Vagus nerve stimulation. A potential therapy for resistant depression?

Neuropsychiatric Lyme Disease and Vagus Nerve Stimulation

Lyme disease, the most common tick-borne disease in the United States, is caused by infection with the spirochete Borrelia burgdorferi. While most patients with acute Lyme disease recover completely if treated with antibiotics shortly after the onset of infection, approximately 10-30% experience post-treatment symptoms and 5-10% have residual symptoms with functional impairment (post-treatment Lyme disease syndrome or PTLDS). These patients typically experience pain, cognitive problems, and/or fatigue. This narrative review provides a broad overview of Lyme disease, focusing on neuropsychiatric manifestations and persistent symptoms. While the etiology of persistent symptoms remains incompletely understood, potential explanations include persistent infection, altered neural activation, and immune dysregulation. Widely recognized is that new treatment options are needed for people who have symptoms that persist despite prior antibiotic therapy. After a brief discussion of treatment approaches, the article focuses on vagus nerve stimulation (VNS), a neuromodulation approach that is FDA-approved for depression, epilepsy, and headache syndromes and has been reported to be helpful for other diseases characterized by inflammation and neural dysregulation. Transcutaneous VNS stimulates the external branch of the vagus nerve, is minimally invasive, and is well-tolerated in other conditions with few side effects. If well-controlled double-blinded studies demonstrate that transcutaneous auricular VNS helps patients with chronic syndromes such as persistent symptoms after Lyme disease, taVNS will be a welcome addition to the treatment options for these patients.

Neuromodulation Strategies to Reduce Inflammation and Improve Lung Complications in COVID-19 Patients

Since the outbreak of the COVID-19 pandemic, races across academia and industry have been initiated to identify and develop disease modifying or preventative therapeutic strategies has been initiated. The primary focus has been on pharmacological treatment of the immune and respiratory system and the development of a vaccine. The hyperinflammatory state (“cytokine storm”) observed in many cases of COVID-19 indicates a prognostically negative disease progression that may lead to respiratory distress, multiple organ failure, shock, and death. Many critically ill patients continue to be at risk for significant, long-lasting morbidity or mortality. The human immune and respiratory systems are heavily regulated by the central nervous system, and intervention in the signaling of these neural pathways may permit targeted therapeutic control of excessive inflammation and pulmonary bronchoconstriction. Several technologies, both invasive and non-invasive, are available and approved for clinical use, but have not been extensively studied in treatment of the cytokine storm in COVID-19 patients. This manuscript provides an overview of the role of the nervous system in inflammation and respiration, the current understanding of neuromodulatory techniques from preclinical and clinical studies and provides a rationale for testing non-invasive neuromodulation to modulate acute systemic inflammation and respiratory dysfunction caused by SARS-CoV-2 and potentially other pathogens. The authors of this manuscript have co-founded the International Consortium on Neuromodulation for COVID-19 to advocate for and support studies of these technologies in the current coronavirus pandemic.

Vagus nerve stimulation for conservative therapy-refractive epilepsy and depression

Numerous studies confirm that the vagus nerve stimulation (VNS) is an efficient, indirect neuromodulatory therapy with electrically induced current for epilepsy that cannot be treated by epilepsy surgery and is therapy-refractory and for drug therapy-refractory depression. VNS is an established, evidence-based and in the long-term cost-effective therapy in an interdisciplinary overall concept.Long-term data on the safety and tolerance of the method are available despite the heterogeneity of the patient populations. Stimulation-related side effects like hoarseness, paresthesia, cough or dyspnea depend on the stimulation strength and often decrease with continuing therapy duration in the following years. Stimulation-related side effects of VNS can be well influenced by modifying the stimulation parameters. Overall, the invasive vagus nerve stimulation may be considered as a safe and well-tolerated therapy option.For invasive and transcutaneous vagus nerve stimulation, antiepileptic and antidepressant as well as positive cognitive effects could be proven. In contrast to drugs, VNS has no negative effect on cognition. In many cases, an improvement of the quality of life is possible.iVNS therapy has a low probability of complete seizure-freedom in cases of focal and genetically generalized epilepsy. It must be considered as palliative therapy, which means that it does not lead to healing and requires the continuation of specific medication. The functional principle is a general reduction of the neuronal excitability. This effect is achieved by a slow increase of the effectiveness sometimes over several years. Responders are those patients who experience a 50% reduction of the seizure incidence. Some studies even reveal seizure-freedom in 20% of the cases. Currently, it is not possible to differentiate between potential responders and non-responders before therapy/implantation.The current technical developments of the iVNS generators of the new generation like closed-loop system (cardiac-based seizure detection, CBSD) reduce also the risk for SUDEP (sudden unexpected death in epilepsy patients), a very rare, lethal complication of epilepsies, beside the seizure severity.iVNS may deteriorate an existing sleep apnea syndrome and therefore requires possible therapy interruption during nighttime (day-night programming or magnet use) beside the close cooperation with sleep physicians.The evaluation of the numerous iVNS trials of the past two decades showed multiple positive effects on other immunological, cardiological, and gastroenterological diseases so that additional therapy indications may be expected depending on future study results. Currently, the vagus nerve stimulation is in the focus of research in the disciplines of psychology, immunology, cardiology as well as pain and plasticity research with the desired potential of future medical application.Beside invasive vagus nerve stimulation with implantation of an IPG and an electrode, also devices for transdermal and thus non-invasive vagus nerve stimulation have been developed during the last years. According to the data that are currently available, they are less effective with regard to the reduction of the seizure severity and duration in cases of therapy-refractory epilepsy and slightly less effective regarding the improvement of depression symptoms. In this context, studies are missing that confirm high evidence of effectiveness. The same is true for the other indications that have been mentioned like tinnitus, cephalgia, gastrointestinal complaints etc. Another disadvantage of transcutaneous vagus nerve stimulation is that the stimulators have to be applied actively by the patients and are not permanently active, in contrast to implanted iVNS therapy systems. So they are only intermittently active; furthermore, the therapy adherence is uncertain.

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.

A narrative review on invasive brain stimulation for treatment-resistant depression

While most patients with depression respond to pharmacotherapy and psychotherapy, about one-third will present treatment resistance to these interventions. For patients with treatment-resistant depression (TRD), invasive neurostimulation therapies such as vagus nerve stimulation, deep brain stimulation, and epidural cortical stimulation may be considered. We performed a narrative review of the published literature to identify papers discussing clinical studies with invasive neurostimulation therapies for TRD. After a database search and title and abstract screening, relevant English-language articles were analyzed. Vagus nerve stimulation, approved by the U.S. Food and Drug Administration as a TRD treatment, may take several months to show therapeutic benefits, and the average response rate varies from 15.2-83%. Deep brain stimulation studies have shown encouraging results, including rapid response rates (> 30%), despite conflicting findings from randomized controlled trials. Several brain regions, such as the subcallosal-cingulate gyrus, nucleus accumbens, ventral capsule/ventral striatum, anterior limb of the internal capsule, medial-forebrain bundle, lateral habenula, inferior-thalamic peduncle, and the bed-nucleus of the stria terminalis have been identified as key targets for TRD management. Epidural cortical stimulation, an invasive intervention with few reported cases, showed positive results (40-60% response), although more extensive trials are needed to confirm its potential in patients with TRD.

