Correlation between GABA(A) receptor density and vagus nerve stimulation in individuals with drug-resistant partial epilepsy

Age-related phenotype and biomarker changes in SSADH deficiency

Objective

Succinic Semialdehyde Dehydrogenase (SSADH) deficiency is a disorder of elevated gamma‐amino butyric acid (GABA) and gamma hydroxybutyric acid (GHB) and a complex neuropsychiatric profile. Adult reports suggest worsening epilepsy and high SUDEP risk.

Methods

Subjects with confirmed SSADH deficiency were recruited into a longitudinal study. Plasma thyroid hormone and total GABA/GHB were quantified by standard clinical chemistry methodologies and mass spectrometry, respectively.

Results

A total of 133 subjects with SSADH deficiency are enrolled in the registry; 49 participated in the longitudinal study. The age range of the population is 8 weeks to 63 years (median 7.75 year; 44% male). There is a significant difference in proportions among the age groups in subjects affected with hypotonia, compulsive behavior, sleep disturbances, and seizures. Epilepsy is present in 50% of the total population, and more prevalent in subjects 12 years and older (P = 0.001). The median age of onset for absence seizures was 2 years, and 12 years for generalized tonic‐clonic seizures (P < 0.01). The SUDEP rate in adults was 12% (4/33). There was a significant age‐dependent negative correlation between GABA and T₃ levels.

Interpretation

There is an age‐dependent association with worsening of epilepsy, behavioral disturbances including obsessive‐compulsive behavior, and sleep disturbances with age in SSADH deficiency. There is a high risk of SUDEP. We have observed more absence seizures in younger patients, compared to tonic‐clonic in the older cohort, which correlates with age‐related changes in GABA and GHB concentration and thyroid function, as well as the natural history of seizures in the murine model.

BOLD fMRI effects of transcutaneous vagus nerve stimulation in patients with chronic tinnitus

Objective

Vagus nerve stimulation (VNS) is a neuromodulation method used for treatment of epilepsy and depression. Transcutaneous VNS (tVNS) has been gaining popularity as a noninvasive alternative to VNS. Previous tVNS neuroimaging studies revealed brain (de)activation patterns that involved multiple areas implicated in tinnitus generation and perception. In this study, functional magnetic resonance imaging (fMRI) was used to explore the effects of tVNS on brain activity in patients with tinnitus.

Methods

Thirty-six patients with chronic tinnitus received tVNS to the inner tragus, cymba conchae, and earlobe (sham stimulation).

Results

The locus coeruleus and nucleus of the solitary tract in the brainstem were activated in response to stimulation of both locations compared with the sham stimulation. The cochlear nuclei were also activated, which was not observed in healthy subjects with normal hearing. Multiple auditory and limbic structures, as well as other brain areas associated with generation and perception of tinnitus, were deactivated by tVNS, particularly the parahippocampal gyrus, which was recently speculated to cause tinnitus in hearing-impaired patients.

Conclusions

tVNS via the inner tragus or cymba conchae suppressed neural activity in the auditory, limbic, and other tinnitus-related non-auditory areas through auditory and vagal ascending pathways in tinnitus patients. The results from this study are discussed in the context of several existing models of tinnitus. They indicate that the mechanism of action of tVNS might be involved in multiple brain areas responsible for the generation of tinnitus, tinnitus-related emotional annoyance, and their mutual reinforcement.

Transcutaneous Vagus Nerve Stimulation (tVNS) Enhances Response Selection During Sequential Action

Transcutaneous vagus nerve stimulation (tVNS) is a non-invasive and safe technique that transiently enhances brain GABA and noradrenaline levels. Although tVNS has been used mainly to treat clinical disorders such as epilepsy, recent studies indicate it is also an effective tool to investigate and potentially enhance the neuromodulation of action control. Given the key roles of GABA and noradrenaline in neural plasticity and cortical excitability, we investigated whether tVNS, through a presumed increase in level of these neurotransmitters, modulates sequential behavior in terms of response selection and sequence learning components. To this end we assessed the effect of single-session tVNS in healthy young adults (N = 40) on performance on a serial reaction time task, using a single-blind, sham-controlled between-subject design. Active as compared to sham tVNS did not differ in terms of acquisition of an embedded response sequence and in terms of performance under randomized response schedules. However, active tVNS did enhance response selection processes. Specifically, the group receiving active tVNS did not exhibit inhibition of return during response reversals (i.e., when trial N requires the same response as trial N-2, e.g., 1-2-1) on trials with an embedded response sequence. This finding indicates that tVNS enhances response selection processes when selection demands are particularly high. More generally, these results add to converging evidence that tVNS enhances action control performance.

