating its effects on event-related potentials (ERPs) elicited by different types of spinothalamic and lemniscal somatosensory stimuli, combined with quantitative sensory testing (detection threshold and intensity ratings).

Methods

We performed 3 experiments designed to study the time-dependent effects of taVNS and compare with standard cervical VNS (cVNS). In Experiment 1, we assessed the effects of taVNS after 3 hours of stimulation. In Experiment 2, we focused on the immediate effects of the duty cycle (OFF vs. ON phases). Experiments 1 and 2 included 22 and 15 healthy participants respectively. Both experiments consisted of a 2-day cross-over protocol, in which subjects received taVNS and sham stimulation sequentially. In addition, subjects received a set of nociceptive (thermonociceptive CO₂ laser, mechanical pinprick) and non-nociceptive (vibrotactile, cool) stimuli, for which we recorded detection thresholds, intensity of perception and ERPs. Finally, in Experiment 3, we tested 13 epileptic patients with an implanted cVNS by comparing OFF vs. ON cycles, using a similar experimental procedure.

Results

Neither taVNS nor cVNS appeared to modulate the cerebral and behavioral aspects of somatosensory perception.

Conclusion

The potential effect of taVNS on nociception requires a cautious interpretation, as we found no objective change in behavioral and cerebral responses to spinothalamic and lemniscal somatosensory stimulations.

Transcutaneous vagus nerve stimulation in the treatment of drug-resistant epilepsy

Epilepsy is a common chronic neurological disease with a high burden of illness. Invasive vagus nerve stimulation (iVNS) is a well-established treatment option in patients with epilepsy (PWE). More recently, transcutaneous vagus nerve stimulation (tVNS) was introduced, an alternative option which is particularly interesting because it does not require surgery and is instantaneously removable. Here, we thoroughly reviewed clinical data on efficacy and safety of tVNS in epilepsies. Five prospective trials in 118 patients with drug-resistant epilepsies and 3 randomized controlled trials in 280 patients with drug-resistant epilepsies were carried out. Study protocols were heterogeneous in terms of patients' characteristics, used device, stimulation parameters, study duration and endpoints. Seizure reduction amounted up to 64%, with responder rates (seizure reduction ≥50%) up to 65%. Seizure freedom was reached in up to 24%, and even to 31% in a small pediatric study group. Seizure severity scores were provided in 4 studies, showing significant improvement in two of them. Adverse side effects were mostly headache, ear pain and skin alteration and rated as mild to moderate. Drowsiness might be depend on stimulation intensity. Quality of life scores reflecting burden of illness showed significant improvement in two studies. Efficacy and safety of tVNS in PWE has to be interpreted as promising. Multicenter randomized double-blind clinical trials with standardized stimulation protocols and long-term follow-up studies are necessary to finally assess tVNS treatment outcome in drug-resistant epilepsies.

Transcutaneous auricular vagus nerve stimulation induces stabilizing modifications in large-scale functional brain networks: towards understanding the effects of taVNS in subjects with epilepsy

Transcutaneous auricular vagus nerve stimulation (taVNS) is a novel non-invasive brain stimulation technique considered as a potential supplementary treatment option for subjects with refractory epilepsy. Its exact mechanism of action is not yet fully understood. We developed an examination schedule to probe for immediate taVNS-induced modifications of large-scale epileptic brain networks and accompanying changes of cognition and behaviour. In this prospective trial, we applied short-term (1 h) taVNS to 14 subjects with epilepsy during a continuous 3-h EEG recording which was embedded in two standardized neuropsychological assessments. From these EEG, we derived evolving epileptic brain networks and tracked important topological, robustness, and stability properties of networks over time. In the majority of investigated subjects, taVNS induced measurable and persisting modifications in network properties that point to a more resilient epileptic brain network without negatively impacting cognition, behaviour, or mood. The stimulation was well tolerated and the usability of the device was rated good. Short-term taVNS has a topology-modifying, robustness- and stability-enhancing immediate effect on large-scale epileptic brain networks. It has no detrimental effects on cognition and behaviour. Translation into clinical practice requires further studies to detail knowledge about the exact mechanisms by which taVNS prevents or inhibits seizures.