Effect of Long-Term Treatment with Vagus Nerve Stimulation on Mood and Quality of Life in Korean Patients with Drug-Resistant Epilepsy

BACKGROUND AND PURPOSE

This study aimed to determine the long-term effects of vagus nerve stimulation (VNS) treatment on suicidality, mood-related symptoms, and quality of life (QOL) in patients with drug-resistant epilepsy (DRE). We also investigated the relationships among these main effects, clinical characteristics, and VNS parameters.

METHODS

Among 35 epilepsy patients who underwent VNS implantation consecutively in our epilepsy center, 25 patients were recruited to this study for assessing the effects of VNS on suicidality, mood-related symptoms, and QOL. The differences in these variables between before and after VNS treatment were analyzed statistically using paired t-tests. Multiple linear regression analyses were also performed to determine how the patients' demographic and clinical characteristics influenced the variables that showed statistically significant changes after long-term VNS treatment.

RESULTS

After VNS, our patients showed significant improvements not only in the mean seizure frequency but also in suicidality, depression, and QOL. The reduction in depression was associated with the improvement in QOL and more-severe depression at baseline. The reduction in suicidality was associated with higher suicidality at baseline, smaller changes in depression, and less-severe depression at baseline. Improved QOL was associated with lower suicidality at baseline.

CONCLUSIONS

This study found that VNS decreased the mean seizure frequency in patients with DRE, and also improved their depression, suicidality, and QOL. These results provide further evidence for therapeutic effect of VNS on psychological comorbidities of patients with DRE.

Adjunctive Vagus Nerve Stimulation for Treatment-Resistant Depression: a Quantitative Analysis

Vagus nerve stimulation (VNS) has been increasingly studied in treating treatment-resistant depression (TRD), but the findings have been mixed. This updated meta-analysis was conducted to examine the efficacy and safety of adjunctive VNS for TRD. Controlled studies reporting on the efficacy and safety of adjunctive VNS for TRD were screened, identified and analyzed. Standardized mean difference (SMD), risk ratio (RR) and their 95% confidence intervals (CIs) were analyzed using RevMan version 5.3. Three controlled studies with a total of 1048 patients with TRD compared VNS (n = 622) with control (n = 426) groups. Only one study was rated as 'high quality' using the Jadad scale. Adjunctive VNS was significantly superior to the control group regarding study-defined response [SMD:1.96 (95%CI:1.60, 2.40), P < 0.00001, I² = 0%]. Patient-reported voice alteration occurred more frequently with adjunctive VNS for patients with TRD. No significant group differences were found regarding discontinuation due to any reason [RR:0.50 (95%CI:0.12, 2.09), P = 0.34, I² = 85%]. Adjunctive VNS appeared to be effective and relatively safe treatment for TRD. Further randomized controlled trials are needed to confirm the efficacy and safety of VNS for TRD.

Abdominal vagal deafferentation alters affective behaviors in rats

BACKGROUND

There is growing evidence for a role of abnormal gut-brain signaling in disorders involving altered mood and affect, including depression. Studies using vagus nerve stimulation (VNS) suggest that the disruption of vagal afferent signaling may contribute to these abnormalities. To test this hypothesis, we used a rat model of subdiaphragmatic vagal deafferentation (SDA), the most complete and selective vagal deafferentation method existing to date, to study the consequences of complete disconnection of abdominal vagal afferents on affective behaviors.

METHODS

SDA- and Sham-operated male rats were subjected to several tests that are commonly used in preclinical rodent models to assess the presence of anhedonic behavior, namely the novel object-induced exploration test, the novelty-suppressed eating test, and the sucrose preference test. In addition, we compared SDA and Sham rats in a social interaction test and the forced swim test to assess sociability and behavioral despair, respectively.

RESULTS

Compared to Sham controls, SDA rats consistently displayed signs of anhedonic behavior in all test settings used. SDA rats also showed increased immobility and reduced swimming in the forced swim test, whereas they did not differ from Sham controls with regards to social approach behavior.

LIMITATIONS

This study was conducted in male rats only. Hence, possible sex-specific effects of SDA on affective behaviors remained unexamined.

CONCLUSIONS

Our findings demonstrate that hedonic behavior and behavioral despair are subject to visceral modulation through abdominal vagal afferents. These data are compatible with preclinical models and clinical trials showing beneficial effects of VNS on depression-like and affective behaviors.

The role of maternal cardiac vagal control in the association between depressive symptoms and gestational hypertension

Reduced cardiac vagal control, indexed by relatively lower high-frequency heart rate variability (HF-HRV), is implicated in depressed mood and hypertensive disorders among non-pregnant adults whereas research in pregnancy is limited. This study examined whether maternal HF-HRV during pregnancy mediates the association between depressed mood and gestational hypertension. Depressive symptoms (Edinburgh Depression Scale) and HF-HRV were measured during early (M=14.9 weeks) and late (M=32.4 weeks) pregnancy in 287 women. Gestational hypertension was determined by chart review. Depressive symptoms were associated with less HF-HRV (b=-0.02, p=.001). There was an indirect effect of depressed mood on gestational hypertension through late pregnancy HF-HRV (b=0.04, 95% CI 0.0038, 0.1028) after accounting for heart rate. These findings suggest cardiac vagal control is a possible pathway through which prenatal depressed mood is associated with gestational hypertension, though causal ordering remains uncertain.

Non-pharmacological biological treatment approaches to difficult-to-treat depression

There has been substantial recent interest in novel brain stimulation treatments for difficult-to-treat depression. Electroconvulsive therapy (ECT) is a well established, effective treatment for severe depression. ECT's problematic side-effect profile and questions regarding optimal administration methods continue to be investigated. Magnetic seizure therapy, although very early in development, shows promise, with potentially similar efficacy to ECT but fewer side effects. Vagus nerve stimulation (VNS) and repetitive transcranial magnetic stimulation (rTMS) are clinically available in some countries. Limited research suggests VNS has potentially long-lasting antidepressant effects in a small group of patients. Considerable research supports the efficacy of rTMS. Both techniques require further study of optimal treatment parameters. Transcranial direct current stimulation may provide a low-cost antidepressant option if its efficacy is substantiated in larger samples. Deep brain stimulation is likely to remain reserved for patients with the most severe and difficult-to-treat depression, requiring further exploration of administration methods and its role in depression therapy. New and innovative forms of brain stimulation, including low-intensity ultrasound, low-field magnetic stimulation and epidural stimulation of the cortical surface, are in early stages of exploration and are yet to move into the clinical domain. Ongoing work is required to define which brain stimulation treatments are likely to be most useful, and in which patient groups. Clinical service development of brain stimulation treatments will likely be inconsistent and variable.

