Vagus nerve stimulation therapy: A research update

Sensory Stimulation Via the Visual, Auditory, Olfactory and Gustatory Systems Can Modulate Mood and Depression

Depression is one of the most common mental disorders, predicted to be the leading cause of disease burden by the next decade. There is great deal of emphasis on the central origin and potential therapeutics of depression whereby the symptomatology of depression has been interpreted and treated as brain generated dysfunctions filtering down to the periphery. This top-down approach has found strong support from clinical work and basic neuroscientific research. Nevertheless, despite great advances in our knowledge of the etiology and therapeutics of depression, success in treatment is still by no means assured.. As a consequence, a wide net has been cast by both clinicians and researchers in search of more efficient therapies for mood disorders. As a complementary view, the present integrative review advocates approaching mood and depression from the opposite perspective: a bottom-up view that starts from the periphery. Specifically, evidence is provided to show that sensory stimulation via the visual, auditory, olfactory and gustatory systems can modulate depression. The review shows how -depending on several parameters- unisensory stimulation via these modalities can ameliorate or aggravate depressive symptoms. Moreover, the review emphasizes the bidirectional relationship between sensory stimulation and depression. Just as peripheral stimulation can modulate depression, depression in turn affects-and in most cases impairs-sensory reception. Furthermore, the review suggests that combined use of multisensory stimulation may have synergistic ameliorative effects on depressive symptoms over and above what has so far been documented for unisensory stimulation.

Cortical Responses to Vagus Nerve Stimulation Are Modulated by Brain State in Nonhuman Primates

Vagus nerve stimulation (VNS) has been tested as therapy for several brain disorders and as a means to modulate cortical excitability and brain plasticity. Cortical effects of VNS, manifesting as vagal-evoked potentials (VEPs), are thought to arise from activation of ascending cholinergic and noradrenergic systems. However, it is unknown whether those effects are modulated by brain state at the time of stimulation. In 2 freely behaving macaque monkeys, we delivered short trains of 5 pulses to the left cervical vagus nerve at different frequencies (5-300 Hz) while recording local field potentials (LFPs) from sites in contralateral prefrontal, sensorimotor and parietal cortical areas. Brain states were inferred from spectral components of LFPs and the presence of overt movement: active awake, resting awake, REM sleep and NREM sleep. VNS elicited VEPs in all sampled cortical areas. VEPs comprised early (<70 ms), intermediate (70-250 ms) and late (>250 ms) components. The magnitude of the intermediate and late components was largest during NREM sleep and smallest during wakefulness, whereas that of the early component was not modulated by brain state. VEPs during NREM were larger for stimuli delivered at the depolarized phase of ongoing delta oscillations. Higher pulsing frequencies generated larger VEPs. These short VNS trains did not affect brain state transitions during wakefulness or sleep. Our findings suggest that ongoing brain state modulates the evoked effects of VNS on cortical activity. This has implications for the role of ongoing cortical activity and brain state in shaping cortical responses to peripheral stimuli, for the modulation of vagal interoceptive signaling by cortical activity, and for the dose calibration of VNS therapies.

Is vagal-nerve stimulation safe during pregnancy? A mini review

BACKGROUND

Vagus-nerve stimulation (VNS) is the most common neuromodulation technique and has been approved by the FDA for treating refractory epilepsy and refractory depression. Although VNS has been used for nearly 32 years, the impact of VNS on the safety of pregnant women and neonate remains to be evaluated.

METHODS

We first analyze the relationship between the vagus nerve and the reproductive system (ovary and uterus) and then determine whether harm is inflicted to the reproductive system, thereby affecting the pregnancy. A comprehensive literature search is performed on PubMed/MEDLINE database, Web of Science, and Scopus. Ten articles are included in the study, and 44 pregnancies of 38 patients are analyzed.

RESULTS

The vagus nerve is connected with the reproductive system, but VNS may have little effect on pregnancy. We analyze 10 articles (38 patients with 44 pregnancies) about VNS complications during pregnancy. Two of the 44 pregnancies (2/44, 4.5 %) are miscarriages, and two pregnancies have fetuses with congenital malformations (2/42, 4.8 %), which could also be attributed to polytherapy with antiepileptic drugs. The rest of the pregnant women have no postpartum complications, and their fetuses are healthy.

CONCLUSIONS

VNS may be relatively safe and effective for the fetus and mother during pregnancy, and turning off VNS during pregnancy is unnecessary. However, owing to the small sample size and short follow-up time in the present study, further research is needed.

Heart Rate Variability Analysis in Episodic Migraine: A Cross-Sectional Study

Objective: It has been reported that autonomic nervous dysfunction is more prevalent in migraineurs. Heart rate variability (HRV) is a commonly used method to evaluate the cardiac autonomic nervous function modulation. However, HRV changes in migraine are still contradictory. The main objective of this study was to explore the potential HRV change patterns in episodic migraine (EM) and whether there were differences in HRV between EM ictal period and the interictal period.

Patients and Methods: We conducted a cross-sectional study including 18 patients with EM and 18 age- and sex-matched controls. The characteristics of demographics, some lifestyle factors, and psychological conditions were assessed at baseline. HRVs including time-domain analysis and frequency-domain analysis were performed in all participants. HRV analyses in migraine were recorded not only in the interictal period but also in the ictal period.

Results: All the HRV parameters showed a decreased trend in migraine than controls. Time-domain parameters standard deviation of all NN intervals in 24 h (SDNN) and triangular index were significantly lower in the migraine ictal period than controls separately (SDNN, 56.94 ± 22.09 ± 7.76 vs. 135.78 ± 35.16, p < 0.001; triangular index, 12.61 ± 3.20 vs. 22.11 ± 6.90, p < 0.001). Frequency-domain parameter low-frequency power was also lower in the migraine ictal period than controls (351.28 ± 206.71 vs. 559.61 ± 281.24, p = 0.02). SDNN was much lower in the migraine ictal period than migraine interictal period (56.94 ± 22.09 vs. 115.94 ± 46.88, p < 0.001). HRV changes during migraine interictal period did not differ from the control group. The correlation analysis revealed a negative correlation between visual analog scale and HRV parameters in the migraine ictal period (p = 0.04).