Combined use of the ketogenic diet and vagus nerve stimulation in pediatric drug-resistant epilepsy

Objective

Patients with drug-resistant epilepsy (DRE) pose considerable management challenges for patients, their families, and providers. Both the vagus nerve stimulator (VNS) and the ketogenic diet (KD) have been shown to be safe and effective in treating DRE. Nevertheless, information is lacking regarding treatment with combination of both modalities. This study reports the efficacy and tolerability of combining VNS and KD in a pediatric cohort with intractable epilepsy.

Methods

This is a retrospective review of 33 patients (0-17 years) with DRE treated with VNS and KD at a single pediatric level IV epilepsy center. We compared seizure reduction rates for each patient at baseline and at every clinic visit for 24 months after adding the second nonpharmacological therapy. The frequency of adverse events on the combined therapy was collected to assess safety and tolerability.

Results

There were a total of 170 visits for all patients while on the combined therapy. At 88% (95% CI: 83%-93%) of the visits, patients reported some reduction in seizure frequency. The proportion of patients reporting a greater than 50% seizure reduction over all visits was 62% (95% CI: 55%-69%). The proportion of a patient's visits with at least a greater than 50% reduction in seizure frequency had a median of 71% (IQR 33%-100%). Continued improvement was seen over time of combined treatment; for every one-unit time unit change (one month), there was a 6% increase in the odds of having a reduction in seizure frequency of >50% (OR = 1.06, 95% CI: 1.01-1.11).

Significance

This study shows that combining the VNS and KD in patients with drug-resistant epilepsy is well tolerated and reduces seizure frequency more than either one modality used alone and that the benefits in terms of seizure reduction continue to increase with the length of treatment.

Differential effects of vagus nerve stimulation paradigms guide clinical development for Parkinson's disease

BACKGROUND

Vagus nerve stimulation (VNS) modifies brain rhythms in the locus coeruleus (LC) via the solitary nucleus. Degeneration of the LC in Parkinson's disease (PD) is an early catalyst of the spreading neurodegenerative process, suggesting that stimulating LC output with VNS has the potential to modify disease progression. We previously showed in a lesion PD model that VNS delivered twice daily reduced neuroinflammation and motor deficits, and attenuated tyrosine hydroxylase (TH)-positive cell loss.

OBJECTIVE

The goal of this study was to characterize the differential effects of three clinically-relevant VNS paradigms in a PD lesion model.

METHODS

Eleven days after DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, noradrenergic lesion, administered systemically)/6-OHDA (6-hydroxydopamine, dopaminergic lesion, administered intrastriatally) rats were implanted with VNS devices, and received either low-frequency VNS, standard-frequency VNS, or high-frequency microburst VNS. After 10 days of treatment and behavioral assessment, rats were euthanized, right prefrontal cortex (PFC) was dissected for norepinephrine assessment, and the left striatum, bilateral substantia nigra (SN), and LC were sectioned for immunohistochemical detection of catecholamine neurons, α-synuclein, astrocytes, and microglia.

RESULTS

At higher VNS frequencies, specifically microburst VNS, greater improvements occurred in motor function, attenuation of TH-positive cell loss in SN and LC, and norepinephrine concentration in the PFC. Additionally, higher VNS frequencies resulted in lower intrasomal α-synuclein accumulation and glial density in the SN.

CONCLUSIONS

These data indicate that higher stimulation frequencies provided the greatest attenuation of behavioral and pathological markers in this PD model, indicating therapeutic potential for these VNS paradigms.

The Immediate Effects of Vagus Nerve Stimulation in Intractable Epilepsy: An Intra-operative Electrocorticographic Analysis

The purpose of this study was to investigate whether and how vagus nerve stimulation (VNS) reduces the epileptogenic activity in the bilateral cerebral cortex in patients with intractable epilepsy. We analyzed the electrocorticograms (ECoGs) of five patients who underwent callosotomy due to intractable epilepsy even after VNS implantation. We recorded ECoGs and analyzed power spectrum in both VNS OFF and ON phases. We counted the number of spikes and electrodes with epileptic spikes, distinguishing unilaterally and bilaterally hemispherically spread spikes as synchronousness of the epileptic spikes in both VNS OFF and ON phases. There were 24.80 ± 35.55 and 7.20 ± 9.93 unilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.157), and 35.8 ± 29.21 and 10.6 ± 13.50 bilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.027). The number of electrodes with unilaterally and bilaterally spread spikes in the VNS OFF and ON phases was 3.84 ± 2.13 and 3.59 ± 1.82 (P = 0.415), and 8.20 ± 3.56 and 6.89 ± 2.89 (P = 0.026), respectively. The ECoG background power spectra recordings in the VNS OFF and ON phases were also analyzed. The spectral power tended to be greater in the high-frequency band at VNS ON phase than OFF phase. This study showed the reduction of epileptogenic spikes and spread areas of the spikes by VNS as immediate effects, electrophysiologically.

