Transcutaneous vagus nerve stimulation modulates amygdala functional connectivity in patients with depression

Mental health during the COVID-19 pandemic and beyond: The importance of the vagus nerve for biopsychosocial resilience

The COVID-19 pandemic has led to widespread increases in mental health problems, including anxiety and depression. The development of these and other psychiatric disorders may be related to changes in immune, endocrine, autonomic, cognitive, and affective processes induced by a SARS-CoV-2 infection. Interestingly, many of these same changes can be triggered by psychosocial stressors such as social isolation and rejection, which have become increasingly common due to public policies aimed at reducing the spread of SARS-CoV-2. The present review aims to shed light on these issues by describing how viral infections and stress affect mental health. First, we describe the multi-level mechanisms linking viral infection and life stress exposure with risk for psychopathology. Then, we summarize how resilience can be enhanced by targeting vagus nerve function by, for example, applying transcutaneous vagus nerve stimulation and targeting lifestyle factors, such as exercise. With these biopsychosocial insights in mind, researchers and healthcare professionals will be better equipped to reduce risk for psychopathology and increase resilience during this challenging pandemic period and beyond.

Vagus nerve stimulation in brain diseases: Therapeutic applications and biological mechanisms

Brain diseases, including neurodegenerative, cerebrovascular and neuropsychiatric diseases, have posed a deleterious threat to human health and brought a great burden to society and the healthcare system. With the development of medical technology, vagus nerve stimulation (VNS) has been approved by the Food and Drug Administration (FDA) as an alternative treatment for refractory epilepsy, refractory depression, cluster headaches, and migraines. Furthermore, current evidence showed promising results towards the treatment of more brain diseases, such as Parkinson's disease (PD), autistic spectrum disorder (ASD), traumatic brain injury (TBI), and stroke. Nonetheless, the biological mechanisms underlying the beneficial effects of VNS in brain diseases remain only partially elucidated. This review aims to delve into the relevant preclinical and clinical studies and update the progress of VNS applications and its potential mechanisms underlying the biological effects in brain diseases.

Exposure to Blue Wavelength Light Is Associated With Increases in Bidirectional Amygdala-DLPFC Connectivity at Rest

Blue wavelength light has been used successfully as a treatment method for certain mood disorders, but, the underlying mechanisms behind the mood enhancing effects of light remain poorly understood. We investigated the effects of a single dose of 30 min of blue wavelength light (n = 17) vs. amber wavelength light (n = 12) exposure in a sample of healthy adults on subsequent resting-state functional and directed connectivity, and associations with changes in state affect. Individuals who received blue vs. amber wavelength light showed greater positive connectivity between the right amygdala and a region within the left dorsolateral prefrontal cortex (DLPFC). In addition, using granger causality, the findings showed that individuals who received blue wavelength light displayed greater bidirectional information flow between these two regions relative to amber light. Furthermore, the strength of amygdala-DLPFC functional connectivity was associated with greater decreases in negative mood for the blue, but not the amber light condition. Blue light exposure may positively influence mood by modulating greater information flow between the amygdala and the DLPFC, which may result in greater engagement of cognitive control strategies that are needed to perceive and regulate arousal and mood.

International Consensus Based Review and Recommendations for Minimum Reporting Standards in Research on Transcutaneous Vagus Nerve Stimulation (Version 2020)

Given its non-invasive nature, there is increasing interest in the use of transcutaneous vagus nerve stimulation (tVNS) across basic, translational and clinical research. Contemporaneously, tVNS can be achieved by stimulating either the auricular branch or the cervical bundle of the vagus nerve, referred to as transcutaneous auricular vagus nerve stimulation(VNS) and transcutaneous cervical VNS, respectively. In order to advance the field in a systematic manner, studies using these technologies need to adequately report sufficient methodological detail to enable comparison of results between studies, replication of studies, as well as enhancing study participant safety. We systematically reviewed the existing tVNS literature to evaluate current reporting practices. Based on this review, and consensus among participating authors, we propose a set of minimal reporting items to guide future tVNS studies. The suggested items address specific technical aspects of the device and stimulation parameters. We also cover general recommendations including inclusion and exclusion criteria for participants, outcome parameters and the detailed reporting of side effects. Furthermore, we review strategies used to identify the optimal stimulation parameters for a given research setting and summarize ongoing developments in animal research with potential implications for the application of tVNS in humans. Finally, we discuss the potential of tVNS in future research as well as the associated challenges across several disciplines in research and clinical practice.

Effects of acute transcutaneous vagus nerve stimulation on emotion recognition in adolescent depression

BACKGROUND

Transcutaneous vagus nerve stimulation (tVNS) is a promising therapeutic option for major depressive disorder (MDD) in adults. Alternative third-line treatments for MDD in adolescents are scarce. Here we aimed to assess the effects of acute tVNS on emotion recognition in adolescents with MDD.

METHODS

Adolescents (14-17 years) with MDD (n = 33) and non-depressed controls (n = 30) received tVNS or sham-stimulation in a cross-sectional, case-control, within-subject cross-randomized controlled trial, while performing different tasks assessing emotion recognition. Correct responses, response times, and errors of omission and commission on three different computerized emotion recognition tasks were assessed as main outcomes. Simultaneous recordings of electrocardiography and electro dermal activity, as well as sampling of saliva for the determination of α-amylase, were used to quantify the effects on autonomic nervous system function.

RESULTS

tVNS had no effect on the recognition of gradually or static expressed emotions but altered response inhibition on the emotional Go/NoGo-task. Specifically, tVNS increased the likelihood of omitting a response toward sad target-stimuli in adolescents with MDD, while decreasing errors (independent of the target emotion) in controls. Effects of acute tVNS on autonomic nervous system function were found in non-depressed controls only.

CONCLUSIONS

Acute tVNS alters the recognition of briefly presented facial expressions of negative valence in adolescents with MDD while generally increasing emotion recognition in controls. tVNS seems to specifically alter early visual processing of stimuli of negative emotional valence in MDD. These findings suggest a potential therapeutic benefit of tVNS in adolescent MDD that requires further evaluation within clinical trials.

Use of Transcutaneous Auricular Vagus Nerve Stimulation as an Adjuvant Therapy for the Depressive Symptoms of COVID-19: A Literature Review

The coronavirus disease 2019 (COVID-19) comprises more than just severe acute respiratory syndrome. It also interacts with the cardiovascular, nervous, renal, and immune systems at multiple levels, increasing morbidity in patients with underlying cardiometabolic conditions and inducing myocardial injury or dysfunction. Transcutaneous auricular vagus nerve stimulation (taVNS), which is derived from auricular acupuncture, has become a popular therapy that is increasingly accessible to the general public in modern China. Here, we begin by outlining the historical background of taVNS, and then describe important links between dysfunction in proinflammatory cytokine release and related multiorgan damage in COVID-19. Furthermore, we emphasize the important relationships between proinflammatory cytokines and depressive symptoms. Finally, we discuss how taVNS improves immune function via the cholinergic anti-inflammatory pathway and modulates brain circuits via the hypothalamic-pituitary-adrenal axis, making taVNS an important treatment for depressive symptoms on post-COVID-19 sequelae. Our review suggests that the link between anti-inflammatory processes and brain circuits could be a potential target for treating COVID-19-related multiorgan damage, as well as depressive symptoms using taVNS.