Conclusions: The present cross-sectional study indicates that HRV was significantly decreased in EM population especially during the migraine ictal period, which means unbalance of autonomic system in EM. Perhaps larger prospective cohort studies are wanted to validate these findings.

Neural signal recording and processing in somatic neuroprosthetic applications. A review

Neurointerfaces have acquired major relevance as both rehabilitative and therapeutic tools for patients with spinal cord injury, limb amputations and other neural disorders. Bidirectional neural interfaces are a key component for the functional control of neuroprosthetic devices. The two main neuroprosthetic applications of interfaces with the peripheral nervous system (PNS) are: the refined control of artificial prostheses with sensory neural feedback, and functional electrical stimulation (FES) systems attempting to generate motor or visceral responses in paralyzed organs. The results obtained in experimental and clinical studies with both, extraneural and intraneural electrodes are very promising in terms of the achieved functionality for the neural stimulation mode. However, the results of neural recordings with peripheral nerve interfaces are more limited. In this paper we review the different existing approaches for PNS signals recording, denoising, processing and classification, enabling their use for bidirectional interfaces. PNS recordings can provide three types of signals: i) population activity signals recorded by using extraneural electrodes placed on the outer surface of the nerve, which carry information about cumulative nerve activity; ii) spike activity signals recorded with intraneural electrodes placed inside the nerve, which carry information about the electrical activity of a set of individual nerve fibers; and iii) hybrid signals, which contain both spiking and cumulative signals. Finally, we also point out some of the main limitations, which are hampering clinical translation of neural decoding, and indicate possible solutions for improvement.

Corpus callosum low-frequency stimulation suppresses seizures in an acute rat model of focal cortical seizures

OBJECTIVE

Low-frequency fiber-tract stimulation has been shown to be effective in treating mesial temporal lobe epilepsies through activation of the hippocampal commissure in rodents and human patients. The corpus callosum is a major pathway connecting the two hemispheres of the brain; however, few experiments have documented corpus callosum stimulation. The objective is to determine the efficacy of corpus callosum stimulation at low frequencies to suppress cortical seizures.

METHODS

4-Aminopyridine was injected in the primary motor cortex of 24 rats under anesthesia. Recording electrodes were placed in the contralateral motor cortex and hippocampus. Three pairs of stimulating electrodes were inserted into the corpus callosum along its longitudinal axis. Local field potentials were recorded 1 hour before, during, and after stimulation to determine the effect of stimulation on seizure duration. Stimulation was delivered from each pair of electrodes independently in separate experiments. Furthermore, electrical stimulation was applied to the region of the corpus callosum with the highest degree of innervation of the seizure focus to compare the efficacy of different stimulation frequencies (1-30 Hz) on seizure suppression.

RESULTS

Corpus callosum stimulation was effective at suppressing seizures at 10 Hz by 76% (P < 0.05, n = 5) and at 20 Hz by 95% (P < 0.0001, n = 14). Stimulation at frequencies of 1 and 30 Hz did not have a significant effect on reducing the total time spent seizing (P > 0.9999, n = 5). Furthermore, stimulation was only effective at suppressing seizures when the pair of electrodes was placed within the section of corpus callosum containing fibers innervating the seizure focus. Secondarily generalized seizures in the hippocampus were eliminated when seizures in the cortical focus were suppressed.

SIGNIFICANCE

Low-frequency fiber-tract stimulation of the corpus callosum suppresses both cortical and cortically induced hippocampal seizures in an acute model of focal cortical seizures. The stimulation paradigm is selective, as it is only effective when targeted to specific regions of the corpus callosum that project maximally to cortical regions generating the seizure activity. Selective placement of stimulation electrodes along the corpus callosum could be used as a patient-specific treatment for cortical epilepsies.

Mefenamic Acid Attenuates Chronic Alcohol Induced Cognitive Impairment in Zebrafish: Possible Role of Cholinergic Pathway

Based on the scientific evidence supporting the neuroinflammatory response contributes the cognitive impairment associated with chronic alcoholism and the neuroprotective actions of mefenamic acid with reversal of memory loss and brain inflammation in mice, this study was designed to evaluate the effect of mefenamic acid against chronic alcohol induced cognitive impairment in zebrafish model. Zebrafish were grouped and subjected to normal behavioral analysis in light-dark chamber for 10 days. The preference to dark compartment was noted in zebrafish. Zebrafish were grouped and exposed to escalating doses of alcohol for 28 days with and without mefenamic acid exposure (100 and 200 µg/L) and subjected to a fear conditioning passive avoidance task from day 13 of 28. The cognitive evaluation was performed for 10 days and the brain tissue was isolated to estimate acetylcholinesterase activity. In cognitive evaluation study, the normal zebrafish retained the memory of the learned task and avoided the dark. The alcohol exposed zebrafish showed impairment in retaining the memory of learned task. Mefenamic acid exposed zebrafish showed a significant protection against cognitive impairment caused by alcohol and retained the memory of learned task with a significant decrease in AChE activity in brain homogenate compared to alcohol exposed zebrafish. The results of this study suggest that the memory enhancing activity of mefenamic acid might be due to activation of cholinergic transmission that has protected neuroinflammatory and neurodegenerative conditions caused by alcohol.

Chronic cuffing of cervical vagus nerve inhibits efferent fiber integrity in rat model

OBJECTIVE

Numerous studies of vagal nerve stimulation (VNS) have been published showing it to be a potential treatment for chronic inflammation and other related diseases and disorders. Studies in recent years have shown that electrical stimulation of the vagal efferent fibers can artificially modulate cytokine levels and reduce systematic inflammation. Most VNS research in the treatment of inflammation have been acute studies on rodent subjects. Our study tested VNS on freely moving animals by stimulating and recording from the cervical vagus with nerve cuff electrodes over an extended period of time.

