“The Wandering Nerve Linking Heart and Mind” – The Complementary Role of Transcutaneous Vagus Nerve Stimulation in Modulating Neuro-Cardiovascular and Cognitive Performance

Vagus Nerve Stimulation for Improvement of Vascular Cognitive Impairment

Vagus nerve stimulation (VNS) is acknowledged as a highly effective therapy for various neurological conditions, including refractory epilepsy, depression, Alzheimer's disease (AD), migraine, and stroke. Presently, there is an increasing focus on understanding the impact of VNS on cognitive aspects. Numerous studies suggest that VNS suppresses the body's inflammatory response, leading to enhanced cognitive function in patients. Vascular cognitive impairment (VCI) is a severe cognitive dysfunction syndrome resulting from prolonged chronic cerebral hypoperfusion (CCH), where the primary pathogenesis is CCH-induced neuroinflammation. In this paper, we present a comprehensive overview of the research advancements in using VNS for treating VCI and discuss that VNS improves cognitive function in VCI patients by suppressing neuroinflammation, offering insights into a potential novel approach for addressing this condition.

Influence of a 2-week transcutaneous auricular vagus nerve stimulation on memory: findings from a randomized placebo controlled trial in non-clinical adults

PURPOSE

Memory plays an essential role in daily life and is one of the first functions to deteriorate in cognitive impairment and dementia. Transcutaneous vagus nerve stimulation (tVNS) is a promising therapeutic method; however, its ability to enhance memory is underexplored, especially considering long-term stimulation. We aimed to investigate the effect of a 2-week course of auricular tVNS (taVNS) on memory in a non-clinical population.

METHODS

This single-blind randomized placebo-wait-list controlled trial recruited 76 participants (30 men; mean age 48.32 years) and randomized them into four groups: early active/sham taVNS and late active/sham taVNS. Participation in the study lasted 4 weeks; early groups underwent 2 weeks intervention immediately following the first study site visit (days 0-13) and late groups 2 weeks after the first study site visit (days 14-27). Active and sham taVNS included 2 weeks of daily 4-h neurostimulation at the tragus or earlobe, respectively. To assess memory, we used the Rey Auditory Verbal Learning Test.

RESULTS

Two weeks of active taVNS, but not sham taVNS, improved immediate recall and short-term memory score both in early and late groups. Furthermore, the improvements persisted over subsequent follow-up in early active taVNS. Importantly, the effect of active taVNS was superior to sham for immediate recall in both early and late groups. There were no statistical differences in delayed recall.

CONCLUSION

Our findings suggest that taVNS has potential to improve memory, particularly immediate recall, and may be an effective method in preventing memory loss and mitigating cognitive aging.

Vagus Nerve Suppression in Ischemic Stroke by Carotid Artery Occlusion: Implications for Metabolic Regulation, Cognitive Function, and Gut Microbiome in a Gerbil Model

The vagus nerve regulates metabolic homeostasis and mediates gut-brain communication. We hypothesized that vagus nerve dysfunction, induced by truncated vagotomy (VGX) or carotid artery occlusion (AO), would disrupt gut-brain communication and exacerbate metabolic dysregulation, neuroinflammation, and cognitive impairment. This study aimed to test the hypothesis in gerbils fed a high-fat diet. The gerbils were divided into four groups: AO with VGX (AO_VGX), AO without VGX (AO_NVGX), no AO with VGX (NAO_VGX), and no AO without VGX (NAO_NVGX). After 5 weeks on a high-fat diet, the neuronal cell death, neurological severity, hippocampal lipids and inflammation, energy/glucose metabolism, intestinal morphology, and fecal microbiome composition were assessed. AO and VGX increased the neuronal cell death and neurological severity scores associated with increased hippocampal lipid profiles and lipid peroxidation, as well as changes in the inflammatory cytokine expression and brain-derived neurotrophic factor (BDNF) levels. AO and VGX also increased the body weight, visceral fat mass, and insulin resistance and decreased the skeletal muscle mass. The intestinal morphology and microbiome composition were altered, with an increase in the abundance of Bifidobacterium and a decrease in Akkermansia and Ruminococcus. Microbial metagenome functions were also impacted, including glutamatergic synaptic activity, glycogen synthesis, and amino acid biosynthesis. Interestingly, the effects of VGX were not significantly additive with AO, suggesting that AO inhibited the vagus nerve activity, partly offsetting the effects of VGX. In conclusion, AO and VGX exacerbated the dysregulation of energy, glucose, and lipid metabolism, neuroinflammation, and memory deficits, potentially through the modulation of the gut-brain axis. Targeting the gut-brain axis by inhibiting vagus nerve suppression represents a potential therapeutic strategy for ischemic stroke.