Significance of gastrointestinal tract in the therapeutic mechanisms of exercise in depression: Synchronism between brain and intestine through GBA

Researchers have made considerable progress in elucidating psychological and exercise correlates of major depressive disorder (MDD). However, as the largest immune organ, far less is known about the role of gastrointestinal (GI) tract in the therapeutic mechanisms of exercise in MDD. In addition to the sites of the digestive tract that absorb nutrients, the GI tract also serves as a protective barrier against organisms. Inflammation and other consequences caused by disrupted GI barrier integrity are considered to be one of the mechanisms of depression, and the gut-brain axis (GBA) plays a critical role in this process. In this work, we observed the depression-like behaviors, intestinal barrier, central and peripheral inflammation, and related neurotransmitters through exercise intervention in the chronic unpredictable mild stress (CUMS) model, aiming to clarify the mechanisms of exercise to improve depression through GBA. Our results revealed that, following increased expressions of pro-inflammatory factors in intestine of CUMS mice, the levels of pro-inflammatory factors were all significantly raised in serum and brain simultaneously. Further, glial cells were activated in visceral nervous system and its related brain regions at the same time, accompanied by lower expression of occludin in CUMS mice. Importantly, our findings provide the first evidence that eight weeks of running exercise effectively inhibited neuro-immune interactions along gut-brain-axis and contributed obvious improvement of intestinal epithelial barrier (IEB). Finally, multivariate analysis putatively highlighted the role of exercise-induced IEB protection on depression treatment. We hope that our findings could warrant further study of therapeutic mechanisms of exercise in depression, specifically in disentangling the roles of intestinal function and IEB protection, and for developing more targeted clinical depression interventions.

The Instant Effects of Continuous Transcutaneous Auricular Vagus Nerve Stimulation at Acupoints on the Functional Connectivity of Amygdala in Migraine without Aura: A Preliminary Study

Background

A growing body of evidence suggests that both auricular acupuncture and transcutaneous auricular vagus nerve stimulation (taVNS) can induce antinociception and relieve symptoms of migraine. However, their instant effects and central treatment mechanism remain unclear. Many studies proved that the amygdalae play a vital role not only in emotion modulation but also in pain processing. In this study, we investigated the modulation effects of continuous taVNS at acupoints on the FC of the bilateral amygdalae in MwoA.

Methods

Thirty episodic migraineurs were recruited for the single-blind, crossover functional magnetic resonance imaging (fMRI) study. Each participant attended two kinds of eight-minute stimulations, taVNS and sham-taVNS (staVNS), separated by seven days in random order. Finally, 27 of them were included in the analysis of seed-to-voxel FC with the left/right amygdala as seeds.

Results

Compared with staVNS, the FC decreased during taVNS between the left amygdala and left middle frontal gyrus (MFG), left dorsolateral superior frontal gyrus, right supplementary motor area (SMA), bilateral paracentral lobules, bilateral postcingulum gyrus, and right frontal superior medial gyrus, so did the FC of the right amygdala and left MFG. A significant positive correlation was observed between the FC of the left amygdala and right SMA and the frequency/total time of migraine attacks during the preceding four weeks.

Conclusion

Continuous taVNS at acupoints can modulate the FC between the bilateral amygdalae and pain-related brain regions in MwoA, involving the limbic system, default mode network, and pain matrix, with obvious differences between the left amygdala and the right amygdala. The taVNS may produce treatment effects by modulating the abnormal FC of the amygdala and pain networks, possibly having the same central mechanism as auricular acupuncture.

Transcutaneous Vagus Nerve Stimulation in Humans Induces Pupil Dilation and Attenuates Alpha Oscillations

Vagus nerve stimulation (VNS) is widely used to treat drug-resistant epilepsy and depression. While the precise mechanisms mediating its long-term therapeutic effects are not fully resolved, they likely involve locus coeruleus (LC) stimulation via the nucleus of the solitary tract, which receives afferent vagal inputs. In rats, VNS elevates LC firing and forebrain noradrenaline levels, whereas LC lesions suppress VNS therapeutic efficacy. Noninvasive transcutaneous VNS (tVNS) uses electrical stimulation that targets the auricular branch of the vagus nerve at the cymba conchae of the ear. However, the extent to which tVNS mimics VNS remains unclear. Here, we investigated the short-term effects of tVNS in healthy human male volunteers (n = 24), using high-density EEG and pupillometry during visual fixation at rest. We compared short (3.4 s) trials of tVNS to sham electrical stimulation at the earlobe (far from the vagus nerve branch) to control for somatosensory stimulation. Although tVNS and sham stimulation did not differ in subjective intensity ratings, tVNS led to robust pupil dilation (peaking 4-5 s after trial onset) that was significantly higher than following sham stimulation. We further quantified, using parallel factor analysis, how tVNS modulates idle occipital alpha (8-13Hz) activity identified in each participant. We found greater attenuation of alpha oscillations by tVNS than by sham stimulation. This demonstrates that tVNS reliably induces pupillary and EEG markers of arousal beyond the effects of somatosensory stimulation, thus supporting the hypothesis that tVNS elevates noradrenaline and other arousal-promoting neuromodulatory signaling, and mimics invasive VNS.SIGNIFICANCE STATEMENT Current noninvasive brain stimulation techniques are mostly confined to modulating cortical activity, as is typical with transcranial magnetic or transcranial direct/alternating current electrical stimulation. Transcutaneous vagus nerve stimulation (tVNS) has been proposed to stimulate subcortical arousal-promoting nuclei, though previous studies yielded inconsistent results. Here we show that short (3.4 s) tVNS pulses in naive healthy male volunteers induced transient pupil dilation and attenuation of occipital alpha oscillations. These markers of brain arousal are in line with the established effects of invasive VNS on locus coeruleus-noradrenaline signaling, and support that tVNS mimics VNS. Therefore, tVNS can be used as a tool for studying how endogenous subcortical neuromodulatory signaling affects human cognition, including perception, attention, memory, and decision-making; and also for developing novel clinical applications.

Application of Noninvasive Vagal Nerve Stimulation to Stress-Related Psychiatric Disorders

BACKGROUND

Vagal Nerve Stimulation (VNS) has been shown to be efficacious for the treatment of depression, but to date, VNS devices have required surgical implantation, which has limited widespread implementation.