The role of electroconvulsive and neuromodulation therapies in the treatment of geriatric depression

Geriatric depression is associated with increased mortality because of suicide and decreases in functional and physical health. Many elders' depression is resistant to psychotherapy and medication and can become chronic. Electroconvulsive therapy (ECT) is increasingly used in the treatment of medication-resistant or life-threatening geriatric depression. Neuromodulation therapies (subconvulsive, focal, or subconvulsive and focal) are alternatives for the management of treatment-resistant depression in the elderly. Therapies that combine both strategies could be safer but may not be as effective as ECT. This review covers the evidence on the safety and efficacy of ECT and the neuromodulation therapies in geriatric depression.

The Promise of Heart Rate Variability Biofeedback: Evidence-Based Applications

Heart rate variability biofeedback has enjoyed increased popularity in recent years. In this review, empirical evidence from multiple sources is presented from the point of view of possible mechanisms of effect. While more research is clearly needed, the data thus far are certainly promising.

Neuromodulation therapies and treatment-resistant depression

Background

Patients with treatment-resistant depression (TRD) who showed partial response to pharmacological and psychotherapeutic interventions need a trial of neuromodulation therapies (NTs).

Objective

This paper aims to review evidence-based data on the use of NTs in TRD.

Method

Using keywords and combined-word strategy, multiple computer searches of PubMed, Google Scholar, Quertle(R), and Medline were conducted for retrieving relevant articles published in English-language peer-reviewed journals (2000–2012). Those papers that addressed NTs in TRD were retained for extensive review.

Results

Despite methodological challenges, a range of 30%–93% of TRD patients showed substantial improvement to one of the NTs. One hundred–percent improvement was reported in two single-case studies on deep brain stimulation. Some studies reported no benefits from transcranial direct current stimulation. NTs were reported to have good clinical efficacy, better safety margin, and benign side-effect profile. Data are limited regarding randomized clinical trials, long-term efficacy, and cost-effectiveness of these approaches. Both modified electroconvulsive therapy and magnetic seizure therapy were associated with reversible but disturbing neurocognitive adverse effects. Besides clinical utility, NTs including approaches on the horizon may unlock the biological basis underlying mood disorders including TRD.

Conclusion

NTs are promising in patients with TRD, as the majority of them show good clinical response measured by standardized depression scales. NTs need further technological refinements and optimization together with continuing well-designed studies that recruit larger numbers of participants with TRD.

Mortality and suicide risk in treatment-resistant depression: an observational study of the long-term impact of intervention

Major depressive disorder is a common global disease that causes a significant societal burden. Most interventional studies of depression provide a limited assessment of the interventions on mortality and suicide risks. This study utilizes data from an observational registry of patients with major depressive disorder to determine the impact of intervention (vagus nerve stimulation or standard pharmacological/non-pharmacological therapy) and a latent factor, patient trajectory toward response, on mortality, suicide and suicidal ideation. A total of 636 patients were available for an intent-to-treat analysis of all-cause mortality, suicide and suicidal ideation. Patients treated with vagus nerve stimulation in addition to standard therapies experienced lower, but not statistically significant, all-cause mortality (vagus nerve stimulation 4.93 per 1,000 person-years vs. 10.02 per 1,000 patient years for treatment as usual) and suicide rates (vagus nerve stimulation 0.88 per 1,000 person-years vs. 1.61 per 1,000 patient years for treatment as usual). Treatment with vagus nerve stimulation produced a statistically lower relative risk of suicidal ideation 0.80, 95% confidence interval (0.68,0.95). Further, patients that responded to either treatment saw a 51% reduction in relative risk of suicidal behavior; relative risk and 95% confidence interval of 0.49 (0.41,0.58). In summary, we find that treatment with adjunctive vagus nerve stimulation can potentially lower the risk of all-cause mortality, suicide and suicide attempts.

Brain stimulation therapies for psychiatric disorders: The first decade of the new millennium--A review

Three new brain stimulation therapies have emerged in the last decade for clinical use in psychiatric disorders. Combined with electroconvulsive therapy (ECT), these therapies offer much hope to patients with medication refractory depression, obsessive-compulsive disorder and auditory hallucinations of schizophrenia. In this article we briefly review the history, development and evidence for each of the four stimulation therapies and describe the current state-of-the-art. Neuromodulation is considered as a possible common mechanism mediating the effects of these therapies. Finally, empirical guidelines are suggested for the practicing psychiatrist for the optimal utilization of stimulation therapies. It is concluded that with increasing technological sophistication, research on optimal protocols and emergence of newer modalities of stimulation, the future holds much promise for neuromodulatory therapies in psychiatric disorders.

Vagus nerve stimulation has a positive effect on mood in patients with refractory epilepsy

BACKGROUND

Preliminary research on the efficacy of vagus nerve stimulation (VNS) indicated additional effects on neuropsychological variables like mood and quality of life (QOL).

OBJECTIVES

The objectives of this prospective longitudinal observational cohort study were to assess the effects of VNS on mood, QOL and cognition in patients with refractory epilepsy and to determine whether these effects occur dependent of seizure control.

METHODS

We included 41 patients with refractory epilepsy; treated with VNS as part of usual patient care. A neuropsychological battery was performed during baseline and repeated after 6 months of VNS in order to compare neuropsychological variables before and after VNS. All patients completed seizure diaries.

RESULTS

Significant improvements were observed for both mood and QOL after 6 months of VNS; based on the results in the POMS and QOLIE-89 questionnaires (p<0.05). There was no significant change in cognition. Mean percentage change in seizure frequency was -9.0%, while 20% of the patients achieved a seizure frequency reduction of 50% or more. No significant correlation was found between changes in seizure frequency and improvements in mood or QOL.

CONCLUSIONS

VNS is associated with improvements in both mood and QOL in patients with refractory epilepsy. Since these improvements appeared to be independent of seizure control, the results of this study indicate an additional antidepressant effect of VNS, which can be of extra value in view of the high co-morbidity of mood disturbances in patients with epilepsy.

The emerging use of brain stimulation treatments for psychiatric disorders

OBJECTIVE

The aim of this study was to review the current state of development and application of a wide range of brain stimulation approaches in the treatment of psychiatric disorders.

METHOD

The approaches reviewed include forms of minimally invasive magnetic and electrical stimulation, seizure induction, implanted devices and several highly novel approaches in early development.

RESULTS

An extensive range of brain stimulation approaches are now being widely used in the treatment of patients with psychiatric disorders, or actively investigated for this use. Both vagal nerve stimulation (VNS) and repetitive transcranial magnetic stimulation (rTMS) have been introduced into clinical practice in some countries. A small body of research suggests that VNS has some potentially long-lasting antidepressant effects in a minority of patients treated. rTMS has now been extensively investigated for over 15 years, with a large body of research now supporting its antidepressant effects. Further rTMS research needs to focus on defining the most appropriate stimulation methods and exploring its longer term use in maintenance protocols. Very early data suggest that magnetic seizure therapy (MST) has promise in the treatment of patients referred for electroconvulsive therapy: MST appears to have fewer side effects and may have similar efficacy. A number of other approaches including surgical and alternative forms of electrical stimulation appear to alter brain activity in a promising manner, but are in need of evaluation in more substantive patient samples.