APPROACH

We used methods of electrical stimulation, retrograde tracing (using Fluorogold) and post necropsy histological analysis of nerve tissue, flow cytometry to measure plasma cytokine levels, and MRI scanning of gastric emptying. This novel combination of methods allowed examination of physiological aspects of VNS previously unexplored.

MAIN RESULTS

Through our study of 53 rat subjects, we found that chronically cuffing the left cervical vagus nerve suppressed efferent Fluorogold transport in 43 of 44 animals (36 showed complete suppression). Measured cytokine levels and gastric emptying rates concurrently showed nominal differences between chronically cuffed rats and those tested with similar acute methods. Meanwhile, results of electrophysiological and histological tests of the cuffed nerves revealed them to be otherwise healthy, consistent with previous literature.

SIGNIFICANCE

We hypothesize that due to these unforeseen and unexplored physiological consequences of the chronically cuffed vagus nerve in a rat, that inflammatory modulation and other vagal effects by VNS may become unreliable in chronic studies. Given our findings, we submit that it would benefit the VNS community to re-examine methods used in previous literature to verify the efficacy of the rat model for chronic VNS studies.

Vagus Nerve Stimulation Alters Phase Synchrony of the Anterior Cingulate Cortex and Facilitates Decision Making in Rats

Vagus nerve stimulation (VNS) can enhance memory and cognitive functions in both rats and humans. Studies have shown that VNS influenced decision-making in epileptic patients. However, the sites of action involved in the cognitive-enhancement are poorly understood. By employing a conscious rat model equipped with vagus nerve cuff electrode, we assess the role of chronic VNS on decision-making in rat gambling task (RGT). Simultaneous multichannel-recordings offer an ideal setup to test the hypothesis that VNS may induce alterations of in both spike-field-coherence and synchronization of theta oscillations across brain areas in the anterior cingulate cortex (ACC) and basolateral amygdala (BLA). Daily VNS, administered immediately following training sessions of RGT, caused an increase in 'good decision-maker' rats. Neural spikes in the ACC became synchronized with the ongoing theta oscillations of local field potential (LFP) in BLA following VNS. Moreover, cross-correlation analysis revealed synchronization between the ACC and BLA. Our results provide specific evidence that VNS facilitates decision-making and unveils several important roles for VNS in regulating LFP and spike phases, as well as enhancing spike-phase coherence between key brain areas involved in cognitive performance. These data may serve to provide fundamental notions regarding neurophysiological biomarkers for therapeutic VNS in cognitive impairment.

Vagus Nerve Stimulator Placement in Dogs: Surgical Implantation Technique, Complications, Long-Term Follow-Up, and Practical Considerations

OBJECTIVE

To describe a modified implantation procedure of a vagus nerve stimulation (VNS) device in dogs and to report short- and long-term complications.

STUDY DESIGN

Descriptive, experimental study.

ANIMALS

Healthy, adult Beagle dogs (n = 10).

METHODS

A VNS Therapy(®) System was implanted in the left cervical region of anesthetized dogs. During and within 48 hours after surgery, electrocardiography (ECG) and impedance testing of the system were performed. Dogs were monitored daily and the impedance of the system was determined regularly until VNS devices were surgically removed 3 years after implantation.

RESULTS

The implantation procedure was successful in all dogs without intraoperative complications. ECG monitoring and impedance tests were within normal limits during and within 48 hours after surgery. Postoperative seroma formation was common (70%). One dog developed an irreversible Horner's syndrome leading to removal of the device 5 months after implantation. Another dog developed trauma-induced damage of the lead requiring surgical revision. The device could be safely removed in all dogs; however, electrodes were left in place to avoid nerve damage. At removal, the anchor tether was dislodged in 40% of dogs and the lead was twisted in 50% of dogs.

CONCLUSION

Implantation of a VNS Therapy(®) System is safe and feasible in dogs; however, seroma formation, twisting of the lead, and dislodgement of the anchor tether were common. Practical improvements in the technique include stable device placement, use of a compression bandage, and exercise restriction. Regular evaluation of lead impedance is important, as altered values can indicate serious complications.

Anti-inflammatory properties of the vagus nerve: potential therapeutic implications of vagus nerve stimulation

Brain and viscera interplay within the autonomic nervous system where the vagus nerve (VN), containing approximately 80% afferent and 20% efferent fibres, plays multiple key roles in the homeostatic regulations of visceral functions. Recent data have suggested the anti-inflammatory role of the VN. This vagal function is mediated through several pathways, some of them still debated. The first one is the anti-inflammatory hypothalamic-pituitary-adrenal axis which is stimulated by vagal afferent fibres and leads to the release of cortisol by the adrenal glands. The second one, called the cholinergic anti-inflammatory pathway, is mediated through vagal efferent fibres that synapse onto enteric neurons which release acetylcholine (ACh) at the synaptic junction with macrophages. ACh binds to α-7-nicotinic ACh receptors of those macrophages to inhibit the release of tumour necrosis (TNF)α, a pro-inflammatory cytokine. The last pathway is the splenic sympathetic anti-inflammatory pathway, where the VN stimulates the splenic sympathetic nerve. Norepinephrine (noradrenaline) released at the distal end of the splenic nerve links to the β2 adrenergic receptor of splenic lymphocytes that release ACh. Finally, ACh inhibits the release of TNFα by spleen macrophages through α-7-nicotinic ACh receptors. Understanding of these pathways is interesting from a therapeutic point of view, since they could be targeted in various ways to stimulate anti-inflammatory regulation in TNFα-related diseases such as inflammatory bowel disease and rheumatoid arthritis. Among others, VN stimulation, either as an invasive or non-invasive procedure, is becoming increasingly frequent and several clinical trials are ongoing to evaluate the potential effectiveness of this therapy to alleviate chronic inflammation.