METHODS

New noninvasive VNS (nVNS) devices have been developed which allow external stimulation of the vagus nerve, and their effects on physiology in patients with stress-related psychiatric disorders can be measured with brain imaging, blood biomarkers, and wearable sensing devices. Advantages in terms of cost and convenience may lead to more widespread implementation in psychiatry, as well as facilitate research of the physiology of the vagus nerve in humans. nVNS has effects on autonomic tone, cardiovascular function, inflammatory responses, and central brain areas involved in modulation of emotion, all of which make it particularly applicable to patients with stress-related psychiatric disorders, including posttraumatic stress disorder (PTSD) and depression, since dysregulation of these circuits and systems underlies the symptomatology of these disorders.

RESULTS

This paper reviewed the physiology of the vagus nerve and its relevance to modulating the stress response in the context of application of nVNS to stress-related psychiatric disorders.

CONCLUSIONS

nVNS has a favorable effect on stress physiology that is measurable using brain imaging, blood biomarkers of inflammation, and wearable sensing devices, and shows promise in the prevention and treatment of stress-related psychiatric disorders.

Extinction Learning as a Potential Mechanism Linking High Vagal Tone with Lower PTSD Symptoms among Abused Youth

Childhood abuse is a potent risk factor for psychopathology, including posttraumatic stress disorder (PTSD). Research has shown high resting vagal tone, a measure of parasympathetic nervous system function, protects abused youth from developing internalizing psychopathology, but potential mechanisms explaining this effect are unknown. We explored fear extinction learning as a possible mechanism underlying the protective effect of vagal tone on PTSD symptoms among abused youth. We measured resting respiratory sinus arrhythmia (RSA) and skin conductance responses (SCR) during a fear conditioning and extinction task in youth with variability in abuse exposure (N = 94; aged 6-18 years). High RSA predicted lower PTSD symptoms and enhanced extinction learning among abused youths. In a moderated-mediation model, extinction learning mediated the association of abuse with PTSD symptoms only among youth with high RSA. These findings highlight extinction learning as a possible mechanism linking high vagal tone to decreased risk for PTSD symptoms among abused youth.

Vagus nerve stimulation boosts the drive to work for rewards

Interoceptive feedback transmitted via the vagus nerve plays a vital role in motivation by tuning actions according to physiological needs. Whereas vagus nerve stimulation (VNS) reinforces actions in animals, motivational effects elicited by VNS in humans are still largely elusive. Here, we applied non-invasive transcutaneous auricular VNS (taVNS) on the left or right ear while participants exerted effort to earn rewards using a randomized cross-over design (vs. sham). In line with preclinical studies, acute taVNS enhances invigoration of effort, and stimulation on the left side primarily facilitates invigoration for food rewards. In contrast, we do not find conclusive evidence that acute taVNS affects effort maintenance or wanting ratings. Collectively, our results suggest that taVNS enhances reward-seeking by boosting invigoration, not effort maintenance and that the stimulation side affects generalization beyond food reward. Thus, taVNS may enhance the pursuit of prospective rewards which may pave avenues to treat motivational deficiencies.

The vagus nerve transmits signals between the gut and the brain thereby tuning motivated behavior to physiological needs. Here, the authors show that acute non-invasive stimulation of the vagus nerve via the ear enhances the invigoration of effort for rewards.

The Efficacy and Safety of Neuromodulation Treatments in Late-Life Depression

Purpose of review

In this review, the efficacy and safety of FDA approved neuromodulation devices (electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS) and vagus nerve stimulation (VNS)), as well as emerging neuromodulation treatments currently under investigation.

Recent findings

ECT is the "gold standard" somatic therapy for treatment resistant depression (TRD). Although the clinical benefits are outweighed by potential cognitive and cardiovascular side effects in majority of cases, it remains unfairly stigmatized. TMS has few cognitive or somatic side effects but is not as effective the treatment of psychotic depression or more treatment resistant depression in elders. VNS has limited data in older patients but has been shown to be effective in chronic, treatment resistant adults. Several investigative neuromodulation treatments including magnetic seizure therapy (MST), focal electrically administered seizure therapy (FEAST), transcutaneous VNS (tVNS), transcranial direct current stimulation (tDCS), and deep brain simulation (DBS) shown promise in geriatric TRD.

Summary

ECT, TMS and VNS are effective treatment for late-life depression, and research has continued to refine the techniques. Investigative neuromodulation techniques are promising, but evidence for the safety and efficacy of these devices in the geriatric population is needed.

Efficacy and brain mechanism of transcutaneous auricular vagus nerve stimulation for adolescents with mild to moderate depression: Study protocol for a randomized controlled trial

BACKGROUND

Depression is a common mental illness in childhood and adolescence, with an incidence of 4%-5%; it can lead to impairments in learning and social functioning. Transcutaneous auricular vagus nerve stimulation (taVNS) is a commonly used method of auricular acupuncture point stimulation, which is regarded as an effective treatment for adults with depression. The aim of this study was to investigate the efficacy and mechanism of taVNS for adolescents with mild to moderate depression.

METHODS

This randomized controlled clinical trial will include 120 patients aged 12-16 years, all of whom are diagnosed with mild to moderate depression. Patients will be randomly assigned to a taVNS group and a drug control group (sertraline hydrochloride) at a ratio of 1:1. Patients will be evaluated using the 17-item Hamilton Depression Scale, Hamilton Anxiety Rating Scale, Self-Rating Depression Scale, Self-Rating Anxiety Scale, and Pittsburgh Sleep Quality Index scores at baseline, as well as at the 2nd, 4th, 6th, 8th, and 12th weeks. To investigate the underlying neural mechanisms of taVNS treatment from the perspective of the default mode network, multimodal magnetic resonance imaging (MRI; i.e., structural MRI [sMRI], resting state MRI [rsMRI], and pseudocontinuous arterial spin-labeled [pcASL] MRI) will be used to compare cerebral images among groups. MRI data will also be collected from 40 healthy volunteers to assess whether the participants exhibit normal development of structural and functional components.

DISCUSSION

Depression is the most common mental disorder in adolescence. Drug treatment can improve depression symptoms; however, the side effects of drug treatments are often severe. This study proposes a simple physiotherapy that aims to treat adolescents with mild to moderate depression. The mechanism of taVNS in the treatment of depression will also be investigated. The results of this study will provide evidence to guide the application of taVNS in adolescents with depression.