CONCLUSIONS

It appears likely that the range of psychiatric treatments available for patients will grow over the coming years to progressively include a number of novel brain stimulation techniques.

Neuropsychologic effects of neuromodulation techniques for treatment-resistant depression: a review

Electroconvulsive therapy (ECT) and ablative neurosurgical procedures are established interventions for treatment-resistant depression (TRD), but their use may be limited in part by neuropsychological adverse effects. Additional neuromodulation strategies are being developed that aim to match or exceed the efficacy of ECT/ablative surgery with a better neurocognitive side effect profile. In this review, we briefly discuss the neurocognitive effects of ECT and ablative neurosurgical procedures, then synthesize the available neurocognitive information for emerging neuromodulation therapies, including repetitive transcranial magnetic stimulation, magnetic seizure therapy, transcranial direct current stimulation, vagus nerve stimulation, and deep brain stimulation. The available evidence suggests these procedures may be more cognitively benign relative to ECT or ablative neurosurgical procedures, though further research is clearly needed to fully evaluate the neurocognitive effects, both positive and negative, of these novel neuromodulation interventions.

Vagus nerve stimulation and emotional responses to food among depressed patients

BACKGROUND

Approved for treatment of treatment-resistant depression and for epilepsy, vagus nerve stimulation (VNS) therapy involves stimulation of the vagus nerve, affecting both mood and appetite regulating systems. VNS is associated with changes in food intake and weight loss in animals. Studies of its impact on food intake and weight with humans are limited. It is not known whether or how VNS influences emotional response to food, but vagus afferents project to regions in the insula involving satiety and taste.

METHOD

Thirty-three participants were recruited for three groups: depressed patients undergoing VNS therapy, depressed patients not undergoing VNS therapy, and healthy controls. All participants viewed images of foods twice in random order. When applicable, VNS devices were turned on for one viewing and off for the other. Participants were instructed to rate immediately after the viewings how each picture made them feel on a visual analog on three dimensions (unhappy to happy, calm to aroused, and small/submissive to big/domineering).

RESULTS

Controlling for time since last meal, a significant main effect was found for arousal ratings in response to sweet food images. Post-hoc analyses indicated that the VNS group demonstrated significant changes in arousal ratings between paired food image viewings compared to controls. Sixty-four percent of VNS participants demonstrated increases and 36% demonstrated decreases in arousal. Higher body mass indexes and greater levels of self-reported sweet cravings were associated with increased arousal during VNS activation.

CONCLUSIONS

This study was the first to examine the effects of acute left cervical VNS on emotional ratings of food in adults with major depression. Results suggest that VNS device activation may be associated with acute alteration in arousal response to sweet foods among depressed patients. Future research is needed to replicate these findings and to assess how activation of the vagus nerve affects eating and weight.

Chronic vagus nerve stimulation induces neuronal plasticity in the rat hippocampus

Vagus nerve stimulation (VNS) is used to treat pharmacotherapy-resistant epilepsy and depression. However, the mechanisms underlying the therapeutic efficacy of VNS remain unclear. We examined the effects of VNS on hippocampal neuronal plasticity and behaviour in rats. Cell proliferation in the hippocampus of rats subjected to acute (3 h) or chronic (1 month) VNS was examined by injection of bromodeoxyuridine (BrdU) and immunohistochemistry. Expression of doublecortin (DCX) and brain-derived neurotrophic factor (BDNF) was evaluated by immunofluorescence staining. The dendritic morphology of DCX+ neurons was measured by Sholl analysis. Our results show that acute VNS induced an increase in the number of BrdU+ cells in the dentate gyrus that was apparent 24 h and 3 wk after treatment. It also induced long-lasting increases in the amount of DCX immunoreactivity and in the number of DCX+ neurons. Neither the number of BrdU+ cells nor the amount of DCX immunoreactivity was increased 3 wk after the cessation of chronic VNS. Chronic VNS induced long-lasting increases in the amount of BDNF immunoreactivity and the number of BDNF+ cells as well as in the dendritic complexity of DCX+ neurons in the hippocampus. In contrast to chronic imipramine treatment, chronic VNS had no effect on the behaviour of rats in the forced swim or elevated plus-maze tests. Both chronic and acute VNS induced persistent changes in hippocampal neurons that may play a key role in the therapeutic efficacy of VNS. However, these changes were not associated with evident behavioural alterations characteristic of an antidepressant or anxiolytic action.

Optimization of vagus nerve stimulation parameters using the firing activity of serotonin neurons in the rat dorsal raphe

Vagus nerve stimulation (VNS) is a recently approved adjunctive intervention for treatment-resistant depression. This therapy enhances the firing rate of rat norepinephrine neurons after 1 h and that of serotonin (5-HT) neurons only after 14 days. Various stimulation parameters were thus tested on their capacity to enhance 5-HT neuronal firing because of the delayed action of VNS on the 5-HT system and its important role in the antidepressant response. Rats were implanted with a stimulator and treated for 14 days, each group of rats having only one stimulation parameter modified from the standard ones (0.25 mA, 20 Hz, 500 micros, 30 s ON/5 min OFF). Electrophysiological recordings showed that the usual parameters utilized in depressed patients, with the exception of current intensity, produced an optimal activation of 5-HT neurons. Excessive enhancement of the charge delivered to the nerve can lead to a loss of VNS effect on 5-HT neuronal firing.

Neurostimulatory therapeutics in management of treatment-resistant depression with focus on deep brain stimulation

Treatment-resistant depression continues to pose a major medical challenge, as up to one-third of patients with major depressive disorder fail to have an adequate response to standard pharmacotherapies. An improved understanding of the complex circuitry underlying depressive disorders has fostered an explosion in the development of new, nonpharmacological approaches. Each of these treatments seeks to restore normal brain activity via electrical or magnetic stimulation. In this article, the authors discuss the ongoing evolution of neurostimulatory treatments for treatment-resistant depression, reviewing the methods, efficacy, and current research on electroconvulsive therapy, repetitive transcranial magnetic stimulation, magnetic seizure therapy, focal electrically administered stimulated seizure therapy, transcranial direct current stimulation, chronic epidural cortical stimulation, and vagus nerve stimulation. Special attention is given to deep brain stimulation, the most focally targeted approach. The history, purported mechanisms of action, and current research are outlined in detail. Although deep brain stimulation is the most invasive of the neurostimulatory treatments developed to date, it may hold significant promise in alleviating symptoms and improving the quality of life for patients with the most severe and disabling mood disorders.

Brain stimulation techniques for the treatment of depression and other psychiatric disorders

OBJECTIVE

The aim of this paper was to review the development of repetitive transcranial magnetic stimulation (rTMS), magnetic seizure therapy (MST), vagal nerve stimulation (VNS), deep brain stimulation (DBS) and other recent brain stimulation techniques for their potential use in the treatment of a range of psychiatric disorders.