Effects of vagus nerve stimulation on cognitive functioning in rats with cerebral ischemia reperfusion

Background

Vagus nerve stimulation (VNS) has become the most common non-pharmacological treatment for intractable drug-resistant epilepsy. However, the contribution of VNS to neurological rehabilitation following stroke has not been thoroughly examined. Therefore, we investigated the specific role of acute VNS in the recovery of cognitive functioning and the possible mechanisms involved using a cerebral ischemia/reperfusion (I/R) injury model in rats.

Methods

The I/R-related injury was modeled using occlusion and reperfusion of the middle cerebral artery (MCAO/R) in Sprague–Dawley rats. VNS was concurrently applied to the vagus nerve using a stimulation intensity of 1 mA at a fixed frequency of 20 Hz with a 0.4-ms bipolar pulse width. The stimulation duration and inter-train interval were both 3 s. Next, Morris water maze and shuttle-box behavioral experiments were conducted to assess the effects of VNS on the recovery of learning, memory, and inhibitory avoidance following I/R injury. Intracerebroventricular injection of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4), a selective neurotoxin for noradrenergic neurons, was used to evaluate the role of norepinephrine (NE) as a mediator of therapeutic effects of VNS on cognitive recovery.

Results

Compared with the MCAO/R group, the VNS+MCAO/R group had improved spatial memory as indicated by swimming path lengths and escape latencies in the Morris water maze, and fear memory, as indicated by the avoidance conditioned response rate, mean shock duration, and avoidance time in shuttle-box behavior experiments. Compared with the VNS+MCAO/R group, the DSP-4+VNS+MCAO/R group, which had reduced NE levels in cortical and hippocampal brain regions, showed a reversal of the VNS-induced benefits on spatial and fear memory performance.

Conclusions

VNS improves spatial and fear memory in a rat model of MCAO/R injury. However, a reduction in NE from the administration of DSP-4 blocks these protective effects, suggesting that NE may contribute to the influence exhibited by VNS on memory performance in rats with cerebral I/R-related injury.

Electrical stimulation of the vagus nerve protects against cerebral ischemic injury through an anti-infammatory mechanism

Vagus nerve stimulation exerts protective effects against ischemic brain injury; however, the underlying mechanisms remain unclear. In this study, a rat model of focal cerebral ischemia was established using the occlusion method, and the right vagus nerve was given electrical stimulation (constant current of 0.5 mA; pulse width, 0.5 ms; frequency, 20 Hz; duration, 30 seconds; every 5 minutes for a total of 60 minutes) 30 minutes, 12 hours, and 1, 2, 3, 7 and 14 days after surgery. Electrical stimulation of the vagus nerve substantially reduced infarct volume, improved neurological function, and decreased the expression levels of tumor necrosis factor-α and interleukin-6 in rats with focal cerebral ischemia. The experimental findings indicate that the neuroprotective effect of vagus nerve stimulation following cerebral ischemia may be associated with the inhibition of tumor necrosis factor-α and interleukin-6 expression.

Vagally mediated heart rate variability in headache patients—a systematic review and meta-analysis

Objective

Vagal nerve activity—indexed by heart rate variability (HRV)—has been linked to altered pain processing and inflammation, both of which may underpin headache disorders and lead to cardiovascular disease (CVD). Here we examined the evidence for differences in parasympathetic (vagal) activity indexed by time- and frequency-domain measures of HRV in patients with headache disorders compared to healthy controls (HCs).

Methods

A systematic review and meta-analysis was conducted on studies investigating group differences in vagally mediated HRV (vmHRV) including time- (root-mean-square of successive R-R-interval differences (RMSSD)) and frequency- (high-frequency HRV) domain measures. Studies eligible for inclusion were identified by a systematic search of the literature, based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.

Results

Seven studies reporting a total of 10 comparisons of patients with headache disorders (HF-HRV n = 67, RMSSD n = 122) and HCs (HF-HRV n = 64, RMSSD n = 125) were eligible for inclusion. Random-effects meta-analysis revealed a significant main effect on RMSSD ( Z = 2.03, p = 0.04; Hedges’ g = −0.63; 95% CI (−1.24, –0.02); k = 6) and similar pooled effect size estimates for HF-HRV when breathing was controlled ( g = −0.30; 95% CI (−0.69; 0.10)) but not when breathing was not controlled ( g = 0.02; 95% CI (−0.69; 0.74)). Controlling for breathing had no effect on RMSSD.

Conclusion

vmHRV is reduced in patients with headache disorders, findings associated with a medium effect size. Suggestions for future research in this area are provided, emphasizing a need to investigate the impact of headache disorders and commonly comorbid conditions—including mental disorders—as well as the investigation of the risk for CVD in migraine in particular. We further emphasize the need for large-scale studies to investigate HRV as a mechanism mediating the association of migraine and CVD.

Sensorimotor modulation of mood and depression: in search of an optimal mode of stimulation

Depression involves a dysfunction in an affective fronto-limbic circuitry including the prefrontal cortices, several limbic structures including the cingulate cortex, the amygdala, and the hippocampus as well as the basal ganglia. A major emphasis of research on the etiology and treatment of mood disorders has been to assess the impact of centrally generated (top-down) processes impacting the affective fronto-limbic circuitry. The present review shows that peripheral (bottom-up) unipolar stimulation via the visual and the auditory modalities as well as by physical exercise modulates mood and depressive symptoms in humans and animals and activates the same central affective neurocircuitry involved in depression. It is proposed that the amygdala serves as a gateway by articulating the mood regulatory sensorimotor stimulation with the central affective circuitry by emotionally labeling and mediating the storage of such emotional events in long-term memory. Since both amelioration and aggravation of mood is shown to be possible by unipolar stimulation, the review suggests that a psychophysical assessment of mood modulation by multimodal stimulation may uncover mood ameliorative synergisms and serve as adjunctive treatment for depression. Thus, the integrative review not only emphasizes the relevance of investigating the optimal levels of mood regulatory sensorimotor stimulation, but also provides a conceptual springboard for related future research.