Neurostimulation in the treatment of refractory and super-refractory status epilepticus

Status epilepticus (SE) is a life-threatening condition with a mortality of up to 60% in the advanced and comatose forms of SE. In one out of five adults, first and second line fails to control epileptic activity, leading to refractory status epilepticus (RSE) and in around 3% to super-refractory status epilepticus (SRSE), where SE continues despite anesthetic treatment for 24 h or more. In this rare but devastating condition, innovative and safe treatments are needed. In a recent review on the use of vagal nerve stimulation in RSE and SRSE, a 74% response rate for abrogation of SE was reported. Here, we review the currently available evidence supporting the use of neurostimulation, including vagal nerve stimulation, direct cortical stimulation, transcranial magnetic stimulation, electroconvulsive therapy, and deep brain stimulation in RSE and SRSE. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Continuous Intraoperative Monitoring of Temporal Lobe Epilepsy Surgery

BACKGROUND/AIMS

The monitoring of interictal epileptiform discharge rates (IEDRs) all along anterior temporal lobe resections (ATLRs) has never been reported. Here the effect of ATLR on continuous IEDR monitoring is described.

METHODS

IEDRs computed automatically during entire interventions were recorded in 34 patients (38.2%, 13/34 depth; 61.8%, 21/34 scalp electrodes only). Monitorings were invalidated when burst suppression occurred or if initial IEDRs were <5.

RESULTS

Monitoring was successful for 69.2% (9/13) of the patients with depth recordings and for 4.8% (1/21) of the patients with scalp recordings. Burst suppressions precluded it in 30.8% (4/13) of the depth and in 57.1% (12/21) of the scalp recordings. Initial IEDRs were <5 for 38.1% (8/21) of the scalp recordings. Significant IEDR decreases were observed in 8/10 patients with successful monitoring. These decreases started with resection of the superior temporal gyrus. IEDRs decreased further with amygdalohippocampectomy in 3/5 patients. At the 12-month follow-up, all patients with IEDR decreases remained seizure free; both patients without did not.

CONCLUSION

IEDR monitoring was possible with depth, but not with scalp electrodes. IEDR decreases started with resection of the superior temporal gyrus. A larger patient cohort is necessary to confirm the high predictive values of IEDR monitoring that could become a tool for surgery customization.

Seizure outcomes in nonresective epilepsy surgery: an update

In approximately 30 % of patients with epilepsy, seizures are refractory to medical therapy, leading to significant morbidity and increased mortality. Substantial evidence has demonstrated the benefit of surgical resection in patients with drug-resistant focal epilepsy, and in the present journal, we recently reviewed seizure outcomes in resective epilepsy surgery. However, not all patients are candidates for or amenable to open surgical resection for epilepsy. Fortunately, several nonresective surgical options are now available at various epilepsy centers, including novel therapies which have been pioneered in recent years. Ablative procedures such as stereotactic laser ablation and stereotactic radiosurgery offer minimally invasive alternatives to open surgery with relatively favorable seizure outcomes, particularly in patients with mesial temporal lobe epilepsy. For certain individuals who are not candidates for ablation or resection, palliative neuromodulation procedures such as vagus nerve stimulation, deep brain stimulation, or responsive neurostimulation may result in a significant decrease in seizure frequency and improved quality of life. Finally, disconnection procedures such as multiple subpial transections and corpus callosotomy continue to play a role in select patients with an eloquent epileptogenic zone or intractable atonic seizures, respectively. Overall, open surgical resection remains the gold standard treatment for drug-resistant epilepsy, although it is significantly underutilized. While nonresective epilepsy procedures have not replaced the need for resection, there is hope that these additional surgical options will increase the number of patients who receive treatment for this devastating disorder-particularly individuals who are not candidates for or who have failed resection.