CONCLUSIONS

A considerable number of studies have been conducted to investigate the efficacy of rTMS. Although there are considerable problems with this research base, globally the studies suggest that rTMS has antidepressant efficacy. However, more research is required to define the most effective way of applying this technique. There is a much smaller research base supporting the use of VNS and to date the research suggests that only a minority of patients benefit from this procedure. Considerably more research is required in the use of the other techniques which at this stage have been tested only to a very small degree. It is likely that one, and possibly a number, of the new brain stimulation techniques will become available clinically in the psychiatric armamentarium in the coming years. However, considerable research is still required to establish efficacy and define the appropriate place in clinical practice for these treatment approaches.

Simulation study of stimulation parameters in desynchronisation based on the Hodgkin-Huxley small-world neural networks and its possible implications for vagus nerve stimulation

Adopting small-world neural networks of the Hodgkin-Huxley (HH) model, the stimulation parameters in desynchronisation and its possible implications for vagus nerve stimulation (VNS) are numerically investigated. With the synchronisation status of networks to represent epilepsy, then, adding pulse to stimulations to 10% of neurons to simulate the VNS, we obtain the desynchronisation status of networks (representing antiepileptic effects). The simulations show that synchronisation evolves into desynchronisation in the HH neural networks when a part (10%) of neurons are stimulated with a pulse current signal. The network desynchronisation appears to be sensitive to the stimulation parameters. For the case of the same stimulation intensity, weakly coupled networks reach desynchronisation more easily than strongly coupled networks. The network desynchronisation reduced by short-stimulation interval is more distinct than that of induced by long stimulation interval. We find that there exist the optimal stimulation interval and optimal stimulation intensity when the other stimulation parameters remain certain.

The use of repetitive transcranial magnetic stimulation and vagal nerve stimulation in the treatment of depression

PURPOSE OF REVIEW

Patients with depressive disorders often fail to respond to standard antidepressant medications and have few available treatment alternatives. Repetitive transcranial magnetic stimulation and vagal nerve stimulation have been developed and investigated over the last 10 years as potential treatment options for this and other psychiatric conditions. The aim of this paper is to review recent therapeutic trials of these techniques.

RECENT FINDINGS

Recent studies appear to have confirmed that standard left-sided repetitive transcranial magnetic stimulation has antidepressant efficacy, but that the degree of clinical effect may be somewhat limited. Promising data are emerging suggesting that other approaches, including right unilateral repetitive transcranial magnetic stimulation and sequential bilateral stimulation, may have equal or potentially greater effects. The evidence for the effectiveness of vagal nerve stimulation remains restricted to the primary company-sponsored trials. Although limited, these data suggest that valuable treatment effects may develop over time.

SUMMARY

Further repetitive transcranial magnetic stimulation research should actively investigate novel stimulation approaches before high-frequency left-sided stimulation is accepted as the standard approach. Given the invasive nature of vagal nerve stimulation and potential side effects, further research is urgently required. This should include the development of predictors of clinical response and definition of stimulation parameters with enhanced efficacy.

Vagus nerve stimulation: indications and limitations

Vagus nerve stimulation (VNS) is an established treatment for selected patients with medically refractory seizures. Recent studies suggest that VNS could be potentially useful in the treatment of resistant depressive disorder. Although a surgical procedure is required in order to implant the VNS device, the possibility of a long-term benefit largely free of severe side effects could give VNS a privileged place in the management of resistant depression. In addition, VNS appears to affect pain perception in depressed adults; a possible role of VNS in the treatment of severe refractory headache, intractable chronic migraine and cluster headache has also been suggested. VNS is currently investigated in clinical studies, as a potential treatment for essential tremor, cognitive deficits in Alzheimer's disease, anxiety disorders, and bulimia. Finally, other studies explore the potential use of VNS in the treatment of resistant obesity, addictions, sleep disorders, narcolepsy, coma and memory and learning deficits.

Selective unilateral autonomic activation: implications for psychiatry

Research advances have led to three methods for selectively activating one half of the autonomic nervous system in humans. The first method is an ancient yogic technique called unilateral forced nostril breathing (UFNB) that employs forced breathing through only one nostril while closing off the other. The second method works by stimulation of an autonomic reflex point on the fifth intercostal space near the axilla. The most recent method employs unilateral vagus nerve stimulation (VNS) via the mid-inferior cervical branch and requires surgical implantation of a wire and pacemaker. UFNB is non-invasive and seems to selectively activate the ipsilateral branch of the sympathetic nervous system with a possible compensation effect leading to contralateral VNS. UFNB and VNS have been employed to treat psychiatric disorders. While UFNB has been studied for its potential effects on the endogenous ultradian rhythms of the autonomic and central nervous system, and their tightly coupled correlates, VNS has yet to be studied in this regard. This article reviews these three methods and discusses their similarities, putative mechanisms, their studied effects on the endogenous autonomic nervous system and central nervous system rhythms, and their implications for the treatment of psychiatric disorders.

Vagus nerve stimulation for treatment-resistant depression: behavioral and neural effects on encoding negative material

OBJECTIVES

Vagus nerve stimulation (VNS) can improve depression. Cognitive models of depression highlight an over-representation of negative thoughts and memories, with depressed individuals showing memory facilitation for negative material. We hypothesized that the antidepressant action of VNS may emerge through corrective influences on 'negativity bias' in memory. We therefore examined the impact of VNS on emotional memory and its underlying brain activity.

METHODS

We tested a single patient undergoing VNS for treatment-resistant depression (TRD). Stimulation was set at a 30/66-second on/off cycle during three encoding blocks when the patient viewed randomly presented positive, negative, and neutral words. Following each block, VNS was switched off and the patient identified previously seen words from distractors in a subsequent recognition memory task. The patient was scanned using functional magnetic resonance imaging (fMRI) during the first encoding block.

RESULTS

There was robust recall of negative material viewed during 'off' cycles of VNS but subsequent memory of negative words was attenuated during active VNS ('on' cycles). VNS did not influence memory for neutral and positive words. With neuroimaging, direct modulatory effects of VNS were observed in dorsomedial, dorsolateral, and orbital regions of the prefrontal cortex. Moreover, during encoding of negative words, compared with positive and neutral words, VNS also modulated activity within orbitofrontal, ventromedial and polar prefrontal cortices, midcingulate cortex, and brain stem.

CONCLUSIONS

Our observations show that VNS can interfere with memory of negative information, an effect that may contribute to its antidepressant role. Neuroimaging implicated regions including the ventral and medial prefrontal cortex as an underlying neural substrate.

Vagus nerve stimulation (VNS) for depression: what do we know now and what should be done next?

Vagus nerve stimulation (VNS) therapy is the first US Food and Drug Administration-approved somatic clinical intervention for treatment-resistant depression (TRD). Long-term open data suggest a sustainable antidepressant response over time. Here we review the clinical data that exist so far and their limitations. We also discuss guidelines that may inform the clinical utilization of this procedure. Further clinical studies, in addition to prospective cost utilization and health economic investigations, are needed to better understand VNS therapy and the impact it holds on TRD care.