Anatomo-Physiologic Basis for Auricular Stimulation

Introduction: Stimulation of cranial nerves modulates central nervous system (CNS) activity via the extensive connections of their brainstem nuclei to higher-order structures. Clinical experience with vagus-nerve stimulation (VNS) demonstrates that it produces robust therapeutic effects, however, posing concerns related to its invasiveness and side-effects. Discussion: Trigeminal nerve stimulation (TNS) has been recently proposed as a valid alternative to VNS. The ear presents afferent vagus and trigeminal-nerve distribution; its innervation is the theoretical basis of different reflex therapies, including auriculotherapy. An increasing number of studies have shown that several therapeutic effects induced by invasive VNS and TNS, can be reproduced by noninvasive auricular-nerve stimulation. However, the sites and neurobiologic mechanisms by which VNS and TNS produce their therapeutic effects are not clear yet. Conclusions: Accumulating evidence suggests that VNS and TNS share multiple levels and mechanisms of action in the CNS.

Transcutaneous vagus nerve stimulation (tVNS) enhances divergent thinking

Creativity is one of the most important cognitive skills in our complex and fast-changing world. Previous correlative evidence showed that gamma-aminobutyric acid (GABA) is involved in divergent but not convergent thinking. In the current study, a placebo/sham-controlled, randomized between-group design was used to test a causal relation between vagus nerve and creativity. We employed transcutaneous vagus nerve stimulation (tVNS), a novel non-invasive brain stimulation technique to stimulate afferent fibers of the vagus nerve and speculated to increase GABA levels, in 80 healthy young volunteers. Creative performance was assessed in terms of divergent thinking (Alternate Uses Task) and convergent thinking tasks (Remote Associates Test, Creative Problem Solving Task, Idea Selection Task). Results demonstrate active tVNS, compared to sham stimulation, enhanced divergent thinking. Bayesian analysis reported the data to be inconclusive regarding a possible effect of tVNS on convergent thinking. Therefore, our findings corroborate the idea that the vagus nerve is causally involved in creative performance. Even thought we did not directly measure GABA levels, our results suggest that GABA (likely to be increased in active tVNS condition) supports the ability to select among competing options in high selection demand (divergent thinking) but not in low selection demand (convergent thinking).

Insufficient efficacy of vagus nerve stimulation for epileptic spasms and tonic spasms in children with refractory epilepsy

BACKGROUND

Vagus nerve stimulation (VNS) leads to palliation of refractory seizures. Epileptic spasms (ES) and tonic spasms (TS) appear in children with West syndrome and symptomatic generalized epilepsy. Both types of spasms are often characterized by truncal muscular contractions and ictal electroencephalography (EEG) findings comprising the contiguous phases: phase 1) 15-20 Hz, spindle-like fast activity (occur in 70%), 2) diffuse polyphasic δ/θ waves (100%), and 3) electrodecremental activity (70%). Here, we examined the effect of VNS on these spasms that are uniformly associated with the EEG and electromyogram changes.

METHODS

A consecutive series of 32 patients satisfied the inclusion criteria consisting of 1) medically refractory epilepsy, 2) VNS implantation between 2010 and 2015, 3) implantation of VNS before the age of 20 years, and 4) follow-up >2 years. From this cohort, 16 patients had spasms (ES/TS group), whereas the remaining 16 had partial seizures with or without secondary generalization (PS/SG group). We compared seizure outcomes between the two groups, and also determined the factors predicting these outcomes within the ES/TS group.

RESULTS

The outcomes after 2 years of implantation, defined using the McHugh classification, were as follows: II (for 2 patients), III (5), and V (9) in the ES/TS group; and I (3 patients), II (6), III (2), IV (1), and V (4) in the PS/SG group. The ES/TS group had significantly worse outcomes than the PS/SG group (p = 0.024, Mann-Whitney U test). Multivariate ordinal logistic regression analysis revealed that shorter mean durations of ictal events were associated with better seizure outcomes following VNS implantation (p = 0.007).

SIGNIFICANCE

Only 13% of the patients in the ES/TS group had seizure reductions of greater than 50%. VNS was less effective for the treatment of patients with ES/TS than for those with PS/SG and those described in previous studies.

Mesoscopic neuron population modeling of normal/epileptic brain dynamics

Simulations of EEG data provide the understanding of how the limbic system exhibits normal and abnormal states of the electrical activity of the brain. While brain activity exhibits a type of homeostasis of excitatory and inhibitory mesoscopic neuron behavior, abnormal neural firings found in the seizure state exhibits brain instability due to runaway oscillatory entrained neural behavior. We utilize a model of mesoscopic brain activity, the KIV model, where each network represents the areas of the limbic system, i.e., hippocampus, sensory cortex, and the amygdala. Our model initially demonstrates oscillatory entrained neural behavior as the epileptogenesis, and then by increasing the external weights that join the three networks that represent the areas of the limbic system, seizure activity entrains the entire system. By introducing an external signal into the model, simulating external electrical titration therapy, the modeled seizure behavior can be 'rebalanced' back to its normal state.