The heart side of brain neuromodulation

Neuromodulation refers to invasive, minimally invasive or non-invasive techniques to stimulate discrete cortical or subcortical brain regions with therapeutic purposes in otherwise intractable patients: for example, thousands of advanced Parkinsonian patients, as well as patients with tremor or dystonia, benefited by deep brain stimulation (DBS) procedures (neural targets: basal ganglia nuclei). A new era for DBS is currently opening for patients with drug-resistant depression, obsessive-compulsive disorders, severe epilepsy, migraine and chronic pain (neural targets: basal ganglia and other subcortical nuclei or associative fibres). Vagal nerve stimulation (VNS) has shown clinical benefits in patients with pharmacoresistant epilepsy and depression. Non-invasive brain stimulation neuromodulatory techniques such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are also being increasingly investigated for their therapeutic potential in several neurological and psychiatric disorders. In this review, we first address the most common neural targets of each of the mentioned brain stimulation techniques, and the known mechanisms of their neuromodulatory action on stimulated brain networks. Then, we discuss how DBS, VNS, rTMS and tDCS could impact on the function of brainstem centres controlling vital functions, critically reviewing their acute and long-term effects on brain sympathetic outflow controlling heart function and blood pressure. Finally, as there is clear experimental evidence in animals that brain stimulation can affect autonomic and heart functions, we will try to give a critical perspective on how it may enhance our understanding of the cortical/subcortical mechanisms of autonomic cardiovascular regulation, and also if it might find a place among therapeutic opportunities in patients with otherwise intractable autonomic dysfunctions.

The Influence of Vagus Nerve and Spinal Cord Stimulation on the Ictal Fast Ripple Activity in a Spike-and-Wave Rat Model of Seizures

OBJECTIVES

Fast ripple (FR) activity has received increasing attention as a potential epileptic marker. The current knowledge on how neurostimulation affects FRs is, however, very limited. In this study, we assess the influence of the vagus nerve stimulation (VNS) and spinal cord stimulation (SCS) frequency on ictal FRs associated with spike-and-wave (SW) seizures.

METHODS

SW discharges were induced and maintained by an infusion of pentylenetetrazol in rat. During ongoing SW seizures, SCS was conducted at 30, 80, 130, and 180 Hz and VNS at 10, 30, 80, 130, and 180 Hz. The FRs were derived from intracortical recordings and the FR rate was used for quantifying the level of FR activity.

RESULTS

The FR rate was significantly correlated (r = 0.81) with the level of total pentylenetetrazol dose. Compared with no stimulation intervals, SCS conducted at 80, 130, and 180 Hz significantly reduced the normalized FR rate by 24, 38, and 44%, respectively. Similarly, VNS conducted at 30, 80, 130, and 180 Hz significantly reduced the normalized FR rate by 23, 40, 61, and 65%, respectively.

CONCLUSIONS

In the present model of sustained SW seizures, the FR rate was proportional with the severity of the SW seizures. Both SCS and VNS attenuated the FR rate and this attenuation was consistently strongest at the higher stimulation frequencies. Our results suggest that SCS may induce some of the same antiepileptic effects as VNS.

Vagus nerve stimulation for the treatment of refractory epilepsy

Vagus nerve stimulation (VNS) represents one of the main surgical options for the treatment of the refractory epilepsy in pediatric and adult patients. There are several mechanism involved in vagal nerve stimulation which could influence the pathophysiology of seizures like neuromodulation of the thalamic and subthalamic nuclei involved in seizure initiation and the modulation of the neurotransmitters pattern norepinefrin, GABA, and serotonin. The VNS system is composed of the implanted components (the generator, the lead with the electrodes attached) and the programming system components (programming wand and handheld computer). The authors present their experience with 81 patients diagnosed with refractory epilepsy, investigated, selected and implanted with vagal neurostimulators between December 2012 and January 2015 in Neurosurgery Clinic, "Bagdasar-Arseni" Emergency Hospital. The surgical technique and the potential pitfalls are described in detail. There were 20 children (24,7%) and 61 (75,3%) adults in this series. There was no death in this series and no intraoperative incidence. One patient presented dysphagia postoperatively which completely remitted after two months of follow-up. The outcome in term of seizure frequency and severity was better for patients under 30 years compared with patients older than 30 years. VNS represents now a safe, quick and efficient surgical procedure with a minimum period of hospitalization and a short recovery period. The good results on long term improve the quality of life of the patients and facilitate the social and professional reinsertion

Effects of responsive electrical brain stimulation on intracranial electroencephalogram spikes

OBJECTIVES

Responsive cortical electrical stimulation with implanted devices is under investigation for seizures. While designed to terminate seizures, might this stimulation also affect the underlying epileptic process of seizure generation?