Stimulation of the vagus nerve reduces learning in a go/no-go reinforcement learning task

When facing decisions to approach rewards or to avoid punishments, we often figuratively go with our gut, and the impact of metabolic states such as hunger on motivation are well documented. However, whether and how vagal feedback signals from the gut influence instrumental actions is unknown. Here, we investigated the effect of non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) vs. sham (randomized cross-over design) on approach and avoidance behavior using an established go/no-go reinforcement learning paradigm in 39 healthy human participants (23 female) after an overnight fast. First, mixed-effects logistic regression analysis of choice accuracy showed that taVNS acutely impaired decision-making, p = .041. Computational reinforcement learning models identified the cause of this as a reduction in the learning rate through taVNS (∆α = -0.092, p_boot = .002), particularly after punishment (∆α_Pun = -0.081, p_boot = .012 vs. ∆α_Rew =-0.031, p_boot = .22). However, taVNS had no effect on go biases, Pavlovian response biases or response time. Hence, taVNS appeared to influence learning rather than action execution. These results highlight a novel role of vagal afferent input in modulating reinforcement learning by tuning the learning rate according to homeostatic needs.

New neuromodulation techniques for treatment resistant depression

In the treatment of depression, when pharmacotherapy, psychotherapy and the oldest brain stimulation techniques are deadlocked, the emergence of new therapies is a necessary development. The field of neuromodulation is very broad and controversial. This article provides an overview of current progress in the technological advances in neuromodulation and neurostimulation treatments for treatment-resistant depression: magnetic seizure therapy; focal electrically administered seizure therapy; low field magnetic stimulation; transcranial pulsed electromagnetic fields; transcranial direct current stimulation; epidural cortical stimulation; trigeminal nerve stimulation; transcutaneous vagus nerve stimulation; transcranial focussed ultrasound; near infra-red transcranial radiation; closed loop stimulation. The role of new interventions is expanding, probably with more efficacy. Nowadays, still under experimentation, neuromodulation will probably revolutionise the field of neuroscience. At present, major efforts are still necessary before that these therapies are likely to become widespread.Key pointsThere is a critical need for new therapies for treatment resistant depression.Newer therapies are expanding. In the future, these therapies, as an evidence-based adjunctive treatments, could offer a good therapeutic choice for the patients with a TRD.The current trend in the new neuromodulation therapies is to apply a personalised treatment.These news therapies can be complementary.That treatment approaches can provide clinically significant benefits.

New Somatic Treatments for Child and Adolescent Depression

PURPOSE OF REVIEW

Depression is a common clinical problem in youth, with prevalence increasing significantly during the adolescent period. Although several evidence-based treatments are currently available for treating depression in adults, only a subset of these have been investigated in a pediatric sample. Unfortunately, even well-established, first-line interventions do not lead to sufficient treatment response for many children and adolescents suffering from depression. However, recent research has been conducted in the area of somatic treatments for youth with depression. This review focuses on current (past three years, including published results and ongoing studies) research on somatic treatments for adolescent depression in the following categories: psychopharmacology, nutraceuticals, interventions implicating motor and sensory systems, and neuromodulation.

FINDINGS

Results from recent randomized, controlled trials testing psychopharmacological options suggest that while antidepressants that have been recently approved for adult patients are safe and tolerable in children and adolescents, none have yet outperformed performed placebo in efficacy. Nutraceuticals, motor-sensory interventions, and neuromodulation techniques, present safe and promising results, but few have been tested against controls to support effectiveness over current treatment options.

SUMMARY

This review of research on pediatric depression treatment from the past 3 years highlights some disappointments (negative results following some of the well-designed clinical trials) and gaps (preliminary studies in need of follow up with robust methodology) but also some promising directions in research of the efficacyof these treatments in a pediatric sample. We offer suggestions for future research including consideration of treatment timing, sequencing, the role of symptom severity in directing treatment selection, the potential value of combined treatments, consideration of how to best account for high placebo response rates, and the incorporation of neurobiological assessments to examine mechanisms and biomarker predictors of treatment response.

The anatomical basis for transcutaneous auricular vagus nerve stimulation

The array of end organ innervations of the vagus nerve, coupled with increased basic science evidence, has led to vagus nerve stimulation (VNS) being explored as a management option in a number of clinical disorders, such as heart failure, migraine and inflammatory bowel disease. Both invasive (surgically implanted) and non-invasive (transcutaneous) techniques of VNS exist. Transcutaneous VNS (tVNS) delivery systems rely on the cutaneous distribution of vagal afferents, either at the external ear (auricular branch of the vagus nerve) or at the neck (cervical branch of the vagus nerve), thus obviating the need for surgical implantation of a VNS delivery device and facilitating further investigations across a wide range of uses. The concept of electrically stimulating the auricular branch of the vagus nerve (ABVN), which provides somatosensory innervation to several aspects of the external ear, is relatively more recent compared with cervical VNS; thus, there is a relative paucity of literature surrounding its operation and functionality. Despite the increasing body of research exploring the therapeutic uses of auricular transcutaneous VNS (tVNS), a comprehensive review of the cutaneous, intracranial and central distribution of ABVN fibres has not been conducted to date. A review of the literature exploring the neuroanatomical basis of this neuromodulatory therapy is therefore timely. Our review article explores the neuroanatomy of the ABVN with reference to (1) clinical surveys examining Arnold's reflex, (2) cadaveric studies, (3) fMRI studies, (4) electrophysiological studies, (5) acupuncture studies, (6) retrograde tracing studies and (7) studies measuring changes in autonomic (cardiovascular) parameters in response to auricular tVNS. We also provide an overview of the fibre composition of the ABVN and the effects of auricular tVNS on the central nervous system. Cadaveric studies, of which a limited number exist in the literature, would be the 'gold-standard' approach to studying the cutaneous map of the ABVN; thus, there is a need for more such studies to be conducted. Functional magnetic resonance imaging (fMRI) represents a useful surrogate modality for discerning the auricular sites most likely innervated by the ABVN and the most promising locations for auricular tVNS. However, given the heterogeneity in the results of such investigations and the various limitations of using fMRI, the current literature lacks a clear consensus on the auricular sites that are most densely innervated by the ABVN and whether the brain regions secondarily activated by electrical auricular tVNS depend on specific parameters. At present, it is reasonable to surmise that the concha and inner tragus are suitable locations for vagal modulation. Given the therapeutic potential of auricular tVNS, there remains a need for the cutaneous map of the ABVN to be further refined and the effects of various stimulation parameters and stimulation sites to be determined.

Transcutaneous auricular vagus nerve stimulation at 1 Hz modulates locus coeruleus activity and resting state functional connectivity in patients with migraine: An fMRI study

Background

Migraine is a common episodic neurological disorder. Literature has shown that transcutaneous auricular vagus nerve stimulation (taVNS) at 1 Hz can significantly relieve migraine symptoms. However, its underlying mechanism remains unclear. This study aims to investigate the neural pathways associated with taVNS treatment of migraine.