Pairing sound with vagus nerve stimulation modulates cortical synchrony and phase coherence in tinnitus: An exploratory retrospective study

Recent research has shown that vagus nerve stimulation (VNS) paired with tones or with rehabilitative training can help patients to achieve reductions in tinnitus perception or to expedite motor rehabilitation after suffering an ischemic stroke. The rationale behind this treatment is that VNS paired with experience can drive neural plasticity in a controlled and therapeutic direction. Since previous studies observed that gamma activity in the auditory cortex is correlated with tinnitus loudness, we assessed resting-state source-localized EEG before and after one to three months of VNS-tone pairing in chronic tinnitus patients. VNS-tone pairing reduced gamma band activity in left auditory cortex. VNS-tone pairing also reduced the phase coherence between the auditory cortex and areas associated with tinnitus distress, including the cingulate cortex. These results support the hypothesis that VNS-tone pairing can direct therapeutic neural plasticity. Targeted plasticity therapy might also be adapted to treat other conditions characterized by hypersynchronous neural activity.

Supplementation of gamma-aminobutyric acid (GABA) affects temporal, but not spatial visual attention

In a randomized, double-blind, and placebo-controlled experiment, the acute effects of gamma-aminobutyric acid (GABA) supplementation on temporal and spatial attention in young healthy adults were investigated. A hybrid two-target rapid serial visual presentation task was used to measure temporal attention and integration. Additionally, a visual search task was used to measure the speed and accuracy of spatial attention. While temporal attention depends primarily on the distribution of limited attentional resources across time, spatial attention represents the engagement and disengagement by relevant and irrelevant stimuli across the visual field. Although spatial attention was unaffected by GABA supplementation altogether, we found evidence supporting improved performance in the temporal attention task. The attentional blink was numerically, albeit not significantly, attenuated at Lag 3, and significantly fewer order errors were committed at Lag 1, compared to the placebo condition. No effect was found on temporal integration rates. Although there is controversy about whether oral GABA can cross the blood-brain barrier, our results offer preliminary evidence that GABA intake might help to distribute limited attentional resources more efficiently, and can specifically improve the identification and ordering of visual events that occur in close temporal succession.

Transcutaneous vagus nerve stimulation (tVNS) modulates flow experience

Flow has been defined as a pleasant psychological state that people experience when completely absorbed in an activity. Previous correlative evidence showed that the vagal tone (as indexed by heart rate variability) is a reliable marker of flow. So far, it has not yet been demonstrated that the vagus nerve plays a causal role in flow. To explore this we used transcutaneous vagus nerve stimulation (tVNS), a novel non-invasive brain stimulation technique that increases activation of the locus coeruleus (LC) and norepinephrine release. A sham/placebo-controlled, randomized cross-over within-subject design was employed to infer a causal relation between the stimulated vagus nerve and flow as measured using the Flow Short-Scale in 32 healthy young volunteers. In both sessions, while being stimulated, participants had to rate their flow experience after having performed a task for 30 min. Active tVNS, compared to sham stimulation, decreased flow (as indexed by absorption scores). The results can be explained by the network reset theory, which assumes that high-phasic LC activity promotes a global reset of attention over exploitation of the current focus of attention, allowing rapid behavioral adaptation and resulting in decreased absorption scores. Furthermore, our findings corroborate the hypothesis that the vagus nerve and noradrenergic system are causally involved in flow.

Novel Therapeutic Targets Against Spreading Depression

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

The Vagus Nerve in Appetite Regulation, Mood, and Intestinal Inflammation

Although the gastrointestinal tract contains intrinsic neural plexuses that allow a significant degree of independent control over gastrointestinal functions, the central nervous system provides extrinsic neural inputs that modulate, regulate, and integrate these functions. In particular, the vagus nerve provides the parasympathetic innervation to the gastrointestinal tract, coordinating the complex interactions between central and peripheral neural control mechanisms. This review discusses the physiological roles of the afferent (sensory) and motor (efferent) vagus in regulation of appetite, mood, and the immune system, as well as the pathophysiological outcomes of vagus nerve dysfunction resulting in obesity, mood disorders, and inflammation. The therapeutic potential of vagus nerve modulation to attenuate or reverse these pathophysiological outcomes and restore autonomic homeostasis is also discussed.