MATERIALS AND METHODS

Four patients undergoing intracranial electroencephalogram (EEG) for seizure localization had an external responsive neurostimulator (eRNS) connected to their seizure-onset zones. The eRNS detected interictal EEG spikes and stimulated at the focus. We quantified spikes at three locations: (1) near stimulation, (2) remote but in the same lobe as stimulation, and (3) in different lobe from stimulation. Ten-minute windows were analyzed at three times: (1) baseline, (2) after the first four hours of stimulation, and (3) poststimulation. One blinded investigator performed manual spike counts. Quantitative measures were total spikes, spike-free intervals (continuous ten-sec segments with no spikes), and spike clusters (one-sec intervals with three or more spikes).

RESULTS

Some changes in spikes occurred in each patient, but no uniform pattern emerged. Two general observations were made: (1) spike counts within a given patient exhibited internally consistent changes with stimulation; (2) across patients, the nature of spike count changes varied, indicating patient-to-patient variability. For example, poststimulation, two patients had more and two patients had fewer total spikes. However, when spikes decreased near stimulation, they decreased at other sites, and when spikes increased near stimulation, they increased at other sites.

CONCLUSIONS

Changes in spike occurrence, organization, and topography with stimulation suggest the eRNS affected spike generation and may affect the underlying interictal epileptic process. Case-to-case variability may be due to individual patient factors, and its significance is yet to be determined.

Sphenopalatine ganglion neuromodulation in migraine: what is the rationale?

OBJECTIVE

The objective of this article is to review the prospect of treating migraine with sphenopalatine ganglion (SPG) neurostimulation.

BACKGROUND

Fuelled by preliminary studies showing a beneficial effect in cluster headache patients, the potential of treating migraine with neurostimulation has gained increasing interest within recent years, as current treatment strategies often fail to provide adequate relief from this debilitating headache. Common migraine symptoms include lacrimation, nasal congestion, and conjunctival injection, all parasympathetic manifestations. In addition, studies have suggested that parasympathetic activity may also contribute to the pain of migraineurs. The SPG is the largest extracranial parasympathetic ganglion of the head, innervating the meninges, lacrimal gland, nasal mucosa, and conjunctiva, all structures involved in migraine with cephalic autonomic symptoms.

CONCLUSION

We propose two possible mechanisms of action: 1) interrupting the post-ganglionic parasympathetic outflow to inhibit the pain and cephalic autonomic symptoms, and 2) modulating the sensory processing in the trigeminal nucleus caudalis. To further explore SPG stimulation in migraineurs as regards therapeutic potential and mode of action, randomized clinical trials are warranted.

Non-pharmacological treatment options for refractory epilepsy: an overview of human treatment modalities and their potential utility in dogs

Refractory epilepsy is a common disorder both in humans and dogs and treatment protocols are difficult to optimise. In humans, different non-pharmacological treatment modalities currently available include surgery, the ketogenic diet and neurostimulation. Surgery leads to freedom from seizures in 50-75% of patients, but requires strict patient selection. The ketogenic diet is indicated in severe childhood epilepsies, but efficacy is limited and long-term compliance can be problematic. In the past decade, various types of neurostimulation have emerged as promising treatment modalities for humans with refractory epilepsy. Currently, none of these treatment options are used in routine daily clinical practice to treat dogs with the condition. Since many dogs with poorly controlled seizures do not survive, the search for alternative treatment options for canine refractory epilepsy should be prioritised. This review provides an overview of non-pharmacological treatment options for human refractory epilepsy. The current knowledge and limitations of these treatments in canine refractory epilepsy is also discussed.