Methods

Twenty-nine patients with migraine were recruited from outpatient neurology clinics. Each patient attended two magnetic resonance imaging/functional magnetic resonance imaging (MRI/fMRI) scan sessions separated by one week. Each session included a pre-stimulation resting state fMRI scan, fMRI scans during real or sham 1 Hz taVNS (with block design), and a post-stimulation resting state fMRI scan.

Results

Twenty-six patients were included in the final analyses. Real taVNS evoked fMRI signal decreases in brain areas belonging to the default mode network (DMN) and brain stem areas including the locus coeruleus (LC), raphe nuclei, parabrachial nucleus, and solitary nucleus. Sham taVNS evoked fMRI signal decreases in brain areas belonging to the DMN. Compared to sham taVNS, real taVNS produced greater deactivation at the bilateral LC. Resting state functional connectivity (rsFC) analysis showed that after taVNS, LC rsFC with the right temporoparietal junction and left secondary somatosensory cortex (S2) significantly increased compared to sham taVNS. The increased rsFC of the left LC-left S2 was significantly negatively associated with the frequency of migraine attacks during the preceding month.

Conclusion

Our results suggest that taVNS at 1 Hz can significantly modulate activity/connectivity of brain regions associated with the vagus nerve central pathway and pain modulation system, which may shed light on the neural mechanisms underlying taVNS treatment of migraine.

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taVNS at l HZ evoked fMRI signal decrease in the locus coeruleus in migraine.

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After taVNS, LC rsFC with TPJ, hippocampus and S2 increased in migraine.

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The increased LC-S2 rsFC negatively associated with the frequency of migraine attacks.

Modulatory effects of different exercise modalities on the functional connectivity of the periaqueductal grey and ventral tegmental area in patients with knee osteoarthritis: a randomised multimodal magnetic resonance imaging study

BACKGROUND

Knee osteoarthritis is a prevalent disorder with unsatisfactory treatment options. Both physical and mindful exercises may be able to relieve its pain symptoms. We compared the modulatory effects of different exercise modalities on the periaqueductal grey (PAG) and ventral tegmental area (VTA), which play important roles in descending opioidergic pathways and reward/motivation systems in patients with knee osteoarthritis.

METHODS

We recruited and randomised 140 patients into Tai Chi, Baduanjin, stationary cycling, and health education control groups for 12 weeks. Knee injury and Osteoarthritis Outcome Score (KOOS), functional and structural MRI, and blood biomarkers were measured at the beginning and end of the experiment. We used the PAG and VTA as seeds in resting-state functional connectivity (rsFC) analysis.

RESULTS

Compared with the control group: (i) all exercises significantly increased KOOS pain sub-scores (pain reduction) and serum programmed death 1 (PD-1) concentrations; (ii) all exercises decreased right PAG rsFC with the medial orbital prefrontal cortex, and the decreased rsFC was associated with improvements in knee pain; and (iii) grey matter volume in the medial orbital prefrontal cortex was significantly increased in all exercise groups. There was also significantly decreased rsFC between the left VTA and the medial orbital prefrontal cortex in the Tai Chi and Baduanjin groups.

CONCLUSIONS

Exercise can simultaneously modulate the rsFC of the descending opioidergic pathway and reward/motivation system and blood inflammation markers. Elucidating the shared and unique mechanisms of different exercise modalities may facilitate the development of exercise-based interventions for chronic pain.

CLINICAL TRIAL REGISTRATION

ChiCTR-IOR-16009308.

Mind-body exercise improves cognitive function and modulates the function and structure of the hippocampus and anterior cingulate cortex in patients with mild cognitive impairment

Mild cognitive impairment (MCI) is a common neurological disorder. This study aims to investigate the modulation effect of Baduanjin (a popular mind-body exercise) on MCI. 69 patients were randomized to Baduanjin, brisk walking, or an education control group for 24 weeks. The Montreal Cognitive Assessment (MoCA) and Magnetic Resonance Imaging scans were applied at baseline and at the end of the experiment. Compared to the brisk walking and control groups, the Baduanjin group experienced significantly increased MoCA scores. Amplitude of low-frequency fluctuations (ALFF) analysis showed significantly decreased ALFF values in the right hippocampus (classic low-freqency band, 0.01-0.08 Hz) in the Baduanjin group compared to the brisk walking group and increased ALFF values in the bilateral anterior cingulate cortex (ACC, slow-5 band, 0.01-0.027 Hz) in the Baduanjin group compared to the control group. Further, ALFF value changes in the right hippocampus and bilateral ACC were significantly associated with corresponding MoCA score changes across all groups. We also found increased gray matter volume in the Baduanjin group in the right hippocampus compared to the brisk walking group and in the bilateral ACC compared to the control group. In addition, there was an increased resting state functional connectivity between the hippocampus and right angular gyrus in the Baduanjin group compared to the control group. Our results demonstrate the potential of Baduanjin for the treatment of MCI.

Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity

Contemplative practices, such as meditation and yoga, are increasingly popular among the general public and as topics of research. Beneficial effects associated with these practices have been found on physical health, mental health and cognitive performance. However, studies and theories that clarify the underlying mechanisms are lacking or scarce. This theoretical review aims to address and compensate this scarcity. We will show that various contemplative activities have in common that breathing is regulated or attentively guided. This respiratory discipline in turn could parsimoniously explain the physical and mental benefits of contemplative activities through changes in autonomic balance. We propose a neurophysiological model that explains how these specific respiration styles could operate, by phasically and tonically stimulating the vagal nerve: respiratory vagal nerve stimulation (rVNS). The vagal nerve, as a proponent of the parasympathetic nervous system (PNS), is the prime candidate in explaining the effects of contemplative practices on health, mental health and cognition. We will discuss implications and limitations of our model.

Limbic Intrinsic Connectivity in Depressed and High-Risk Youth

OBJECTIVE

Depression runs in families and has been associated with dysfunctional limbic connectivity. Whether aberrant limbic connectivity is a risk factor for or a consequence of depression is unclear. To examine this question, we compared resting state functional connectivity (RSFC) in youth with depressive disorders (DEP), healthy offspring of parents with depression (DEP-risk), and healthy comparison (HC) youth.

METHOD

Magnetic resonance imaging at rest was acquired from 119 youth, aged 8 to 17 years (DEP, n = 41, DEP-risk, n = 39, and HC, n = 39) and analyzed using seed-based RSFC in bilateral amygdala and nucleus accumbens (NAcc), covarying for age, IQ, and sex.