Gastric electrical stimulation for the treatment of obesity: from entrainment to bezoars-a functional review

GROWING WORLDWIDE OBESITY EPIDEMIC HAS PROMPTED THE DEVELOPMENT OF TWO MAIN TREATMENT STREAMS: (a) conservative approaches and (b) invasive techniques. However, only invasive surgical methods have delivered significant and sustainable benefits. Therefore, contemporary research exploration has focused on the development of minimally invasive gastric manipulation methods featuring a safe but reliable and long-term sustainable weight loss effect similar to the one delivered by bariatric surgeries. This antiobesity approach is based on placing external devices in the stomach ranging from electrodes for gastric electrical stimulation to temporary intraluminal bezoars for gastric volume displacement for a predetermined amount of time. The present paper examines the evolution of these techniques from invasively implantable units to completely noninvasive patient-controllable implements, from a functional, rather than from the traditional, parametric point of view. Comparative discussion over the available pilot and clinical studies related to gastric electrical stimulation outlines the promises and the fallacies of this concept as a reliable alternative anti-obesity strategy.

Where in the brain is depression?

Major depressive disorder is a serious medical illness which is responsible for considerable morbidity and disability. Despite decades of research, the neural basis for depression is still incompletely understood. In this review, evidence from neuroimaging, neuropsychiatric and brain stimulations studies are explored to answer the question regarding the localization of depression in the brain. Neuroimaging studies indicate that although many regions of the brain have been repeatedly implicated in the pathophysiology of depression, not many consistent findings have been found until present. In recent times, the focus of neuroimaging has shifted from regional brain abnormalities to circuit level connectivity abnormalities. However, connectivity models are inherently more complicated, and the validity of these models remains to be tested. Neuropsychiatric studies of illnesses such as Parkinson's disease and stroke provide promising clues regarding areas involved in depression, but again consistent findings are rare. Similarly, stimulation of a variety of brain regions and circuits has been reported as being effective in depression. Therefore, the current knowledge indicates that the pathophysiology of depression may be distributed across many brain regions and circuits. In future studies, this distributed nature of depression needs to be further investigated, primary and secondary areas affected need to be identified, and new paradigms to explain complex mental functions need to be explored.

Far field potentials from brain stem after transcutaneous vagus nerve stimulation: optimization of stimulation and recording parameters

The method of vagus somatosensory evoked potentials (VSEP) was introduced to easily measure the activity of vagus brain stem nuclei. In Alzheimer's disease, this measure was characterized by longer latencies as compared to controls while amplitudes did not show statistical significant differences at frontal and central recording sites. Therefore, the influence of stimulation and recording parameters on amplitudes of VSEP were systematically examined. In 20 healthy participants, VSEP measurement was done by electrical stimulation of the cutaneous representation of the vagus nerve in the external auditory channel and recording of VSEP over the scalp. The optimum stimulation intensity is 8 mA without perception of pain. There is no effect of stimulation side or gender. Maximum VSEP amplitudes are detected at bipolar recordings comprising the electrode T4 without statistically significant differences of latencies, wave shape and polarity. Thus, recordings of future examinations should be performed at 8 mA including this temporal electrode position. The reason for focussing on brain stem evoked potentials is that recent work has accumulated evidence for this area being involved in early phases of neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Improved methodological knowledge may facilitate the assessment of this non-invasive and cost-effective method in the early diagnosis of neurodegenerative disorders.

From prefrontal leukotomy to deep brain stimulation: the historical transformation of psychosurgery and the emergence of neuroethics

The history of psychosurgery is described and analyzed. This historical perspective largely begins with analysis of the work of Egas Moniz in the development of the leukotomy, and follows the rise and fall of its popularity in the 1900s. The reemergence of psychosurgical procedures and the development of new therapeutic technologies such as vagus nerve stimulation and deep brain stimulation are discussed. In addition, an introduction to the field of neuroethics is provided, given its importance in any discussion about surgical therapy for psychiatric patients.

A pilot study of vagus nerve stimulation (VNS) for treatment-resistant anxiety disorders

BACKGROUND

Vagus nerve stimulation (VNS) is an effective anticonvulsant device and has shown antidepressant effects in chronic treatment resistant depression. Because the vagus nerve sends information to brain regions important in anxiety regulation (locus coeruleus, orbitofrontal cortex, insula, hippocampus and amygdala), this pathway might be involved in perceiving or manifesting various somatic and cognitive symptoms that characterize anxiety disorders. On the basis of this reasoning and reports of anxiolytic effects of VNS in patients treated for epilepsy and depression, we organized an open-label pilot acute trial of adjunctive VNS on top of stable medications, followed by long-term follow-up, to assess the safety and potential efficacy of VNS for patients with treatment resistant anxiety disorders.

METHODS

Eleven adult outpatients with treatment resistant obsessive-compulsive disorder (OCD), panic disorder (PD), or posttraumatic stress disorder (PTSD) were recruited. Patients had failed several medication trials as well as cognitive behavioral therapy (CBT). All patients were rated with the Hamilton Anxiety Scale (HAM-A) and the clinical global impressions improvement scale (CGI-I). Patients with OCD were also rated with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). Patients were maintained on their current psychotropic medications at fixed doses during the acute 12-week phase. Changes in medications and VNS stimulus parameters were allowed during the long-term follow-up. Response was defined as a 50% or greater improvement on the HAM-A for all patients and a 25% or greater improvement on the Y-BOCS for patients with OCD.

RESULTS

Eleven patients were recruited. Seven patients had a primary diagnosis of OCD, two had PTSD, and one had PD. One OCD patient changed their mind and was never implanted. One patient with OCD withdrew consent before the end of the acute phase, so long-term results were available for nine patients. Three patients were acute responders, based on the HAM-A, and there was some improvement in anxiety ratings over time (with statistically significant improvements at 14 of 18 quarters during long-term follow-up). Of the seven patients with OCD who received stimulation, three were acute responders, based on the Y-BOCS, and there was some improvement in Y-BOCS scores over time (with statistically significant improvements at 7 of 18 quarters during long-term follow-up). VNS was relatively well tolerated. Four years after implantation, four patients (diagnoses two OCD, one PD, one PTSD) were still receiving VNS with continued and sustained improvement in anxiety scores compared with their baseline scores.