Vagus nerve stimulation to augment recovery from severe traumatic brain injury impeding consciousness: a prospective pilot clinical trial

OBJECTIVES

Traumatic brain injury (TBI) has high morbidity and mortality in both civilian and military populations. Blast and other mechanisms of TBI damage the brain by causing neurons to disconnect and atrophy. Such traumatic axonal injury can lead to persistent vegetative and minimally conscious states (VS and MCS), for which limited treatment options exist, including physical, occupational, speech, and cognitive therapies. More than 60 000 patients have received vagus nerve stimulation (VNS) for epilepsy and depression. In addition to decreased seizure frequency and severity, patients report enhanced mood, reduced daytime sleepiness independent of seizure control, increased slow wave sleep, and improved cognition, memory, and quality of life. Early stimulation of the vagus nerve accelerates the rate and extent of behavioral and cognitive recovery after fluid percussion brain injury in rats.

METHODS

We recently obtained Food and Drug Administration (FDA) approval for a pilot prospective randomized crossover trial to demonstrate objective improvement in clinical outcome by placement of a vagus nerve stimulator in patients who are recovering from severe TBI. Our hypothesis is that stimulation of the vagus nerve results in increased cerebral blood flow and metabolism in the forebrain, thalamus, and reticular formation, which promotes arousal and improved consciousness, thereby improving outcome after TBI resulting in MCS or VS.

DISCUSSION

If this study demonstrates that VNS can safely and positively impact outcome, then a larger randomized prospective crossover trial will be proposed.

Modulation of cortical synchrony by vagus nerve stimulation in adult rats

Vagus nerve stimulation (VNS) is a palliative treatment for intractable epilepsy. Therapeutic mechanisms of VNS have not been elucidated. In this study, we measured the local field potential (LFP) with high-spatial resolution using a microelectrode array in adult rats, and analyzed VNS-evoked phase modulation at a local network level. Eight adult Wistar rats (270 - 330 g) were used. Each rat underwent implantation of VNS system (Cyberonics, Houston, TX., USA) under 1.5% isoflurane anesthesia. One week after implantation, right temporal craniotomy was performed under the same as previous anesthesia. Subsequently, a microelectrode array was placed in the temporal lobe cortex, and LFP was recorded with sampling rate of 1000 Hz. Phase-locking value (PLV) between all pairs of electrodes in varied frequency bands was calculated in order to evaluate the effect of VNS in terms of synchrony of neuronal activities. PLV was calculated both in a normal state and in an epileptic state induced by kainic acid. VNS increased PLV in a normal state, particularly in high-γ band. In an epileptic state, VNS increased PLV in high-γ band, and decreased in d and low-β bands. VNS modulates synchrony in a band-specific and state-dependent manner. VNS might keep cortical synchrony within the optimal state.

Efficacy of vagus nerve stimulation in posttraumatic versus nontraumatic epilepsy

OBJECT

In the US, approximately 500,000 individuals are hospitalized yearly for traumatic brain injury (TBI), and posttraumatic epilepsy (PTE) is a common sequela of TBI. Improved treatment strategies for PTE are critically needed, as patients with the disorder are often resistant to antiepileptic medications and are poor candidates for definitive resection. Vagus nerve stimulation (VNS) is an adjunctive treatment for medically refractory epilepsy that results in a ≥ 50% reduction in seizure frequency in approximately 50% of patients after 1 year of therapy. The role of VNS in PTE has been poorly studied. The aim of this study was to determine whether patients with PTE attain more favorable seizure outcomes than individuals with nontraumatic epilepsy etiologies.

METHODS

Using a case-control study design, the authors retrospectively compared seizure outcomes after VNS therapy in patients with PTE versus those with nontraumatic epilepsy (non-PTE) who were part of a large prospectively collected patient registry.

RESULTS

After VNS therapy, patients with PTE demonstrated a greater reduction in seizure frequency (50% fewer seizures at the 3-month follow-up; 73% fewer seizures at 24 months) than patients with non-PTE (46% fewer seizures at 3 months; 57% fewer seizures at 24 months). Overall, patients with PTE had a 78% rate of clinical response to VNS therapy at 24 months (that is, ≥ 50% reduction in seizure frequency) as compared with a 61% response rate among patients with non-PTE (OR 1.32, 95% CI 1.07-1.61), leading to improved outcomes according to the Engel classification (p < 0.0001, Cochran-Mantel-Haenszel statistic).

CONCLUSIONS

Vagus nerve stimulation should be considered in patients with medically refractory PTE who are not good candidates for resection. A controlled prospective trial is necessary to further examine seizure outcomes as well as neuropsychological outcomes after VNS therapy in patients with intractable PTE.