Increased extracellular concentrations of norepinephrine in cortex and hippocampus following vagus nerve stimulation in the rat

The vagus nerve is an important source of afferent information about visceral states and it provides input to the locus coeruleus (LC), the major source of norepinephrine (NE) in the brain. It has been suggested that the effects of electrical stimulation of the vagus nerve on learning and memory, mood, seizure suppression, and recovery of function following brain damage are mediated, in part, by the release of brain NE. The hypothesis that left vagus nerve stimulation (VNS) at the cervical level results in increased extracellular NE concentrations in the cortex and hippocampus was tested at four stimulus intensities: 0.0, 0.25, 0.5, and 1.0 mA. Stimulation at 0.0 and 0.25 mA had no effect on NE concentrations, while the 0.5 mA stimulation increased NE concentrations significantly in the hippocampus (23%), but not the cortex. However, 1.0 mA stimulation significantly increased NE concentrations in both the cortex (39%) and hippocampus (28%) bilaterally. The increases in NE were transient and confined to the stimulation periods. VNS did not alter NE concentrations in either structure during the inter-stimulation baseline periods. No differences were observed between NE levels in the initial baseline and the post-stimulation baselines. These findings support the hypothesis that VNS increases extracellular NE concentrations in both the hippocampus and cortex.

Cardiac vagal control in depression: a critical analysis

Rapidly developing research has found abnormal cardiac vagal control (CVC) in several physical and mental health conditions. CVC findings in depression are mixed, and the degree to which CVC is compromised in depression is unclear. A meta-analysis of 13 rigorous cross-sectional studies reveals that a diagnosis of depression exerts a small-to-medium effect size on CVC, and explains only about 2% of the overall variance in CVC. More robust data may emerge from alternative approaches to the depression-CVC relationship, such as the use of CVC to predict the course of the disorder. Despite the vigor of recent work on CVC and depression, overall findings are suggestive rather than conclusive. Methodological desiderata and priorities for future research are discussed, including the need to clarify the etiological significance of CVC.

VNS therapy in treatment-resistant depression: clinical evidence and putative neurobiological mechanisms

Currently available therapeutic interventions for treatment-resistant depression, including switch, combination, and augmentation strategies, are less than ideal. Observations of mood elevation during vagus nerve stimulation (VNS) therapy for pharmacoresistant epilepsy suggested a role for VNS therapy in refractory major depression and prompted clinical investigation of this neurostimulation modality. The VNS Therapy System has been available for treatment of pharmacoresistant epilepsy since 1997 and was approved by the US Food and Drug Administration for treatment-resistant depression in July, 2005. The physiology of the vagus nerve, mechanics of the VNS Therapy System, and efficacy and safety in pharmacoresistant epilepsy are reviewed. Promising results of VNS therapy for treatment-resistant depression have been forthcoming from both acute and long-term studies, evidenced in part by progressive improvements in depression rating scale scores during the 1st year of treatment with maintenance of response thereafter. VNS therapy is well tolerated in patients with either pharmacoresistant epilepsy or treatment-resistant depression. As in epilepsy, the mechanisms of VNS therapy of treatment-resistant depression are incompletely understood. However, evidence from neuroimaging and other studies suggests that VNS therapy acts via innervation of the nucleus tractus solitarius, with secondary projections to limbic and cortical structures that are involved in mood regulation, including brainstem regions that contain serotonergic (raphe nucleus) and noradrenergic (locus ceruleus) perikarya that project to the forebrain. Mechanisms that mediate the beneficial effects of VNS therapy for treatment-resistant depression remain obscure. Suggestions for future research directions are described.

A genetic approach for investigating vagal sensory roles in regulation of gastrointestinal function and food intake

Sensory innervation of the gastrointestinal (GI) tract by the vagus nerve plays important roles in regulation of GI function and feeding behavior. This innervation is composed of a large number of sensory pathways, each arising from a different population of sensory receptors. Progress in understanding the functions of these pathways has been impeded by their close association with vagal efferent, sympathetic, and enteric systems, which makes it difficult to selectively label or manipulate them. We suggest that a genetic approach may overcome these barriers. To illustrate the potential value of this strategy, as well as to gain insights into its application, investigations of CNS pathways and peripheral tissues involved in energy balance that benefited from the use of gene manipulations are reviewed. Next, our studies examining the feasibility of using mutations of developmental genes for manipulating individual vagal afferent pathways are reviewed. These experiments characterized mechanoreceptor morphology, density and distribution, and feeding patterns in four viable mutant mouse strains. In each strain a single population of vagal mechanoreceptors innervating the muscle wall of the GI tract was altered, and was associated with selective effects on feeding patterns, thus supporting the feasibility of this strategy. However, two limitations of this approach must be addressed for it to achieve its full potential. First, mutation effects in tissues outside the GI tract can contribute to changes in GI function or feeding. Additionally, knockouts of developmental genes are often lethal, preventing analysis of mature innervation and ingestive behavior. To address these issues, we propose to develop conditional gene knockouts restricted to specific GI tract tissues. Two genes of interest are brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), which are essential for vagal afferent development. Creating conditional knockouts of these genes requires knowledge of their GI tract expression during development, which little is known about. Preliminary investigation revealed that during development BDNF and NT-3 are each expressed in several GI tract regions, and that their expression patterns overlap in some tissues, but are distinct in others. Importantly, GI tissues that express BDNF or NT-3 are innervated by vagal afferents, and expression of these neurotrophins occurs during the periods of axon invasion and receptor formation, consistent with roles for BDNF or NT-3 in these processes and in receptor survival. These results provide a basis for targeting BDNF or NT-3 knockouts to specific GI tract tissues, and potentially altering vagal afferent innervation only in that tissue (e.g., smooth muscle vs. mucosa). Conditional BDNF or NT-3 knockouts that are successful in selectively altering a vagal GI afferent pathway will be valuable for developing an understanding of that pathway's roles in GI function and food intake.

Current and emerging somatic treatment strategies in psychotic major depression

Psychotic major depressive disorder (MDD) is a mood disorder characterized by severe affective and neurovegetative symptoms together with the presence of delusions and/or hallucinations. It is a common disorder seen in a quarter of consecutively admitted depressed patients and is often associated with severe symptomatology, increased suicide risk, poor acute response to antidepressants and poor acute and long-term treatment outcome. It is possible that poor response in psychotic depression is caused by the fact that we have yet to identify the most efficacious treatment protocol for psychotic MDD. Multiple studies have shown that modifications in the treatment paradigm may increase treatment efficacy in psychotic MDD. It has been generally accepted that, during the acute treatment phase, antidepressant-antipsychotic drug combination therapy is more effective than either treatment alone, although this strategy has recently been challenged. The question of the optimal duration of pharmacotherapy in order to prevent relapse and improve long-term (i.e., 5-year) outcome is a focus of current investigation. This article will review currently recommended treatment strategies for the acute, continuation and maintenance phases of therapy. In particular, it will address the role of newer-generation antidepressants, the role of second-generation antipsychotics, the use of mood stabilizers and indications for electroconvulsive therapy. Other possible treatment strategies such as transcranial magnetic stimulation, vagus nerve stimulation, deep-brain stimulation and glucocorticoid receptor antagonists will be discussed. Current recommendations for the prevention of relapse and improvement of long-term outcome will be reviewed.