RESULTS

We found distinct risk- and disorder-specific patterns of RSFC across groups. DEP-risk and DEP youth shared reduced negative amygdala-right frontal cortex RSFC and reduced positive amygdala-lingual gyrus RSFC compared to HC youth (p < .001). DEP-risk youth had weaker negative amygdala-precuneus RSFC compared to DEP and HC youth (p < .001), suggesting a resilience marker for depression. In contrast, DEP youth had increased positive NAcc-left frontal cortex RSFC and reduced positive NAcc-insula RSFC compared to DEP-risk and HC youth (p < .001), suggestive of disorder-specific features of depression. Greater depression severity was correlated with disorder-specific amygdala and NAcc RSFC (p < .05).

CONCLUSION

RSFC in the amygdala and NAcc may represent selective disorder- and risk-specific markers in youth with, and at familial risk for, depression. Longitudinal studies are needed to determine whether these patterns predict long-term clinical outcomes.

The Future of Brain Stimulation Treatments

Trends in brain stimulation include becoming less invasive, more focal, and more durable with less toxicity. Several of the more interesting new potentially disruptive technologies that are just making their way through basic and sometimes clinical research studies include low-intensity focused ultrasound and temporally interfering electric fields. It is possible, and even likely, that noninvasive brain stimulation may become the dominant form of brain treatments over the next 20 years. The future of brain stimulation therapeutics is bright.

Frequency-dependent functional connectivity of the nucleus accumbens during continuous transcutaneous vagus nerve stimulation in major depressive disorder

Transcutaneous vagus nerve stimulation (tVNS) may be a promising treatment for major depressive disorder (MDD). In this exploratory study, fMRI scans were acquired during continuous real or sham tVNS from 41 MDD patients. Then, all patients received real or sham tVNS treatment for four weeks. We investigated the functional connectivity (FC) of the nucleus accumbens (NAc) at different frequency bands during real and sham tVNS and explored their associations with depressive symptom changes after one month of treatment. The results revealed: 1) significant positive FCs between the NAc and surrounding areas including the putamen, caudate, and distinct areas of the medial prefrontal cortex (MPFC) and the anterior cingulate cortex (ACC) during continuous real and sham tVNS; 2) compared with sham tVNS, real tVNS increased the FC between the left NAc and bilateral MPFC/rACC in the slow-5 band (0.008-0.027) and between the right NAc and left insula, occipital gyrus, and right lingual/fusiform gyrum in the typical low band (0.008-0.09); and 3) the FC of the NAc-MPFC/rACC during real tVNS showed a negative association with Hamilton Depression Rating Scale (HAMD) score changes in the real tVNS group after one month of treatment, but not in the sham group. Our findings demonstrate that tVNS can modulate low frequency intrinsic FC among key brain regions involved in reward and motivation processing and provide insights into the brain mechanism underlying tVNS treatment of MDD.

The Heart´s rhythm 'n' blues: Sex differences in circadian variation patterns of vagal activity vary by depressive symptoms in predominantly healthy employees

INTRODUCTION

Successful regulation of emotional states is positively associated to mental health, while difficulties in regulating emotions are negatively associated to overall mental health and in particular associated with anxiety or depression symptoms. A key structure associated to socio-emotional regulatory processes is the central autonomic network. Activity in this structure is associated to vagal activity can be indexed noninvasively and simply by measures of peripheral cardiac autonomic modulations such as heart rate variability. Vagal activity exhibits a circadian variation pattern, with a maximum during nighttime. Depression is known to affect chronobiology. Also, depressive symptoms are known to be associated with decreased resting state vagal activity, but studies investigating the association between circadian variation pattern of vagal activity and depressive symptoms are scarce. We aim to examine these patterns in association to symptom severity of depression using chronobiologic methods.

METHODS

Data from the Manheim Industrial Cohort Studies (MICS) were used. A total of 3,030 predominantly healthy working adults underwent, among others, ambulatory 24-h hear rate-recordings, detailed health examination and online questionnaires and were available for this analysis. The root mean sum of successive differences (RMSSD) was used as an indicator of vagally mediated heart rate variability. Three individual-level cosine function parameters (MESOR, amplitude, acrophase) were estimated to quantify circadian variation pattern. Multivariate linear regression models including important covariates such as age, sex, and lifestyle factors as well as an interaction effect of sex with depressive symptoms were used to estimate the association of circadian variation pattern of vagal activity with depressive symptoms simultaneously.

RESULTS

The analysis sample consisted of 20.2% females and an average age 41 with standard deviation of 11 years. Nonparametric bivariate analysis revealed significant MESOR and amplitude differences between the 90^th percentile split, but not on acrophase. Multivariate linear regression models estimated depressive symptoms to be negatively associated with the 24h mean (MESOR) and oscillation amplitude in men but positively associated in women. This pattern of findings indicates a blunted day-night rhythm of vagal activity in men with greater depressive symptoms as well as a moderation effect of sex in the association of CVP and depressive symptoms.

CONCLUSIONS

This is the first study investigating circadian variation pattern by mild depressive symptoms in a large, rather healthy occupational sample. Depressive symptoms were associated with decreased circadian variation pattern of vagal activity in men but with increased circadian variation pattern in women. The possible underlying mechanism(s) are discussed using the neurovisceral integration model. These findings may have implications for the knowledge on etiology, diagnosis, course, and treatment of depressive symptoms and thus may be of significant public health relevance.

Enhancing treatment of osteoarthritis knee pain by boosting expectancy: A functional neuroimaging study

Objectives

Expectation can significantly modulate pain and treatment effects. This study aims to investigate if boosting patients' expectancy can enhance the treatment of knee osteoarthritis (KOA), and its underlying brain mechanism.

Methods

Seventy-four KOA patients were recruited and randomized to three groups: boosted acupuncture (with a manipulation to enhance expectation), standard acupuncture, or treatment as usual (TAU). Each patient underwent six treatments before being debriefed, and four additional treatments after being debriefed. The fMRI scans were applied during the first and sixth treatment sessions.

Results

We found significantly decreased knee pain in the boosted acupuncture group compared to the standard acupuncture or TAU groups after both six and ten treatments. Resting state functional connectivity (rsFC) analyses using the nucleus accumbens (NAc) as the seed showed rsFC increases between the NAc and the medial prefrontal cortex (MPFC)/rostral anterior cingulate cortex (rACC) and dorsolateral prefrontal cortex in the boosted group as compared to the standard acupuncture group after multiple treatments. Expectancy scores after the first treatment were significantly associated with increased NAc-rACC/MPFC rsFC and decreased knee pain following treatment.

Conclusions

Our study provides a novel method and mechanism for boosting the treatment of pain in patients with KOA. Our findings may shed light on enhancing outcomes of pharmacological and integrative medicines in clinical settings.

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Acupuncture with enhanced expectancy produced greater pain relief in KOA patients.

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NAc – ACC/MPFC rsFC increased after acupuncture with enhanced expectancy.

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NAc – ACC/MPFC rsFC increases are associated with clinical improvements.

