An update on noninvasive neuromodulation in the treatment of patients with prolonged disorders of consciousness

BACKGROUND

With the improvement of emergency techniques, the survival rate of patients with severe brain injury has increased. However, this has also led to an annual increase in the number of patients with prolonged disorders of consciousness (pDoC). Hence, recovery of consciousness is an important part of treatment. With advancing techniques, noninvasive neuromodulation seems a promising intervention. The objective of this review was to summarize the latest techniques and provide the basis for protocols of noninvasive neuromodulations in pDoC.

METHODS

This review summarized the advances in noninvasive neuromodulation in the treatment of pDoC in the last 5 years.

RESULTS

Variable techniques of neuromodulation are used in pDoC. Transcranial ultrasonic stimulation (TUS) and transcutaneous auricular vagus nerve stimulation (taVNS) are very new techniques, while transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) are still the hotspots in pDoC. Median nerve electrical stimulation (MNS) has received little attention in the last 5 years.

CONCLUSIONS

Noninvasive neuromodulation is a valuable and promising technique to treat pDoC. Further studies are needed to determine a unified stimulus protocol to achieve optimal effects as well as safety.

Neuromodulation techniques - From non-invasive brain stimulation to deep brain stimulation

Over the past 30 years, the field of neuromodulation has witnessed remarkable advancements. These developments encompass a spectrum of techniques, both non-invasive and invasive, that possess the ability to both probe and influence the central nervous system. In many cases neuromodulation therapies have been adopted into standard care treatments. Transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and transcranial ultrasound stimulation (TUS) are the most common non-invasive methods in use today. Deep brain stimulation (DBS), spinal cord stimulation (SCS), and vagus nerve stimulation (VNS), are leading surgical methods for neuromodulation. Ongoing active clinical trials using are uncovering novel applications and paradigms for these interventions.

The evolution of neuromodulation for chronic stroke: From neuroplasticity mechanisms to brain-computer interfaces

Stroke is one of the most common and debilitating neurological conditions worldwide. Those who survive experience motor, sensory, speech, vision, and/or cognitive deficits that severely limit remaining quality of life. While rehabilitation programs can help improve patients' symptoms, recovery is often limited, and patients frequently continue to experience impairments in functional status. In this review, invasive neuromodulation techniques to augment the effects of conventional rehabilitation methods are described, including vagus nerve stimulation (VNS), deep brain stimulation (DBS) and brain-computer interfaces (BCIs). In addition, the evidence base for each of these techniques, pivotal trials, and future directions are explored. Finally, emerging technologies such as functional near-infrared spectroscopy (fNIRS) and the shift to artificial intelligence-enabled implants and wearables are examined. While the field of implantable devices for chronic stroke recovery is still in a nascent stage, the data reviewed are suggestive of immense potential for reducing the impact and impairment from this globally prevalent disorder.

Vagus nerve stimulation during extinction learning reduces conditioned place preference and context-induced reinstatement of cocaine seeking

BACKGROUND

Drug use causes the formation of strong cue/reward associations which persist long after cessation of drug-taking and contribute to the long-term risk of relapse. Extinguishing these associations may reduce cue-induced craving and relapse. Previously, we found that pairing vagus nerve stimulation (VNS) with extinction of cocaine self-administration reduces cue-induced reinstatement; however, it remains unclear whether this was primarily caused by extinguishing the context, the instrumental response, or both.

OBJECTIVE

Hypothesis: We hypothesized that VNS can facilitate the extinction of both contextual cues and instrumental responding.

METHODS

Extinction of context was first tested using Pavlovian conditioned place preference (CPP). Next, the impact of VNS on the extinction of instrumental responding was assessed under ABA and AAA context conditions. In each extinction context separate groups of rats were either provided the opportunity to perform the instrumental response, or the levers were retracted for the duration of extinction training. Reinstatement was induced by reintroduction of the conditioned stimuli and/or the drug-paired context. Data were analyzed using one-way or two-way repeated measures ANOVAs.

RESULTS

VNS during extinction reduced reinstatement of CPP. VNS also reduced cue- and context-induced reinstatement of the instrumental response under both AAA and ABA conditions. The subjects' ability to engage with the lever during extinction was crucial for this effect. P values < 0.05 were considered significant.

CONCLUSIONS

Craving occurs in response to a range of conditioned stimuli and contexts; VNS may improve outcomes of behavioral therapy by facilitating extinction of both an instrumental response and/or contextual cues.