CONCLUSIONS

These patients with treatment-resistant anxiety disorders generally tolerated VNS treatment, and there was evidence of acute and long-term improvement in some patients. These open data suggest that further double-blind studies assessing the VNS role in treating anxiety disorders, particularly OCD, may be warranted.

Pain in chronic pancreatitis: a salutogenic mechanism or a maladaptive brain response?

Pain in chronic pancreatitis is frequently refractory to medical and even surgical treatment. This refractoriness leads us to believe that a pancreas-independent, brain-mediated mechanism must be responsible. If so, several scenarios are worth considering. First, chronic pain could be the consequence of undesirable neuroplastic changes, by which pathology becomes established and causes disability. Alternatively, pain may be linked to the salutogenic (from salutogenesis, the Latin word for health and well-being) central nervous system response (we defined 'salutogenic response' as the specific modulation of the immune system induced by brain activity changes) to promote healing of the injured viscera. If so, chronic pain could index the ongoing nervous system attempt to promote healing. In this review, we discuss (1) the mechanisms of pain in chronic pancreatitis; (2) potential brain-related salutogenic mechanisms, and (3) the potential relationship of these two factors to the disease status. Furthermore, we consider these aspects in light of a new approach to treat visceral pain: transcranial magnetic stimulation, a noninvasive method of brain stimulation.

Vagus Nerve Stimulation for Severe Depression

Treatment-resistant depression is a serious problem with significant costs in terms of health care dollars and patients' well-being. Vagus nerve stimulation (VNS) is one novel, device-based therapy that may be effective in this population. In this article, we review the evidence to date on the use of VNS in major depression and describe the process of VNS treatment initiation, device implantation, and dosage adjustment and monitoring. It is important for psychiatric nurses to understand the evidence base for and how VNS is used in treatment so they may enhance care of patients with treatment-resistant depression.

Intracranial abnormalities detected by three-dimensional magnetic resonance imaging in Prader-Willi syndrome

The neuropathologic abnormalities associated with Prader-Willi syndrome (PWS) are largely unknown. PWS is due to the loss of several paternally expressed genes in chromosome 15q11-q13 region. Several of the imprinted genes in the 15q11-q13 region are normally expressed in the brain and thought to be necessary for neuronal growth and development. Thus, we hypothesized that we would find abnormalities in gray and white matter growth in individuals with PWS. We evaluated three-dimensional (3-D) MRI scans of 20 individuals with PWS, aged three months to 39 years, and compared them to 3-D MRI scans of 21 normal weight sibling controls and 16 individuals with early-onset morbid obesity (EMO) of unknown etiology. The interpreters of the scans were blinded to the diagnosis of the subjects. Intracranial abnormalities in individuals with PWS included ventriculomegaly (100% of individuals), decreased volume of brain tissue in the parietal-occipital lobe (50%), sylvian fissure polymicrogyria (60%), and incomplete insular closure (65%). None of the EMO or normal weight control subjects had any of these findings. We found multiple morphologic brain abnormalities in subjects with PWS suggesting that the loss of paternally expressed genes in chromosome 15q11-q13 region may result in abnormalities of neuronal development. The specific mechanisms underlying these neuropathological abnormalities and their correlation with the clinical phenotype remain to be elucidated.

Vagus nerve stimulation therapy in depression and epilepsy: therapeutic parameter settings

Vagus nerve stimulation (VNS) therapy is an effective adjunctive treatment for chronic or recurrent treatment-resistant depression in adults, and for pharmacoresistant epilepsy in adults and adolescents. VNS therapy is administered through an implanted pulse generator that delivers programmed electrical pulses through an implanted lead to the left vagus nerve. Programmable pulse parameters include output current, frequency, pulse width, and ON/OFF times. Within a range of typical values, individual patients respond best to different combinations of parameter settings. The physician must identify the optimum settings for each patient while balancing the goals of maximizing efficacy, minimizing side effects, and preserving battery life. Output current is gradually increased from 0.25 mA to the maximum tolerable level (maximum, 3.5 mA); typical therapeutic settings range from 1.0 to 1.5 mA. Greater output current is associated with increased side effects, including voice alteration, cough, a feeling of throat tightening, and dyspnea. Frequency is typically programmed at 20 Hz in depression and 30 Hz in epilepsy. Pulse width is typically 250 or 500 micros. The recommended initial ON time is 30 s, followed by 5 min OFF; OFF time > ON time is recommended. As with pharmacotherapy, VNS therapy must be adjusted in a gradual, systematic fashion to individualize therapy for each patient.

Vagal Nerve Stimulation: Overview and Implications for Anesthesiologists

Vagal nerve stimulation is an important adjunctive therapy for medically refractory epilepsy and major depression. Additionally, it may prove effective in treating obesity, Alzheimer's disease, and some neuropsychiatic disorders. As the number of approved indications increases, more patients are becoming eligible for surgical placement of a commercial vagal nerve stimulator (VNS). Initial VNS placement typically requires general anesthesia, and patients with previously implanted devices may present for other surgical procedures requiring anesthetic management. In this review, we will focus on the indications for vagal nerve stimulation (both approved and experimental), proposed therapeutic mechanisms for vagal nerve stimulation, and potential perioperative complications during initial VNS placement. Anesthetic considerations during initial device placement, as well as anesthetic management issues for patients with a preexisting VNS, are reviewed.