Efficacy of vagus nerve stimulation for epilepsy by patient age, epilepsy duration, and seizure type

Medically refractory epilepsy is a morbid condition, and many patients are poor candidates for surgical resection because of multifocal seizure origin or eloquence near epileptic foci. Vagus nerve stimulation (VNS) was approved in 1997 by the US Food and Drug Administration as an adjunctive treatment of intractable epilepsy for individuals aged 12 years and more with partial epilepsy. Controversy persists regarding the efficacy of VNS for epilepsy and about which patient populations respond best to therapy. In this article, the authors retrospectively studied a patient outcome registry and report the largest, to their knowledge, analysis of VNS outcomes in epilepsy.

Is there a role for vagus nerve stimulation therapy as a treatment of traumatic brain injury?

This paper aims to review the current literature on vagus nerve stimulation (VNS) use in animal models of traumatic brain injury (TBI) and explore its potential role in treatment of human TBI. A MEDLINE search yielded four primary papers from the same group that demonstrated VNS mediated improvement following fluid percussion models of TBI in rats, seen as motor and cognitive improvements, reduction of cortical oedema and neuroprotective effects. The underlying mechanisms are elusive and authors attribute these to attenuation of post traumatic seizures, a noradrenergic mechanism and as yet undetermined mechanisms. Reviewing and elaborating on these ideas, we speculate other potential mechanisms including attenuation of peri-infarct depolarisations, attenuation of glutamate mediated excitotoxicity, stabilisation of intracranial pressure, enhancement of synaptic plasticity, upregulation of endogenous neurogenesis and anti-inflammatory effects may have a role. Although this data unequivocally shows that VNS improves outcome from TBI in animal models, it remains to be determined if these findings translate clinically. Further studies are warranted.

Brain stimulation for the treatment of epilepsy

The treatment of patients with refractory epilepsy has always been challenging. Despite the availability of multiple antiepileptic medications and surgical procedures with which to resect seizure foci, there is a subset of epilepsy patients for whom little can be done. Currently available treatment options for these unfortunate patients include vagus nerve stimulation, the ketogenic diet, and electric stimulation, both direct and indirect, of brain nuclei thought to be involved in epileptogenesis. Studies of electrical stimulation of the brain in epilepsy treatment date back to the early 20th century, beginning with research on cerebellar stimulation. The number of potential targets has increased over the years to include the hippocampus, subthalamic nucleus, caudate nucleus, centromedian nucleus, and anterior nucleus of the thalamus (ANT). Recently the results of a large randomized controlled trial, the electrical Stimulation of the Anterior Nucleus of Thalamus for Epilepsy (SANTE) trial, were published, demonstrating a significant reduction in mean seizure frequency with ANT stimulation. Soon after, in 2011, the results of a second randomized, controlled trial—the NeuroPace RNS trial—were published. The RNS trial examined closed-loop, responsive cortical stimulation of seizure foci in patients with refractory partial epilepsy, again finding significant reduction in seizure frequency. In the present review, the authors examine the modern history of electrical stimulation of the brain for the treatment of epilepsy and discuss the results of 2 important, recently published trials, the SANTE and RNS trials.

Effects of amygdala-hippocampal stimulation on interictal epileptic discharges

Deep brain stimulation (DBS) of different nuclei is being evaluated as a treatment for epilepsy. While encouraging results have been reported, the effects of changes in stimulation parameters have been poorly studied. Here the effects of changes of pulse waveform in high frequency DBS (130 Hz) of the amygdala-hippocampal complex (AH) are presented. These effects were studied on interictal epileptic discharge rates (IEDRs). AH-DBS was implemented with biphasic versus pseudo monophasic charge balanced pulses, in two groups of patients: six with temporal lobe epilepsy (TLE) associated with hippocampal sclerosis (HS) and six with non lesional (NLES) temporal epilepsy. In patients with HS, IEDRs were significantly reduced with AH-DBS applied with biphasic pulses in comparison with monophasic pulse. IEDRs were significantly reduced in only two patients with NLES independently to stimulus waveform. Comparison to long-term seizure outcome suggests that IEDRs could be used as a neurophysiological marker of chronic AH-DBS and they suggest that the waveform of the electrical stimuli can play a major role in DBS. We concluded that biphasic stimuli are more efficient than pseudo monophasic pulses in AH-DBS in patients with HS. In patients with NLES epilepsy, other parameters relevant for efficacy of DBS remain to be determined.