Vagus Nerve Stimulation and Other Neuromodulation Methods for Treatment of Traumatic Brain Injury

The objective of this paper is to review the current literature regarding the use of vagus nerve stimulation (VNS) in preclinical models of traumatic brain injury (TBI) as well as discuss the potential role of VNS along with alternative neuromodulation approaches in the treatment of human TBI. Data from previous studies have demonstrated VNS-mediated improvement following TBI in animal models. In these cases, VNS was observed to enhance motor and cognitive recovery, attenuate cerebral edema and inflammation, reduce blood brain barrier breakdown, and confer neuroprotective effects. Yet, the underlying mechanisms by which VNS enhances recovery following TBI remain to be fully elucidated. Several hypotheses have been offered including: a noradrenergic mechanism, reduction in post-TBI seizures and hyper-excitability, anti-inflammatory effects, attenuation of blood-brain barrier breakdown, and cerebral edema. We present other potential mechanisms by which VNS acts including enhancement of synaptic plasticity and recruitment of endogenous neural stem cells, stabilization of intracranial pressure, and interaction with the ghrelin system. In addition, alternative methods for the treatment of TBI including deep brain stimulation, transcranial magnetic stimulation, transcranial direct current stimulation, and focused ultrasound stimulation are discussed. Although the primary source data show that VNS improves TBI outcomes, it remains to be determined if these findings can be translated to clinical settings.

Vagus nerve stimulation inhibits cortical spreading depression

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

Vagus nerve stimulation therapy in partial epilepsy: a review

Epilepsy is a chronic neurological disorder characterized by recurrent, unprovoked epileptic seizures. The majority of people given a diagnosis of epilepsy have a good prognosis, but 20-30 % will develop drug-resistant epilepsy. Vagus nerve stimulation (VNS) is a neuromodulatory treatment that is used as an adjunctive therapy for treating people with medically refractory epilepsy. It consists of chronic intermittent electrical stimulation of the vagus nerve, delivered by a programmable pulse generator (Neuro-Cybernetic Prosthesis). In 1997, the Food and Drug Administration approved VNS as adjunctive treatment for medically refractory partial-onset seizures in adults and adolescents. This article reviews the literature from 1988 to nowadays. We discuss thoroughly the anatomy and physiology of vagus nerve and the potential mechanisms of actions and clinical applications involved in VNS therapy, as well as the management, safety, tolerability and effectiveness of VNS therapy. VNS for partial seizures appears to be an effective and well tolerated treatment in adult and pediatric patients. People noted improvements in feelings of well-being, alertness, memory and thinking skills, as well as mood. The adverse effect profile is substantially different from the adverse effect profile associated with antiepileptic drugs, making VNS a potential alternative for patients with difficulty tolerating antiepileptic drug adverse effects. Despite the passing years and the advent of promising neuromodulation technologies, VNS remains an efficacy treatment for people with medically refractory epilepsy. Past and ongoing investigations in other indications have provided signals of the therapeutic potential in a wide variety of conditions.

Transcutaneous Vagus Nerve Stimulation Enhances Post-error Slowing

People tend to slow down after they commit an error, a phenomenon known as post-error slowing (PES). It has been proposed that slowing after negative feedback or unforeseen errors is linked to the activity of the locus coeruleus–norepinephrine (LC–NE) system, but there is little direct evidence for this hypothesis. Here, we assessed the causal role of the noradrenergic system in modulating PES by applying transcutaneous vagus nerve stimulation (tVNS), a new noninvasive and safe method to stimulate the vagus nerve and to increase NE concentrations in the brain. A single-blind, sham-controlled, between-group design was used to assess the effect of tVNS in healthy young volunteers (n = 40) during two cognitive tasks designed to measure PES. Results showed increased PES during active tVNS, as compared with sham stimulation. This effect was of similar magnitude for the two tasks. These findings provide evidence for an important role of the noradrenergic system in PES.

Transcutaneous trigeminal nerve stimulation induces a long-term depression-like plasticity of the human blink reflex