Acute and long-term VNS effects on pain perception in a case of treatment-resistant depression

Vagus Nerve Stimulation (VNS) is approved by the FDA for treatment of both epilepsy and depression. Recent work has shown that VNS acutely affects pain perception in humans, actually increasing pain sensitivity momentarily while the device is firing. It is unclear how this acutely increased sensitivity might change over time with treatment and how it might relate to longer-term therapeutic effects of VNS on pain. We describe a patient with treatment-resistant depression and a history of severe lumbar degenerative disease with resultant chronic low back pain. His depression and pain symptoms both seemed to respond to VNS. He eventually stopped all medications and remained depression and pain free for 35 months with no change in his device settings. Sixty-six months after VNS implantation and 64 months after his initial clinical antidepressant response, under single-blind conditions, we performed quantitative sensory testing with laboratory thermal pain procedures during acute VNS-on and -off conditions. Interestingly, despite a significant and profound anti-nociceptive clinical response for the previous 35 months, he had significant increases in painfulness ratings while the VNS device was actively firing compared with device-off conditions. This case suggests that VNS-induced acute increases in pain sensitivity can coexist with a clinical anti-nociceptive response. If the acutely increased sensitivity sets the stage for the slower chronic anti-pain effects, the increased acute sensitivity does not disappear. Acute and chronic effects of VNS on pain perception merit further research.

VNS and depression: current status and future directions

Vagus nerve stimulation (VNS) is an established anticonvulsant therapy in treatment-resistant patients with epilepsy. The known anatomical projections of the vagus nerve to many brain regions that have been implicated in mood disorders suggest that VNS may also have useful antidepressant effects. There has been growing interest in the potential application of VNS in the nonpharmacological management of treatment-resistant depression. Results from an open-label study, in which 59 subjects with treatment-resistant depression were treated for 10 weeks with VNS therapy, reported a 31% response rate. In a recent controlled double-blind trial of VNS and depression, short-term treatment for 10 weeks failed to demonstrate statistical improvement over sham treatment. Results from the long-term phase of this trial may be more significant, however published data are awaited.

Changes in hypothalamic-pituitary-adrenal axis measures after vagus nerve stimulation therapy in chronic depression

BACKGROUND

Little is known about the hypothalamic-pituitary-adrenal (HPA) axis stress system in chronic depression. This study examined the corticotropin-releasing hormone (CRH) challenge test in a group of patients with chronic depression, before and after 3 months of treatment with vagus nerve stimulation (VNS) therapy, and a matched group of healthy control subjects.

METHODS

Key inclusion criteria were DSM-IV-defined major depressive disorder, a history of a current episode lasting for at least 2 years, and unresponsiveness to at least two classes of antidepressant medications. Eleven test subjects and 11 matched control subjects underwent a CRH challenge.

RESULTS

There were significant reductions in depression scores over the study period. The CRH/ACTH (adrenocorticotropic hormone) responses in the depressed group before VNS implantation were significantly higher than in the healthy group and were reduced to normal values after VNS treatment. Some measures of cortisol response were elevated before treatment and were reduced to normal over the study period. The only clinical measure correlated with HPA axis alterations was reduction in atypical depressive symptom scores.

CONCLUSIONS

These preliminary results suggest that chronic depression, in contrast to acute melancholic depression, might be characterized by increased ACTH response to CRH challenge. Short-term treatment with VNS therapy was associated with normalization of this response.

Lasting accelerative effects of 1 Hz and 20 Hz electrical stimulation on cortical spreading depression: relevance for clinical applications of brain stimulation

Clinical applications of brain stimulation have been increasing during the last decade; however, the mechanisms of action remain unknown. One proposed mechanism of action is that repetitive stimulation modulates cortical excitability. Herein, we explore the question of whether repetitive electric stimulation increases cortical excitability as indexed by the cortical spreading depression. Twenty-four Wistar rats were divided into three groups according to the treatment: sham, 1-Hz and 20-Hz stimulation. Stimulation was applied to the left frontal cortex through a pair of epidurally implanted silver-wire electrodes. The cortical spreading depression-features were analysed at three time points (one day before, one day after and 2 weeks after treatment) in both the stimulated and unstimulated hemisphere. A 3 x 2 x 3 factorial anova with repeated measures showed significant differences in the main effect of time (P < 0.0001), hemisphere (P = 0.0002) and stimulation group (P = 0.008). The interaction between time vs. hemisphere vs. stimulation group was also significant (P < 0.0001). Posthoc analysis demonstrated that 1-Hz and 20-Hz repetitive electrical stimulation significantly increased the velocity of cortical spreading depression in the stimulated hemisphere. Furthermore, 20-Hz stimulation showed a greater effect on cortical spreading depression compared to 1-Hz stimulation. The results show that 1-Hz and 20-Hz repetitive electrical stimulation results in an increase in cortical spreading depression velocity that is associated with the frequency and the hemisphere of stimulation. Furthermore, the effects are found to be long lasting. We believe that these findings have strong relevance to support the clinical application of therapies involving electrical stimulation for diseases of reduced cortical excitability.

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.

Brain Blood-flow Alterations Induced by Therapeutic Vagus Nerve Stimulation in Partial Epilepsy: II. Prolonged Effects at High and Low Levels of Stimulation

PURPOSE

To measure vagus nerve stimulation (VNS)-induced cerebral blood flow (CBF) effects after prolonged VNS and to compare these effects with immediate VNS effects on CBF.

METHODS

Ten consenting partial epilepsy patients had positron emission tomography (PET) with intravenous [15O]H2O. Each had three control scans without VNS and three scans during 30 s of VNS, within 20 h after VNS began (immediate-effect study), and repeated after 3 months of VNS (prolonged study). After intrasubject subtraction of control from stimulation scans, images were anatomically transformed for intersubject averaging and superimposed on magnetic resonance imaging (MRI) for anatomic localization. Changes on t-statistical maps were considered significant at p < 0.05 (corrected for multiple comparisons).

RESULTS

During prolonged studies, CBF changes were not observed in any regions that did not have CBF changes during immediate-effect studies. During both types of studies, VNS-induced CBF increases were similarly located in the bilateral thalami, hypothalami, inferior cerebellar hemispheres, and right postcentral gyrus. During immediate-effect studies, VNS decreased bilateral hippocampal, amygdalar, and cingulate CBF and increased bilateral insular CBF; no significant CBF changes were observed in these regions during prolonged studies. Mean seizure frequency decreased by 25% over a 3-month period between immediate and prolonged PET studies, compared with 3 months before VNS began.