Pharmacoresistance - Epidemiology, mechanisms, and impact on epilepsy treatment

Understanding the natural history of and factors associated with pharmacoresistant epilepsy provides the foundation for formulating mechanistic hypotheses that can be evaluated to drive the development of novel treatments. This article reviews the modern definition of drug-resistant epilepsy, its prevalence and incidence, risk factors, hypothesized mechanisms, and the implication of recognizing pharmacoresistance in therapeutic strategies. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Vagus nerve stimulation (VNS) therapy update

Epilepsy affects millions of people worldwide. Approximately one-third have pharmacoresistant epilepsy, and of these, the majority are not candidates for epilepsy surgery. Vagus nerve stimulation (VNS) therapy has been an option to treat pharmacoresistant seizures for 30 years. In this update, we will review the clinical data that support the device's efficacy in children, adolescents, and adults. We will also review its side-effect profile, quality of life and cost benefits, and the impact the device has on sudden unexpected death in epilepsy (SUDEP). We will then discuss candidate selection and provide guidance on dosing and future models. Vagus nerve stimulation therapy is an effective treatment for many seizure types and epilepsy syndromes with a predictable and benign side-effect profile that supports its role as the most commonly prescribed device to treat pharmacoresistant epilepsy. "This article is part of the Supplement issue Neurostimulation for Epilepsy."

Non-invasive vagus nerve stimulation for the acute treatment of episodic and chronic cluster headache: A randomized, double-blind, sham-controlled ACT2 study

Background Clinical observations and results from recent studies support the use of non-invasive vagus nerve stimulation (nVNS) for treating cluster headache (CH) attacks. This study compared nVNS with a sham device for acute treatment in patients with episodic or chronic CH (eCH, cCH). Methods After completing a 1-week run-in period, subjects were randomly assigned (1:1) to receive nVNS or sham therapy during a 2-week double-blind period. The primary efficacy endpoint was the proportion of all treated attacks that achieved pain-free status within 15 minutes after treatment initiation, without rescue treatment. Results The Full Analysis Set comprised 48 nVNS-treated (14 eCH, 34 cCH) and 44 sham-treated (13 eCH, 31 cCH) subjects. For the primary endpoint, nVNS (14%) and sham (12%) treatments were not significantly different for the total cohort. In the eCH subgroup, nVNS (48%) was superior to sham (6%; p < 0.01). No significant differences between nVNS (5%) and sham (13%) were seen in the cCH subgroup. Conclusions Combing both eCH and cCH patients, nVNS was no different to sham. For the treatment of CH attacks, nVNS was superior to sham therapy in eCH but not in cCH. These results confirm and extend previous findings regarding the efficacy, safety, and tolerability of nVNS for the acute treatment of eCH.

A novel flexible cuff-like microelectrode for dual purpose, acute and chronic electrical interfacing with the mouse cervical vagus nerve

OBJECTIVE

Neural reflexes regulate immune responses and homeostasis. Advances in bioelectronic medicine indicate that electrical stimulation of the vagus nerve can be used to treat inflammatory disease, yet the understanding of neural signals that regulate inflammation is incomplete. Current interfaces with the vagus nerve do not permit effective chronic stimulation or recording in mouse models, which is vital to studying the molecular and neurophysiological mechanisms that control inflammation homeostasis in health and disease. We developed an implantable, dual purpose, multi-channel, flexible 'microelectrode' array, for recording and stimulation of the mouse vagus nerve.

APPROACH

The array was microfabricated on an 8 µm layer of highly biocompatible parylene configured with 16 sites. The microelectrode was evaluated by studying the recording and stimulation performance. Mice were chronically implanted with devices for up to 12 weeks.

MAIN RESULTS

Using the microelectrode in vivo, high fidelity signals were recorded during physiological challenges (e.g potassium chloride and interleukin-1β), and electrical stimulation of the vagus nerve produced the expected significant reduction of blood levels of tumor necrosis factor (TNF) in endotoxemia. Inflammatory cell infiltration at the microelectrode 12 weeks of implantation was limited according to radial distribution analysis of inflammatory cells.

SIGNIFICANCE

This novel device provides an important step towards a viable chronic interface for cervical vagus nerve stimulation and recording in mice.

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.