Neurostimulation: vagus nerve stimulation and beyond

Patients with medically intractable epilepsy who are not candidates for epilepsy surgery could benefit from neurostimulation. At this time, vagus nerve stimulation (VNS) therapy is the only Food and Drug Administation-approved neurostimulation modality; it has been shown to be efficacious and just as well tolerated in children and adolescents as in adults. Notwithstanding the initial cost of the device and implantation, VNS therapy has been shown to be a cost-effective treatment, reducing direct medical costs and improving health-related quality of life measures. Deep brain stimulation of various brain regions, especially the anterior nucleus of the thalamus and responsive neurostimulation, also appear effective but are not yet approved for clinical use. Repetitive transcranial magnetic stimulation, which is also in early clinical development, is promising and could become available in the not too distant future.

Vagus nerve stimulation for epilepsy: a meta-analysis of efficacy and predictors of response

Vagus nerve stimulation (VNS) was approved by the US FDA in 1997 as an adjunctive treatment for medically refractory epilepsy. It is considered for use in patients who are poor candidates for resection or those in whom resection has failed. However, disagreement regarding the utility of VNS in epilepsy continues because of the variability in benefit reported across clinical studies. Moreover, although VNS was approved only for adults and adolescents with partial epilepsy, its efficacy in children and in patients with generalized epilepsy remains unclear. The authors performed the first meta-analysis of VNS efficacy in epilepsy, identifying 74 clinical studies with 3321 patients suffering from intractable epilepsy. These studies included 3 blinded, randomized controlled trials (Class I evidence); 2 nonblinded, randomized controlled trials (Class II evidence); 10 prospective studies (Class III evidence); and numerous retrospective studies. After VNS, seizure frequency was reduced by an average of 45%, with a 36% reduction in seizures at 3-12 months after surgery and a 51% reduction after > 1 year of therapy. At the last follow-up, seizures were reduced by 50% or more in approximately 50% of the patients, and VNS predicted a ≥ 50% reduction in seizures with a main effects OR of 1.83 (95% CI 1.80-1.86). Patients with generalized epilepsy and children benefited significantly from VNS despite their exclusion from initial approval of the device. Furthermore, posttraumatic epilepsy and tuberous sclerosis were positive predictors of a favorable outcome. In conclusion, VNS is an effective and relatively safe adjunctive therapy in patients with medically refractory epilepsy not amenable to resection. However, it is important to recognize that complete seizure freedom is rarely achieved using VNS and that a quarter of patients do not receive any benefit from therapy.

A novel implantable vagus nerve stimulation system (ADNS-300) for combined stimulation and recording of the vagus nerve: pilot trial at Ghent University Hospital

PURPOSE

Vagus nerve stimulation (VNS) is an established treatment for refractory epilepsy. The ADNS-300 is a new system for VNS that includes a rechargeable stimulus generator and an electrode for combined stimulation and recording. In this feasibility study, three patients were implanted with ADNS-300 for therapeutic VNS. In addition, compound action potentials (CAPs) were recorded to evaluate activation of the vagus nerve in response to VNS.

METHODS

Three patients were implanted with a cuff-electrode around the left vagus nerve, that was connected to a rechargeable pulse generator under the left clavicula. Two weeks after surgery, therapeutic VNS (0.25-1.25 mA, 500 μs, 30s on, 10 min off and 30Hz) was initiated and stimulus-induced CAPs were recorded.

RESULTS

The ADNS-300 system was successfully implanted in all three patients and patients were appropriately stimulated during six months of follow-up. A reduction in seizure frequency was demonstrated in two patients (43% and 40% in patients 1 and 3, respectively), while in patient 2 seizure frequency remained unchanged. CAPs could be recorded in patients 1 and 2, proving stimulation-induced activation of the vagus nerve.

CONCLUSION

This feasibility study demonstrates that the ADNS-300 system can be used for combined therapeutic stimulation (in 3/3 patients) and recording of CAPs in response to VNS (in 2/3 patients) up to three weeks after surgery. Implantation in a larger number of patients will lead to a better understanding of the electrophysiology of the vagus nerve, which in turn could result in more adequate and individualized VNS parameter choice.