Vagus nerve stimulation for treatment-resistant depression: a randomized, controlled acute phase trial

BACKGROUND

Vagus nerve stimulation (VNS) alters both concentrations of neurotransmitters or their metabolites and functional activity of central nervous system regions dysregulated in mood disorders. An open trial has suggested efficacy.

METHODS

This 10-week, acute, randomized, controlled, masked trial compared adjunctive VNS with sham treatment in 235 outpatients with nonpsychotic major depressive disorder (n = 210) or nonpsychotic, depressed phase, bipolar disorder (n = 25). In the current episode, participants had not responded adequately to between two and six research-qualified medication trials. A two-week, single-blind recovery period (no stimulation) and then 10 weeks of masked active or sham VNS followed implantation. Medications were kept stable. Primary efficacy outcome among 222 evaluable participants was based on response rates (>/=50% reduction from baseline on the 24-item Hamilton Rating Scale for Depression [HRSD(24)]).

RESULTS

At 10-weeks, HRSD(24) response rates were 15.2% for the active (n = 112) and 10.0% for the sham (n = 110) groups (p = .251, last observation carried forward [LOCF]). Response rates with a secondary outcome, the Inventory of Depressive Symptomatology - Self-Report (IDS-SR(30)), were 17.0% (active) and 7.3% (sham) (p = .032, LOCF). VNS was well tolerated; 1% (3/235) left the study because of adverse events.

CONCLUSIONS

This study did not yield definitive evidence of short-term efficacy for adjunctive VNS in treatment-resistant depression.

Stimulation of the vagus nerve attenuates macrophage activation by activating the Jak2-STAT3 signaling pathway

Acetylcholine released by efferent vagus nerves inhibits macrophage activation. Here we show that the anti-inflammatory action of nicotinic receptor activation in peritoneal macrophages was associated with activation of the transcription factor STAT3. STAT3 was phosphorylated by the tyrosine kinase Jak2 that was recruited to the alpha7 subunit of the nicotinic acetylcholine receptor. The anti-inflammatory effect of nicotine required the ability of phosphorylated STAT3 to bind and transactivate its DNA response elements. In a mouse model of intestinal manipulation, stimulation of the vagus nerve ameliorated surgery-induced inflammation and postoperative ileus by activating STAT3 in intestinal macrophages. We conclude that the vagal anti-inflammatory pathway acts by alpha7 subunit-mediated Jak2-STAT3 activation.

Recordings from the rat locus coeruleus during acute vagal nerve stimulation in the anaesthetised rat

Vagal nerve stimulation (VNS) is used as a treatment for Epilepsy and is currently under investigation as a treatment for depression (see [M.S. George, Z. Nahas, X. Li, F.A. Kozel, B. Anderson, K. Yamanaka, J.H. Chae, M.J. Foust, Novel treatments of mood disorders based on brain circuitry (ECT, MST, TMS, VNS, DBS), Semin. Clin. Neuropsychiatry 7 (2002) 293-304; M.S. George, A.J. Rush, H.A. Sackeim, L.B. Marangell, Vagus nerve stimulation (VNS): utility in neuropsychiatric disorders, Int. J. Neuropsychopharmacol. 6 (2003) 73-83] for reviews). The mechanism of action of VNS is not fully understood [E. Ben-Menachem, Vagus-nerve stimulation for the treatment of epilepsy, Lancet Neurol. 1 (2002) 477-482] despite numerous imaging investigations (see [E. Ben-Menachem, Vagus-nerve stimulation for the treatment of epilepsy, Lancet Neurol. 1 (2002) 477-482; M.S. George, Z. Nahas, X. Li, F.A. Kozel, B. Anderson, K. Yamanaka, J.H. Chae, M.J. Foust, Novel treatments of mood disorders based on brain circuitry (ECT, MST, TMS, VNS, DBS), Semin. Clin. Neuropsychiatry 7 (2002) 293-304; M.S. George, A.J. Rush, H.A. Sackeim, L.B. Marangell, Vagus nerve stimulation (VNS): utility in neuropsychiatric disorders, Int J Neuropsychopharmacol 6 (2003) 73-83; M.S. George, H.A. Sackeim, L.B. Marangell, M.M. Husain, Z. Nahas, S.H. Lisanby, J.C. Ballenger, A.J. Rush, Vagus nerve stimulation. A potential therapy for resistant depression? Psychiatr. Clin. North Am. 23 (2000) 757-783] for reviews). However, there is some evidence to suggest that the locus coeruleus may play a role modulating the effects of VNS. This study investigated the effects of VNS (0.3mA), of sufficient intensity to recruit the A and B fibre components of the vagus [D.M. Woodbury, J.W. Woodbury, Effects of vagal stimulation on experimentally induced seizures in rats, Epilepsia 31 (Suppl. 2) (1990) S7-S19], on the discharge rate of single neurons from the locus coeruleus. This study is the first to demonstrate a direct neuronal response from the locus coeruleus following acute challenge of VNS in the anaesthetised rat. The results of this study indicate that neuronal activity of the locus coeruleus is modulated by VNS. This pathway through the locus coeruleus may be significant for mediating the clinical effects of VNS.

Age effect on far field potentials from the brain stem after transcutaneous vagus nerve stimulation

Recently, a new electrophysiological method for the assessment of vagus nerve function in the brainstem has been proposed in healthy participants. Before this procedure may be applied to patients with neurodegenerative diseases, its feasibility in elderly healthy participants and a possible age effect on the measurement have to be investigated. The vagus sensory evoked potentials (VSEP) after transcutaneous electric stimulation of the sensory auricular branch of the vagus nerve have been assessed in healthy younger and elderly participants. VSEP measured as far field potentials probably originating in vagus nuclei in the brainstem were recorded in 20 of 22 younger as well as in 39 of 43 elderly healthy participants. Latencies were significantly longer in the elderly as compared to the younger participants, while no clear age effects on amplitudes were identified. These results indicate that the assessment of VSEP is feasible also in elderly healthy participants. This is a prerequisite for testing this method in elderly patients with neurodegenerative diseases like Alzheimer and Parkinson disease as a noninvasive tool to detect an affection of the brainstem nuclei of the vagus nerve early in their course.

Impairment of inhibitory control of the hypothalamic pituitary adrenocortical system in epilepsy

Excess comorbidity between depression and epilepsy proposes common pathophysiological patterns in both disorders. Neuroendocrine abnormalities were often observed in depression as well as in epilepsy. Lack of inhibitory control of the hypothalamic pituitary adrenocortical (HPA) system is a core feature of depression; main relay stations of this system are located in the amygdala and hippocampus, which are key regions for both disorders. Therefore we explored the feedback mechanism of the HPA system in epilepsy. In order to control for the impact of depression we focused on epilepsies without depression. We compared patients with epilepsy (subdivided by medication with or without hepatic enzyme inducing antiepileptic medication) with 16 healthy controls and 16 patients with unipolar major depression but without epilepsy. We observed a lack of inhibitory control of the HPA system in patients with epilepsy, also in the absence of enzyme inducing medication. An impact of the temporal lobe location of the epileptic focus could not be observed. Thus, epilepsies share with depression the deficiencies in the feedback mechanism of the HPA system, proposing common pathophysiological features of up to now unknown nature.