Chronic cyclic vagus nerve stimulation has beneficial electrophysiological effects on healthy hearts in the absence of autonomic imbalance

Cardiovascular disease degrades the regulatory function of the autonomic nervous system. Cyclic vagus nerve stimulation (VNS) is an already FDA-approved therapy for drug-resistant epilepsy and depression, and has been shown to normalize autonomic function and improve objective measures of heart function and subjective measures of heart failure symptoms. However, it remains unclear whether VNS may induce negative effects in patients with potentially healthy hearts where VNS can be used for epileptic patients. Hence, this study aims to investigate the effects of VNS on the hearts of healthy rats with normal autonomic balance. Sprague-Dawley rats were implanted with stimulators and randomized to either Sham or VNS groups. Rats in VNS group received 10 weeks of chronic intermittent VNS via stimulation of the right cervical vagus nerve. Echocardiography was performed at Baseline (prior to VNS), Week 2, and Week 9. After 10 weeks, high-resolution optical mapping was performed in ex vivo perfused hearts to evaluate the electrophysiological remodeling that occurs in the heart as a result of the VNS therapy. Chronic VNS modified the electrophysiological properties of healthy rat hearts by reducing the action potential duration at 50% (APD50) and 80% (APD80) repolarization. Chronic VNS also affected the restitution properties of the heart at the APD50 level and increased myocardial conduction velocity (CV). VNS did not induce any significant changes to ventricular ejection fraction (EF) and spatial dispersion of APD, thus indicating that VNS did not negatively affect cardiac function. VNS also reduced the susceptibility to ventricular arrhythmias (ventricular fibrillation [VF] and ventricular tachycardia [VT]) during ex vivo programmed electrical stimulation. In summary, chronic application of cyclic VNS induces changes to the electrophysiological properties of healthy rat hearts. The observed decrease in APD and increase in CV suggest that the beneficial effects of VNS do not require the presence of existing autonomic imbalance.

Theoretical Basis of Vagus Nerve Stimulation

Despite a myriad of medical and surgical treatments for epilepsy developed over the past few decades, a large subset of patients remains refractory to treatment. Over this time period, vagus nerve stimulation (VNS) has become an accepted and viable treatment modality for this population. Since the earliest report of VNS implantation in 1988, tens of thousands of patients worldwide have received VNS therapy, and >100,000 patient-years of experience have been accrued. The mechanisms underlying the response to VNS therapy continue to be elucidated. As understanding of the VNS mechanisms of action continues to grow, more pathologies will arise as potential treatment indications. Furthermore, current treatment populations with refractory epilepsy, depression, and inflammatory diseases may enjoy improved response to stimulation.

[Vagus nerve stimulation therapy for epilepsy]

Vagus nerve stimulation is a palliative treatment for medically intractable epilepsy. This treatment reduces the frequency and severity of seizures refractory to antiepileptic drugs. Implanted generator and helical electrodes electrically stimulate the left vagus nerve at the neck chronically and intermittently. This was the first electrostimulation therapy clinically introduced for epilepsy. This treatment approach is supported by randomized double-blind trials even though the anti-seizure effect of vagus nerve stimulation is palliative and not curative. In Western countries, particularly the United States, this therapy has become an important alternative treatment for a subpopulation of patients with drug-resistant seizures who are not good candidates for craniotomy. In Japan, vagus nerve stimulation therapy was finally approved in January 2010 and has been covered by public health insurance since July 2010. Here, the author reviews the history, efficacy, and safety of this treatment, surgical anatomy and physiology of the vagus nerve, and the putative mechanisms underlying inhibition of epileptic seizures and accompanying effect on the central nervous system. Further experimental and clinical studies regarding this treatment approach are required to elucidate the detailed mechanism of action, to clarify the predicting factors of favorable outcome, and to scientifically confirm the anti-seizure effect in children and in generalized seizures and the efficacy in improvement of cognitive function, development, and quality of life.

Vagus nerve stimulation (VNS): utility in neuropsychiatric disorders

Early in the last century, neuroscientists initially speculated that it might be possible to influence brain activity and associated behaviours by stimulating the vagus nerve in the neck. Several animal studies pointed to this possibility. In the 1980s, Zabara discovered that vagus nerve stimulation (VNS) could reduce or eliminate seizures in dogs. His discovery led to enhanced methods of direct VNS and the development of an implantable device for human VNS. VNS is now an accepted long-term treatment for epilepsy, used by over 15000 patients worldwide. Many have wondered whether VNS could treat other neuropsychiatric disorders. This paper reviews the neurobiology involved in VNS, highlights the VNS clinical findings to date, and discusses potential VNS research opportunities for both clinical and basic investigators. Comments on the clinical utility of VNS in actual clinical practice are provided.