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Our findings provide a novel method for boosting the treatment of chronic pain.

Treating Depression with Transcutaneous Auricular Vagus Nerve Stimulation: State of the Art and Future Perspectives

Depression is a highly prevalent disorder, and its treatment is far from satisfactory. There is an urgent need to develop a new treatment for depression. Although still at its early stage, transcutaneous auricular vagus nerve stimulation (taVNS) has shown promising potential for treating depression. In this article, we first summarize the results of clinical studies on the treatment effect of taVNS on depression. Then, we re-analyze a previous study to identify the specific symptoms taVNS can relieve as indicated by subscores of the 24-item Hamilton Depression Scale in patients with depression. We found that taVNS can significantly reduce multiple symptoms of depression patients, including anxiety, psychomotor retardation, sleep disturbance, and hopelessness. Next, we pose several hypotheses on the mechanism of taVNS treatment of depression, including directly and indirectly modulating the activity and connectivity of key brain regions involved in depression and mood regulation; inhibiting neuro-inflammatory sensitization; modulating hippocampal neurogenesis; and regulating the microbiome-brain-gut axis. Finally, we outline current challenges and lay out the future directions of taVNS treatment of depression, which include (1) intensively comparing stimulation parameters and "dose effect" (treatment frequency and duration) to maximize the treatment effect of taVNS; (2) exploring the effect of taVNS on disorders comorbid with depression (such as chronic pain disorders, cardiovascular disorder, and autism) to provide new "two-for-one" treatment approaches for patients with these disorders; and (3) applying multiple scale methods to explore the underlying mechanism of taVNS.

A distinct biomarker of continuous transcutaneous vagus nerve stimulation treatment in major depressive disorder

BACKGROUND

Major depression is the fourth leading cause of disability worldwide and poses a socioeconomic burden worldwide. Transcutaneous vagus nerve stimulation (tVNS) is a promising noninvasive clinical device that may reduce the severity of major depression. However, the neural mechanism underlying continuous tVNS has not yet been elucidated.

OBJECTIVE

We aimed to explore the effect of hypothalamic subregion functional connectivity (FC) changes during continuous tVNS treatment on major depressive disorder (MDD) patients and to identify the potential biomarkers for treatment outcomes.

METHODS

Forty-one mild to moderate MDD patients were recruited and received either real or sham tVNS treatment for 4 weeks. We used a seed-to-whole brain approach to estimate the FC changes of hypothalamic subregions and their surrounding control areas during continuous tVNS treatment and explored their association with clinical outcome changes after 4 weeks of treatment.

RESULTS

Of the thirty-six patients that completed the study, those in the tVNS group had significantly lower scores on the 24-item Hamilton Depression (HAM-D) Rating Scale compared to the sham tVNS group after 4 weeks of treatment. The FC between the bilateral medial hypothalamus (MH) and rostral anterior cingulate cortex (rACC) was significantly decreased during tVNS but not during sham tVNS. The strength of this FC was significantly correlated with HAM-D improvements after 4 weeks of tVNS.

CONCLUSION

The FC between the bilateral MH and rACC may serve as a potential biomarker for the tVNS state and predict treatment responses. Our results provide insights into the neural modulation mechanisms of continuous tVNS and reveal a potential therapeutic target for MDD patients.

Vagal Nerve Stimulation for Treatment-Resistant Depression

Major depressive disorder (MDD) is prevalent. Although standards antidepressants are more effective than placebo, up to 35% of patients do not respond to 4 or more conventional treatments and are considered to have treatment-resistant depression (TRD). Considerable effort has been devoted to trying to find effective treatments for TRD. This review focuses on vagus nerve stimulation (VNS), approved for TRD in 2005 by the Food and Drugs Administration. Stimulation is carried by bipolar electrodes on the left cervical vagus nerve, which are attached to an implanted stimulator generator. The vagus bundle contains about 80% of afferent fibers terminating in the medulla, from which there are projections to many areas of brain, including the limbic forebrain. Various types of brain imaging studies reveal widespread functional effects in brain after either acute or chronic VNS. Although more randomized control trials of VNS need to be carried out before a definitive conclusion can be reached about its efficacy, the results of open studies, carried out over period of 1 to 2 years, show much more efficacy when compared with results from treatment as usual studies. There is an increase in clinical response to VNS between 3 and 12 months, which is quite different from that seen with standard antidepressant treatment of MDD. Preclinically, VNS affects many of the same brain areas, neurotransmitters (serotonin, norepinephrine) and signal transduction mechanisms (brain-derived neurotrophic factor-tropomyosin receptor kinase B) as those found with traditional antidepressants. Nevertheless, the mechanisms by which VNS benefits patients nonresponsive to conventional antidepressants is unclear, with further research needed to clarify this.

Do the psychological effects of vagus nerve stimulation partially mediate vagal pain modulation?

There is preclinical and clinical evidence that vagus nerve stimulation modulates both pain and mood state. Mechanistic studies show brainstem circuitry involved in pain modulation by vagus nerve stimulation, but little is known about possible indirect descending effects of altered mood state on pain perception. This possibility is important, since previous studies have shown that mood state affects pain, particularly the affective dimension (pain unpleasantness). To date, human studies investigating the effects of vagus nerve stimulation on pain perception have not reliably measured psychological factors to determine their role in altered pain perception elicited by vagus nerve stimulation. Thus, it remains unclear how much of a role psychological factors play in vagal pain modulation. Here, we present a rationale for including psychological measures in future vagus nerve stimulation studies on pain.

The Role of Neural Plasticity in Depression: From Hippocampus to Prefrontal Cortex

Neural plasticity, a fundamental mechanism of neuronal adaptation, is disrupted in depression. The changes in neural plasticity induced by stress and other negative stimuli play a significant role in the onset and development of depression. Antidepressant treatments have also been found to exert their antidepressant effects through regulatory effects on neural plasticity. However, the detailed mechanisms of neural plasticity in depression still remain unclear. Therefore, in this review, we summarize the recent literature to elaborate the possible mechanistic role of neural plasticity in depression. Taken together, these findings may pave the way for future progress in neural plasticity studies.

Transcutaneous Vagus Nerve Stimulation: A Promising Method for Treatment of Autism Spectrum Disorders

Transcutaneous Vagus Nerve Stimulation (tVNS) on the auricular branch of the vagus nerve has been receiving attention due to its therapeutic potential for neuropsychiatric disorders. Although the mechanism of tVNS is not yet completely understood, studies have demonstrated the potential role of vagal afferent nerve stimulation in the regulation of mood and visceral state associated with social communication. In addition, a growing body of evidence shows that tVNS can activate the brain regions associated with Autism Spectrum Disorder (ASD), trigger neuroimmune modulation and produce treatment effects for comorbid disorders of ASD such as epilepsy and depression. We thus hypothesize that tVNS may be a promising treatment for ASD, not only for comorbid epilepsy and depression, but also for the core symptoms of ASD. The goal of this manuscript is to summarize the findings and rationales for applying tVNS to treat ASD and propose potential parameters for tVNS treatment of ASD.