The beneficial effects of trigeminal nerve stimulation (TNS) on several neurological disorders are increasingly acknowledged. Hypothesized mechanisms include the modulation of excitability in networks involved by the disease, and its main site of action has been recently reported at brain stem level. Aim of this work was to test whether acute TNS modulates brain stem plasticity using the blink reflex (BR) as a model. The BR was recorded from 20 healthy volunteers before and after 20 min of cyclic transcutaneous TNS delivered bilaterally to the infraorbital nerve. Eleven subjects underwent sham-TNS administration and were compared to the real-TNS group. In 12 subjects, effects of unilateral TNS were tested. The areas of the R1 and R2 components of the BR were recorded before and after 0 (T0), 15 (T15), 30 (T30), and 45 (T45) min from TNS. In three subjects, T60 and T90 time points were also evaluated. Ipsi- and contralateral R2 areas were significantly suppressed after bilateral real-TNS at T15 (p = 0.013), T30 (p = 0.002), and T45 (p = 0.001), while R1 response appeared unaffected. The TNS-induced inhibitory effect on R2 responses lasted up to 60 min. Real- and sham-TNS protocols produced significantly different effects (p = 0.005), with sham-TNS being ineffective at any time point tested. Bilateral TNS was more effective (p = 0.009) than unilateral TNS. Acute TNS induced a bilateral long-lasting inhibition of the R2 component of the BR, which resembles a long-term depression-like effect, providing evidence of brain stem plasticity produced by transcutaneous TNS. These findings add new insight into mechanisms of TNS neuromodulation and into physiopathology of those neurological disorders where clinical benefits of TNS are recognized.

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.

RETRACTED: Transcutaneous vagus nerve stimulation (tVNS) enhances response selection during action cascading processes

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This retraction comes after a thorough and time-consuming analysis of the published article and the data it reports, following an investigation from the University of Leiden. On date 15th November 2021 European Neuropsychopharmacology received advice from University of Leiden, containing allegations of misconduct concerning the data reported in this article. Due to the nature of the concerns raised about this paper, the Editor-in-Chief examined all documents provided, all aspects of the peer review and editorial process and requested the view of each of the authors. The Editor-in-Chief wishes to acknowledge the co-operation of all parties. The Editor-in-Chief considers that there is a legitimate cause for concern regarding deletion of participants from datasets. The Editor-in-Chief commends the authors for their willingness in participating in this dialogue. However, given the concerns raised, the suggestion of the University of Leiden, and the view expressed by some of the authors, Retraction of this paper is inevitable. The Editor-in-Chief and the entire editorial board will use this case as a reminder to be as diligent as possible in the peer review process and to support transparency and openness in data sharing.

Vagus nerve stimulation for partial seizures

BACKGROUND

Vagus nerve stimulation (VNS) is a neuromodulatory treatment that is used as an adjunctive therapy for treating people with medically refractory epilepsy. VNS consists of chronic intermittent electrical stimulation of the vagus nerve, delivered by a programmable pulse generator. The majority of people given a diagnosis of epilepsy have a good prognosis, and their seizures will be controlled by treatment with a single antiepileptic drug (AED), but up to 20%-30% of patients will develop drug-resistant epilepsy, often requiring treatment with combinations of AEDs. The aim of this systematic review was to overview the current evidence for the efficacy and tolerability of vagus nerve stimulation when used as an adjunctive treatment for people with drug-resistant partial epilepsy. This is an updated version of a Cochrane review published in Issue 7, 2010.

OBJECTIVES

To determine:(1) The effects on seizures of VNS compared to controls e.g. high-level stimulation compared to low-level stimulation (presumed sub-therapeutic dose); and(2) The adverse effect profile of VNS compared to controls e.g. high-level stimulation compared to low-level stimulation.

SEARCH METHODS

We searched the Cochrane Epilepsy Group's Specialised Register (23 February 2015), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 23 February 2015), MEDLINE (1946 to 23 February 2015), SCOPUS (1823 to 23 February 2015), ClinicalTrials.gov (23 February 2015) and ICTRP (23 February 2015). No language restrictions were imposed.

SELECTION CRITERIA

The following study designs were eligible for inclusion: randomised, double-blind, parallel or crossover studies, controlled trials of VNS as add-on treatment comparing high and low stimulation paradigms (including three different stimulation paradigms - duty cycle: rapid, mid and slow) and VNS stimulation versus no stimulation or a different intervention. Eligible participants were adults or children with drug-resistant partial seizures not eligible for surgery or who failed surgery.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion and extracted data. The following outcomes were assessed: (a) 50% or greater reduction in total seizure frequency; (b) treatment withdrawal (any reason); (c) adverse effects; (d) quality of life; (e) cognition; (f) mood. Primary analyses were intention-to-treat. Sensitivity best and worst case analyses were also undertaken to account for missing outcome data. Pooled Risk Ratios (RR) with 95% confidence intervals (95% Cl) were estimated for the primary outcomes of seizure frequency and treatment withdrawal. For adverse effects, pooled RRs and 99% CI's were calculated.