Acute vagus nerve stimulation using different pulse widths produces varying brain effects

BACKGROUND

Vagus nerve stimulation (VNS) is an approved treatment for epilepsy and has been investigated in clinical trials of depression. Little is known about the relationship of VNS parameters to brain function. Using the interleaved VNS /functional magnetic resonance imaging (fMRI) technique, we tested whether variations of VNS pulse width (PW) would produce different immediate brain activation in a manner consistent with single neuron PW studies.

METHODS

Twelve adult patients with major depression, treated with VNS, underwent three consecutive VNS/fMRI scans, each randomly using one of three PWs (130 micros, 250 micros, or 500 micros). The data were analyzed with SPM2.

RESULTS

Global activations induced by PWs 250 and 500 were both significantly greater than that induced by PW 130 but not significantly different from each other. For global deactivation, PWs 130 and 250 were both significantly greater than PW 500 but not significantly different from each other. Regional similarities and differences were also seen with the various PWs.

CONCLUSIONS

The data confirm our hypothesis that VNS at PW 500 globally produces no more activation than does PW 250, and PW 130 is insufficient for activation of some regions. These data suggest that PW is an important variable in producing VNS brain effects.

A review of functional neuroimaging studies of vagus nerve stimulation (VNS)

Vagus nerve stimulation (VNS) is a new method for preventing and treating seizures, and shows promise as a potential new antidepressant. The mechanisms of action of VNS are still unknown, although the afferent direct and secondary connections of the vagus nerve are well established and are the most likely route of VNS brain effects. Over the past several years, many groups have used functional brain imaging to better understand VNS effects on the brain. Since these studies differ somewhat in their methodologies, findings and conclusions, at first glance, this literature may appear inconsistent. Although disagreement exists regarding the specific locations and the direction of brain activation, the differences across studies are largely due to different methods, and the results are not entirely inconsistent. We provide an overview of these functional imaging studies of VNS. PET (positron emission tomography) and SPECT (single photon emission computed tomography) studies have implicated several brain areas affected by VNS, without being able to define the key structures consistently and immediately activated by VNS. BOLD (blood oxygen level dependent) fMRI (functional magnetic resonance imaging), with its relatively high spatio-temporal resolution, performed during VNS, can reveal the location and level of the brain's immediate response to VNS. As a whole, these studies demonstrate that VNS causes immediate and longer-term changes in brain regions with vagus innervations and which have been implicated in neuropsychiatric disorders. These include the thalamus, cerebellum, orbitofrontal cortex, limbic system, hypothalamus, and medulla. Functional neuroimaging studies have the potential to provide greater insight into the brain circuitry behind the activity of VNS.

Treatments for depression: wisdom imparted from treatments discarded

Many different forms of treatment have been used with patients suffering from depression. It can be difficult to examine current treatments and anticipate problems, mistakes, and limitations. However, a historical perspective allows an appreciation of the strengths and limitations of older treatments, and sheds light on current strategies. A variety of effective treatments have been discarded and forgotten. Important lessons can be learned by reviewing the history of treatments for depression. Many treatment strategies were based on accidental discovery, but nonetheless were found effective in reducing the symptoms of depression. Both case examples and group studies have documented the effectiveness of these older treatments. A review of discarded treatments reveals how a biological model can be limited in its ability to produce a lasting cure. Caution and skepticism are encouraged when innovative treatments are proposed.

The effect of electrical dental equipment on a vagus nerve stimulator's function

BACKGROUND

Dental patients who have epilepsy with pharmacologically refractory seizures may be treated with an implanted pulse generator that electrically stimulates the left vagus nerve. The pulse generator functions like a cardiac pacemaker. Some electrical dental devices have been shown to cause electromagnetic interference with the function of cardiac pacemakers. The potential effect of similar dental equipment on vagus nerve stimulators is unknown.

METHODS

Common electrical dental devices were operated at maximum power settings in close proximity to a representative vagus nerve stimulator. The author assessed any interference of the dental devices with the nerve stimulator function by observing oscilloscope tracings.

RESULTS

Under the conditions of this evaluation, none of the dental devices tested altered the function of the vagus nerve stimulator.

CONCLUSIONS

Some commonly used electrical dental devices may be used in close proximity to patients who have implanted vagus nerve stimulators without adverse effects on the nerve stimulator function.

CLINICAL IMPLICATIONS

Dentists and dental hygienists may encounter patients with implanted vagus nerve stimulators, and they need to be cognizant of developments in the treatment of epilepsy. Under the conditions of this study, use of common dental electrical devices did not alter the function of a vagus nerve stimulator. The findings of this study, however, should not be generalized to all types of electrical dental or medical devices, as a recent report indicates that treatment with diathermy devices is contraindicated for patients with implanted nerve stimulators.

Mechanisms and state of the art of vagus nerve stimulation

Vagus nerve stimulation (VNS) is an established treatment of medically refractory partial-onset seizures. Recent data from an open-label multicenter pilot study also suggest a potential clinical usefulness in the acute and maintenance treatment of drug-resistant depressive disorder. Despite the fact that surgery is needed to implant the stimulating device, the option of long-term use largely devoid of severe side effects would give this treatment modality a privileged place in the management of drug-resistant depression. However, definite therapeutic effects of clinical significance remain to be confirmed in large, placebo-controlled trials. Besides the potential clinical usefulness, VNS can be used as a research tool in epilepsy patients implanted for clinical reasons, allowing neurophysiologic investigations of the parasympathetic system and its interactions with other parts of the central nervous system.

Vagus nerve stimulation (VNS) synchronized BOLD fMRI suggests that VNS in depressed adults has frequency/dose dependent effects

Stimulation of the vagus nerve in the neck can reduce seizures in epilepsy patients, and may be helpful in treating depression. PET studies have shown that vagus nerve stimulation (VNS) in epilepsy patients causes acute dose (intensity) dependent changes in regional cerebral blood flow. We sought to use the newly developed VNS synchronized fMRI technique to examine whether VNS BOLD signal changes depend on the frequency of stimulation. Six adults with recurrent depression were scanned inside a 1.5 T MR scanner. Data were acquired at rest, with the VNS device on for 7 s, and also, for comparison, while the patient listened to a tone for 7 s. In two separate back-to-back sessions, the VNS stimulation frequency was set to either 5 or 20 Hz. Data were transformed into Talairach space and then compared by condition. Compared to 5 Hz, 20 Hz VNS produced more acute activity changes from rest in regions similar to our initial VNS synchronized fMRI feasibility study in depression. Brain regions activated by hearing a tone were also greater when VNS was intermittently being applied at 20 Hz than at 5 Hz. In depressed adults, left cervical VNS causes regional brain activity changes that depend on the frequency of stimulation or total dose, or both. In addition to the acute immediate effects of VNS on regional brain activity, this study suggests further that VNS at different frequencies likely has frequency or dose dependent modulatory effects on other brain activities (e.g. hearing a tone).