Acupuncture treatment modulates the corticostriatal reward circuitry in major depressive disorder

Major depressive disorder (MDD) is a common disorder with a high prevalence and significant social and economic impacts. Nevertheless, the treatment of MDD is far from satisfactory. Acupuncture treatment has emerged as a promising method for treating MDD. However, the neural mechanism by which acupuncture reduces depressive symptoms is not fully understood. Studies have shown that the corticostriatal reward circuitry is associated with the pathophysiology of MDD; thus, we investigated the corticostriatal resting-state functional connectivity (rsFC) before and after real and sham acupuncture treatments combined with the antidepressant fluoxetine. Forty-six female major depressive patients were assigned to either verum acupuncture plus fluoxetine (n = 22) or sham acupuncture plus fluoxetine (n = 24) treatment for 8 weeks, and resting state functional magnetic resonance imaging (fMRI) data were collected before the first and after the last treatment sessions. The results showed that compared with sham acupuncture, the verum acupuncture group showed: (1) significantly increased rsFC between inferior ventral striatum and medial prefrontal cortex, ventral rostral putamen and amygdala/parahippocampus, as well as dorsal caudate and middle temporal gyrus; (2) significantly decreased rsFC between right ventral rostral putamen and right dorsolateral prefrontal cortex, and right dorsal caudate and bilateral cerebellar tonsil. The increased rsFC between the inferior ventral striatum and medial prefrontal cortex, ventral rostral putamen and amygdala/parahippocampus were significantly positively associated with decreased clinical scores (Montgomery-Åsberg Depression Rating Scale and Self-Rating Depression Scale scores) at the end of the eight-week treatment. Our findings suggest that acupuncture may achieve treatment effects by modulating the corticostriatal reward/motivation circuitry in MDD patients.

The potential role of vagus-nerve stimulation in the treatment of HIV-associated depression: a review of literature

Depression is the most common comorbidity and neuropsychiatric complication in HIV. Estimates suggest that the prevalence rate for depression among HIV-infected individuals is three times that of the general population. The association between HIV and clinical depression is complex; however, chronic activation of inflammatory mechanisms, which disrupt central nervous system (CNS) function, may contribute to this association. Disruptions in CNS function can result in cognitive disorders, social withdrawal, fatigue, apathy, psychomotor impairment, and sleep disturbances, which are common manifestations in depression and HIV alike. Interestingly, the parasympathetic system-associated vagus nerve (VN) has primary homeostatic properties that restore CNS function following a stress or inflammatory response. Unfortunately, about 30% of adults with HIV are resistant to standard psychotherapeutic and psychopharmacological treatments for depression, thus suggesting the need for alternative treatment approaches. VN stimulation (VNS) and its benefits as a treatment for depression have been well documented, but remain unexplored in the HIV population. Historically, VNS has been delivered using a surgically implanted device; however, transcutanous VNS (tVNS) with nonsurgical auricular technology is now available. Although it currently lacks Food and Drug Administration approval in the US, evidence suggests several advantages of tVNS, including a reduced side-effect profile when compared to standard treatments and comparable results to implantable VNS in treating depression. Therefore, tVNS could offer an alternative for managing depression in HIV via regulating CNS function; moreover, tVNS may be useful for treatment of other symptoms common in HIV. From this, implications for nursing research and practice are provided.

Early cortical biomarkers of longitudinal transcutaneous vagus nerve stimulation treatment success in depression

Transcutaneous vagus nerve stimulation (tVNS), a non-invasive method of brain stimulation through the auricular branch of the vagus nerve, has shown promising results in treating major depressive disorder (MDD) in several pilot studies. However, the neural mechanism by which the effect on depression might be achieved has not been fully investigated, with only a few neuroimaging studies demonstrating tVNS-induced changes in the brains of healthy volunteers. Identifying specific neural pathways, which are influenced by tVNS compared with sham in depressed individuals, as well as determining neurobiomarkers of tVNS treatment success are needed to advance the application of tVNS for MDD. In order to address these questions, we measured fMRI brain activity of thirty-eight depressed patients assigned to undergo tVNS (n = 17) or sham (n = 21) treatment for 4 weeks, during the first stimulation session. The results showed significant fMRI signal increases in the left anterior insula, revealed by a direct comparison of tVNS and sham stimulation. Importantly, the insula activation level during the first stimulation session in the tVNS group was significantly associated with the clinical improvement at the end of the four-week treatment, as indicated by the Hamilton Depression Rating Scale (HAM-D) score. Our findings suggest that anterior insula fMRI activity could serve as a potential cortical biomarker and an early predictor of tVNS longitudinal treatment success.

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Transcutaneous vagus nerve stimulation (tVNS) was used to treat depression (75).

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Significant fMRI activation in the left anterior insula was observed during tVNS (81).

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Insula activation during the first treatment was associated with clinical improvement (85).

Vagus nerve stimulation in psychiatry: a systematic review of the available evidence

Invasive and non-invasive vagus nerve stimulation (VNS) is a promising add-on treatment for treatment-refractory depression, but is also increasingly evaluated for its application in other psychiatric disorders, such as dementia, schizophrenia, somatoform disorder, and others. We performed a systematic review aiming to give a detailed overview of the available evidence of the efficacy of VNS for the treatment of psychiatric disorders. Data derived from animal models, experimental trials without health-related outcomes, case reports, single-session studies, and reviews were excluded. From 1292 publications, 33 records were included for further analyses: 25 focused on VNS as treatment of unipolar or bipolar major depressive disorder and one investigated the neurocognitive improvement after VNS in major depressive disorder. Seven focused on the improvement of cognitive function in Alzheimer´s disease, improvement of schizophrenia symptoms, treatment of obsessive compulsive disorder (OCD), panic disorder (PD) and post-traumatic stress disorder (PTSD), treatment resistant rapid-cycling bipolar disorder, treatment of fibromyalgia, and Prader-Willi syndrome. A total of 29 studies used invasive VNS, while four studies used non-invasive, transcutaneous VNS. Only 7 out of 33 studies investigated conditions other than affective disorders. The efficacy data of VNS in affective disorders is promising, whereas more in controlled and naturalistic studies are needed. In other conditions like schizophrenia, Alzheimer's disease, OCD, PD, PTSD, and fibromyalgia, either no effects or preliminary data on efficacy were reported. At this point, no final conclusion can be made regarding the efficacy of VNS to improve symptoms in psychiatric disorders other than in affective disorders.