MAIN RESULTS

Five trials recruited a total of 439 participants and between them compared different types of VNS stimulation therapy. Baseline phase ranged from 4 to 12 weeks and double-blind treatment phases from 12 to 20 weeks in the five trials. Overall, two studies were rated as having a low risk of bias and three had an unclear risk of bias due to lack of reported information around study design. Effective blinding of studies of VNS is difficult due to the frequency of stimulation-related side effects such as voice alteration; this may limit the validity of the observed treatment effects. Four trials compared high frequency stimulation to low frequency stimulation and were included in quantitative syntheses (meta-analyses).The overall risk ratio (95% CI) for 50% or greater reduction in seizure frequency across all studies was 1.73 (1.13 to 2.64) showing that high frequency VNS was over one and a half times more effective than low frequency VNS. For this outcome, we rated the evidence as being moderate in quality due to incomplete outcome data in one included study; however results did not vary substantially and remained statistically significant for both the best and worst case scenarios. The risk ratio (RR) for treatment withdrawal was 2.56 (0.51 to 12.71), however evidence for this outcome was rated as low quality due to imprecision of the result and incomplete outcome data in one included study. The RR of adverse effects were as follows: (a) voice alteration and hoarseness 2.17 (99% CI 1.49 to 3.17); (b) cough 1.09 (99% CI 0.74 to 1.62); (c) dyspnea 2.45 (99% CI 1.07 to 5.60); (d) pain 1.01 (99% CI 0.60 to 1.68); (e) paresthesia 0.78 (99% CI 0.39 to 1.53); (f) nausea 0.89 (99% CI 0.42 to 1.90); (g) headache 0.90 (99% CI 0.48 to 1.69); evidence of adverse effects was rated as moderate to low quality due to imprecision of the result and/or incomplete outcome data in one included study. No important heterogeneity between studies was found for any of the outcomes.

AUTHORS' CONCLUSIONS

VNS for partial seizures appears to be an effective and well tolerated treatment in 439 included participants from five trials. Results of the overall efficacy analysis show that VNS stimulation using the high stimulation paradigm was significantly better than low stimulation in reducing frequency of seizures. Results for the outcome "withdrawal of allocated treatment" suggest that VNS is well tolerated as withdrawals were rare. No significant difference was found in withdrawal rates between the high and low stimulation groups, however limited information was available from the evidence included in this review so important differences between high and low stimulation cannot be excluded . Adverse effects associated with implantation and stimulation were primarily hoarseness, cough, dyspnea, pain, paresthesia, nausea and headache, with hoarseness and dyspnea more likely to occur on high stimulation than low stimulation. However, the evidence on these outcomes is limited and of moderate to low quality. Further high quality research is needed to fully evaluate the efficacy and tolerability of VNS for drug resistant partial seizures.

An overview of PET neuroimaging

Over the past 35 years or so, PET brain imaging has allowed powerful and unique insights into brain function under normal conditions and in disease states. Initially, as PET instrumentation continued to develop, studies were focused on brain perfusion and glucose metabolism. This permitted refinement of brain imaging for important, non-oncologic clinical indications. The ability of PET to not only provide spatial localization of metabolic changes but also to accurately and consistently quantify their distribution proved valuable for applications in the clinical setting. Specifically, glucose metabolism brain imaging using (F-18) fluorodeoxyglucose continues to be invaluable for evaluating patients with intractable seizures for identifying seizure foci and operative planning. Cerebral glucose metabolism also contributes to diagnosis of neurodegenerative diseases that cause dementia. Alzheimer disease, dementia with Lewy bodies, and the several variants of frontotemporal lobar degeneration have differing typical patterns of hypometabolism. In Alzheimer disease, hypometabolism has furthermore been associated with poorer cognitive performance and ensuing cognitive and functional decline. As the field of radiochemistry evolved, novel radioligands including radiolabeled flumazenil, dopamine transporter ligands, nicotine receptor ligands, and others have allowed for further understanding of molecular changes in the brain associated with various diseases. Recently, PET brain imaging reached another milestone with the approval of (F-18) florbetapir imaging by the United States Federal Drug Administration for detection of amyloid plaque accumulation in brain, the major histopathologic hallmark of Alzheimer disease, and efforts have been made to define the clinical role of this imaging agent in the setting of the currently limited treatment options. Hopefully, this represents the first of many new radiopharmaceuticals that would allow improved diagnostic and prognostic information in these and other clinical applications, including Parkinson disease and traumatic brain injury.

Noninvasive vagus nerve stimulation as treatment for trigeminal allodynia

Implanted vagus nerve stimulation (VNS) has been used to treat seizures and depression. In this study, we explored the mechanism of action of noninvasive vagus nerve stimulation (nVNS) for the treatment of trigeminal allodynia. Rats were repeatedly infused with inflammatory mediators directly onto the dura, which led to chronic trigeminal allodynia. Administration of nVNS for 2 minutes decreased periorbital sensitivity in rats with periorbital trigeminal allodynia for up to 3.5 hours after stimulation. Using microdialysis, we quantified levels of extracellular neurotransmitters in the trigeminal nucleus caudalis (TNC). Allodynic rats showed a 7.7±0.9-fold increase in extracellular glutamate in the TNC after i.p. administration of the chemical headache trigger glyceryl trinitrate (GTN; 0.1 mg/kg). Allodynic rats that received nVNS had only a 2.3±0.4-fold increase in extracellular glutamate after GTN, similar to the response in control naive rats. When nVNS was delayed until 120 minutes after GTN treatment, the high levels of glutamate in the TNC were reversed after nVNS. The nVNS stimulation parameters used in this study did not produce significant changes in blood pressure or heart rate. These data suggest that nVNS may be used to treat trigeminal allodynia.