CONCLUSIONS

Seizure control improved during a period over which some immediate VNS-induced CBF changes declined (mainly over cortical regions), whereas other VNS-induced CBF changes persisted (mainly over subcortical regions). Altered synaptic activities at sites of persisting VNS-induced CBF changes may reflect antiseizure actions.

Current status of the utilization of antiepileptic treatments in mood, anxiety and aggression: drugs and devices

Interventions that have been utilized to control seizures in people with epilepsy have been employed by the psychiatric community to treat a variety of disorders. The purpose of this review will be to give an overview of the most prominent uses of antiepileptic drugs (AEDs) and devices like the Vagus Nerve Stimulator (VNS) and Transcranial Magnetic Stimulation (TMS) in the treatment of psychiatric disease states. By far, the most prevalent use of these interventions is in the treatment of mood disorders. AEDs have become a mainstay in the effective treatment of Bipolar Affective Disorder (BAD). The U.S. Food and Drug Administration has approved the use of valproic acid for acute mania, and lamotrigine for BAD maintenance therapy. AEDs are also effectively employed in the treatment of anxiety and aggressive disorders. Finally, VNS and TMS are emerging as possibly useful tools in the treatment of more refractory depressive illness.

Epilepsy and depression: imaging potential common factors

Patients with seizure disorders have an increased incidence of depression. This may be due in part to psychosocial factors; or side effects of antiepileptic drugs. However, there may be underlying physiologic mechanisms for the relationship. Neuroimaging studies, including structural magnetic resonance imaging, positron emission tomography measurements of cerebral glucose metabolism, and, more recently, imaging of serotonin 1A receptors, may provide additional data to explain overlapping clinical manifestations of epilepsy and depression.

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.

Complex partial seizures and depression

A long-recognized association exists between epilepsy and affective disturbance, especially depression. People with complex partial seizures that result from temporal lobe seizure foci are highly vulnerable to psychiatric disorders. Accurate diagnosis of such disorders is an important key to treatment. Interictal depression or dysphoria is the most clinically significant problem of this type. Pharmacotherapeutic treatments that have positive effects in other types of depressive illness are also effective for depression associated with epilepsy. Electroconvulsive therapy is helpful to some patients with depression that is refractory to drug treatment or psychotherapy. Surgical resection of seizure foci may lead to psychiatric improvement for some individuals, but can also have psychiatric complications.

The recognition and management of mood disorders as a comorbidity of epilepsy

Mood disorders, especially as a comorbid finding in people with medical disorders in general, and in those with epilepsy in particular, have become increasingly recognized as a serious health concern. Unfortunately, affective disorders are underrecognized, and appropriate treatment is infrequent. The consequences of poor detection of mood disorders in people with epilepsy are discussed, along with a review of risk factors and the appearance of the disorder in this population. Prevalence rates of both depressive and bipolar spectrum disorders in people with epilepsy appear to be higher than in the general population. Recent data from community samples show elevated rates of both disorders in people with epilepsy, significantly above those in people with and without other chronic diseases. Assessment issues, including the positive and negative side effects of antiepileptic drugs, are reviewed. Treatment options are discussed, along with caveats concerning the use of antidepressants in people with epilepsy, with a focus on safety, utility, and drug interactions. Electroconvulsive therapy can also be used safely in people with epilepsy, and vagus nerve stimulation may have some utility in the treatment of depressive disorders as well. However, despite improved detection methods and effective treatments, implementation of this knowledge in neurology outpatient clinics is still problematic.

Beyond the treatment of epilepsy: new applications of vagus nerve stimulation in psychiatry

Vagus nerve stimulation (VNS) in humans generally refers to stimulation of the left vagus nerve at the cervical level VNS is an established treatment largely devoid of severe side effect for medically refractory partial onset seizures and has been used in more than 16,000 patients. Over the past 5 years, applications in other neuropsychiatric disorders have been investigated with a special emphasis on depression. Recent data from an open-label, multi-center pilot study involving 60 patients suggest a potential clinical usefulness in the acute and maintenance treatment of drug-resistant depressive disorder. The perspective of VNS as along-term treatment with the advantage of assured compliance makes it an interesting technique to potentially treat drug-resistant depression. However, definite therapeutic effects of clinical significance remain to be confirmed in large placebo-controlled trial. Results of clinical pilot studies involving patients suffering from obesity and Alzheimer's disease indicate that VNS might induce weight loss and improve cognition. Besides its clinical usefulness, VNS can be used as a research tool, allowing neurophysiologic investigations of the parasympathetic system and its interactions with other parts of the central nervous system.

Neuroprotection trek--the next generation: neuromodulation I. Techniques--deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation

Neuromodulation denotes controlled electrical stimulation of the central or peripheral nervous system. The three forms of neuromodulation described in this paper-deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation-were chosen primarily for their demonstrated or potential clinical usefulness. Deep brain stimulation is a completely implanted technique for improving movement disorders, such as Parkinson's disease, by very focal electrical stimulation of the brain-a technique that employs well-established hardware (electrode and pulse generator/battery). Vagus nerve stimulation is similar to deep brain stimulation in being well-established (for the treatment of refractory epilepsy), completely implanted, and having hardware that can be considered standard at the present time. Vagus nerve stimulation differs from deep brain stimulation, however, in that afferent stimulation of the vagus nerve results in diffuse effects on many regions throughout the brain. Although use of deep brain stimulation for applications beyond movement disorders will no doubt involve placing the stimulating electrode(s) in regions other than the thalamus, subthalamus, or globus pallidus, the use of vagus nerve stimulation for applications beyond epilepsy-for example, depression and eating disorders-is unlikely to require altering the hardware significantly (although stimulation protocols may differ). Transcranial magnetic stimulation is an example of an external or non-implanted, intermittent (at least given the current state of the hardware) stimulation technique, the clinical value of which for neuromodulation and neuroprotection remains to be determined.