Brain stimulation in the treatment of epilepsy

Stimulation of the brain for the treatment of epilepsy, indirectly via the vagus nerve and directly through intracranial targets, is feasible and has increased in use and complexity over the past 10 years. Vagus nerve stimulation is widely applied and the present indications and outcomes together with possible ways in which the treatment could be refined are reviewed. The application of stimulation to deep-brain targets is also reviewed along with present practice and results. Possible developments in the use of direct intracranial stimulation are also considered.

Neuroendocrine homeostasis after vagus nerve stimulation in rats

BACKGROUND

The vagus nerve is important in maintaining HPA axis and sympatho-adrenal system (SAS) homeostasis, however little is known about the effect of vagus nerve stimulation (VNS), as used therapeutically, on these functions. Accordingly, the effect of VNS on plasma indices of HPA axis (ACTH, corticosterone), and SAS (norepinephrine, epinephrine) function were evaluated in rats.

METHODS

Male rats, on day-0 (D0), underwent surgeries for implantation of catheters into the right jugular vein and programmable (VNP) or non-programmable (VND) neurocybernetic devices encircling the left cervical vagus. On D7, after a blood sample, the device in VNP rats was programmed to deliver 500 μs width, 0.25 mA current pulses at 20 Hz ('on' 30s, 'off' 5 min) followed by timed blood samples during the next 90 min. In acute studies, VNS was stopped at 60 min and the rats were perfused at 90 min to evaluate neuronal Fos immunoreactivity (Fos-IR). In chronic studies, the probe remained active. In these rats, the HPA axis response to airpuff-startle stressor (D17) and anterior pituitary CRF-receptor binding (D26) were evaluated.

RESULTS

During acute VNS, plasma indices of HPA axis and SAS activity, as well as Fos-IR activation pattern in brain regions known to increase after stress, were not different between VND and VNP rats. During chronic VNS, stress-induced HPA axis responses exhibited a tendency toward faster recovery to baseline in VNP rats.

CONCLUSIONS

Therapeutic VNS is not a stressor and does not compromise HPA axis or SAS homeostasis. Chronic VNS may facilitate development of efficient feedback mechanisms.

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.

The wonders of the Wanderer

Vagus is Latin for wandering, and the vagus nerve fully deserves this name due to its extensive distribution through the body. Indeed, one of the lines of the song that accompanied the 2012 G. L. Brown Prize Lecture exaggerates this diversity, 'My function's almost anythin', and vagus is my name'. Alteration of vagal activity was first investigated in the 1880s as a treatment for epilepsy, and vagus nerve stimulation is now an approved treatment for refractory epilepsy and depression in the USA, despite an incomplete understanding of the mechanisms involved. Vagus nerve stimulation could be beneficial in many other conditions, including heart failure, tinnitus, chronic hiccups, Alzheimer's disease and inflammatory diseases. Inhibition of vagal activity could also be beneficial in some conditions, e.g. reducing activation of vagal respiratory afferents to treat chronic cough. This review discusses evidence underlying some current and potential therapeutic applications of vagal modulation, illustrating the wonders of the Wanderer.

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 reduces infarct size in rat focal cerebral ischemia: an unlikely role for cerebral blood flow

We sought to investigate the effect of cervical vagus nerve stimulation (VNS) on cerebral blood flow (CBF), infarct volume, and clinical outcome in a model of middle cerebral artery occlusion in rats. Electrical stimulation of the right and left vagus nerves was initiated 30min after the induction of the right-sided ischemia and lasted for 1h. Infarct size measurement revealed that the volume of ischemic damage was 41-45% smaller in animals receiving stimulation as compared with control animals. Both the right and left VNS caused subtle reduction in CBF during each 30-s stimulation period that quickly returned back to the baseline level at the end of each stimulation cycle. There was no significant effect of VNS on CBF during the entire 1-h stimulation period. The effect of VNS on tissue outcome was associated with better neurological outcome at both 1- and 3-day time points after the induction of ischemia. These findings suggest that VNS-induced protection against acute ischemic brain injury is not primarily mediated by changes in CBF, stimulation of both the right and left nerve have comparable effects, and VNS is effective after ipsilateral and contralateral focal ischemia.

Epilepsy secondary to tuberous sclerosis: lessons learned and current challenges

BACKGROUND

In tuberous sclerosis complex (TSC), a substantially increased risk of developing epilepsy is present as a result of a disruption of a TSC gene expression in the brain and secondary abnormal cellular differentiation, migration, and proliferation. Dysregulated excitation probably has its roots in the disruption of GABAergic interneuron development. There is an age-dependent electroclinical expression of seizures, and epilepsy is often quite severe and unremitting.

DISCUSSION

The majority of patients (>60%) who are candidates for surgery remain seizure-free after tuberectomy. During the recent years technical advances in the localization of the epileptogenic zone during the recent years have lead to a 63% of Engel class I status after surgery compared with a previous 52%. In medically refractory patients not suitable for surgery, vagus nerve stimulation has proved efficacy in significantly reducing seizure frequency in more than 50% of cases. New evidence suggests that mTOR inhibitors may be helpful in the management of intractable epilepsy for individuals with TSC.

Vagus nerve stimulation for refractory epilepsy in tuberous sclerosis

The goal of the study was to assess the long-term seizure and neuropsychologic outcomes of patients with tuberous sclerosis and refractory epilepsy who received vagus nerve stimulator implantation. Eleven patients with a follow-up period of at least 12 months were studied retrospectively. The mean age at the time of implantation was 14 years (range, 2-35). Seizure outcome was rated as class I (>80% seizure frequency reduction) in 1 (9%), class II (50-79% reduction) in 7 (63%), and class III (<50% reduction) in 3 (27%). No patient experienced permanent adverse effects after the procedure. A significant increase of adaptive behaviors and quality of life was observed. Patients who had implantation during childhood exhibited a greater improvement in cognitive and neuropsychologic functioning. Vagus nerve stimulation can be considered an effective and safe therapeutic option in patients with tuberous sclerosis and refractory epilepsy who are not candidates for epilepsy surgery.

Defective cerebral gamma-aminobutyric acid-A receptor density in patients with systemic lupus erythematosus and central nervous system involvement. An observational study

Gamma-aminobutyric acid-A (GABA-A) receptors play a crucial role in regulating neuronal excitability and cognitive functions. Single-photon emission computerized tomography (SPECT) analysis of GABA-A receptors binding by 123I-labelled Iomazenil (123I-IMZ) has been applied in some neuropsychiatric disorders to investigate conditions where GABA-A receptor density can be detected in several pathophysiological conditions. In this study we investigate cerebral GABA-A receptor density in a small series of patients with systemic lupus erythematosus (SLE) and cognitive impairment characterized by recurrent, episodic memory loss. Nine female patients with SLE and cognitive alterations underwent to a clinical neuropsychiatric evaluation including digital video-EEG, brain MRI, 99mTc-ECD brain SPECT and 123I-IMZ brain SPECT. All patients tested showed diffuse or focal GABA-A receptor density reduction. This is, to our knowledge, the first report on GABA-A receptor density abnormalities associated with cognitive defects in SLE patients. We hypothesize that in our series a decrease in GABA-A receptor density might be related to the neurological manifestations. Further studies are needed to clarify this aspect and the possible mechanisms. GABA-A receptor density impairment might be due to the SLE-related cerebral vasculopathy, or to neuronal-reacting auto-antibodies or drugs which could interfere with GABA-A receptors expression/binding. This study may support the concept that cognitive impairment in systemic lupus erythematosus could be the outcome of fine-tuned neurotransmission alterations.

Modulation of seizure threshold by vagus nerve stimulation in an animal model for motor seizures

OBJECTIVE

The precise mechanism of action of vagus nerve stimulation (VNS) in suppressing epileptic seizures remains to be elucidated. This study investigates whether VNS modulates cortical excitability by determining the threshold for provoking focal motor seizures by cortical electrical stimulation before and after VNS.

MATERIAL AND METHODS

Male Wistar rats (n = 8) were implanted with a cuff-electrode around the left vagus nerve and with stimulation electrodes placed bilaterally on the rat motor cortex. Motor seizure threshold (MST) was assessed for each rat before and immediately after 1 h of VNS with standard stimulation parameters, during two to three sessions on different days.

RESULTS

An overall significant increase of the MST was observed following 1 h of VNS compared to the baseline value (1420 microA and 1072 microA, respectively; P < 0.01). The effect was reproducible over time with an increase in MST in each experimental session.

CONCLUSIONS

VNS significantly increases the MST in a cortical stimulation model for motor seizures. These data indicate that VNS is capable of modulating cortical excitability.