Analysis of taVNS effects on autonomic and central nervous systems in healthy young adults based on HRV, EEG parameters

Objective.Transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive method of stimulating the vagus nerve, simultaneously affects the autonomic nervous system (ANS) and central nervous system (CNS) through efferent and afferent pathways. The purpose of this study is to analyze the effect of taVNS on the ANS and CNS through heart rate variability (HRV) and electroencephalography (EEG) parameters of identified responders.Approach.Two sets of data were collected from each of 10 healthy adult male subjects in their 20 s, and five HRV parameters from the time domain (RMSSD, pNN50, pNN30, pNN20, ppNNx) and two EEG parameters (power of alpha band, power of delta band) were extracted.Main results.Based on pNN50, responders to taVNS were identified; among them, pNN50 (p= 0.0041) and ppNNx (p= 0.0037) showed significant differences before and after taVNS. At the same time, for alpha power and delta power of EEG, significant difference (p< 0.05) was observed in most channels after taVNS compared to before stimulation.Significance.This study demonstrated the validity of identifying responders using pNN50 and the influence of taVNS on both the ANS and CNS. We conclude that taVNS can be used to treat a variety of diseases and as a tool to help control the ANS and CNS.

State- and frequency-dependence in autonomic rebalance mediated by intradermal auricular electroacupuncture stimulation

Background

Vagus nerve stimulation (VNS) improves diseases such as refractory epilepsy and treatment-resistant depression, likely by rebalancing the autonomic nervous system (ANS). Intradermal auricular electro-acupuncture stimulation (iaES) produces similar effects. The aim of this study was to determine the effects of different iaES frequencies on the parasympathetic and sympathetic divisions in different states of ANS imbalance.

Methods

We measured heart rate variability (HRV) and heart rate (HR) of non-modeled (normal) rats with the treatment of various frequencies to determine the optimal iaES frequency. The optimized iaES frequency was then applied to ANS imbalance model rats to elucidate its effects.

Results

30 Hz and 100 Hz iaES clearly affected HRV and HR in normal rats. 30 Hz iaES increased HRV, and decreased HR. 100 Hz iaES decreased HRV, and increased HR. In sympathetic excited state rats, 30 Hz iaES increased HRV. 100 Hz iaES increased HRV, and decreased HR. In parasympathetic excited state rats, 30 Hz and 100 Hz iaES decreased HRV. In sympathetic inhibited state rats, 30 Hz iaES decreased HRV, while 100 Hz iaES decreased HR. In parasympathetic inhibited rats, 30 Hz iaES decreased HR and 100 Hz iaES increased HRV.

Conclusion

30 Hz and 100 Hz iaES contribute to ANS rebalance by increasing vagal and sympathetic activity with different amplifications. The 30 Hz iaES exhibited positive effects in all the imbalanced states. 100 Hz iaES suppressed the sympathetic arm in sympathetic excitation and sympathetic/parasympathetic inhibition and suppressed the vagal arm and promoted the sympathetic arm in parasympathetic excitation and normal states.

Long-term effects of vagus nerve stimulation therapy on cognitive functioning in patients with drug-resistant epilepsy

BACKGROUND

Despite the increasing use of vagus nerve stimulation (VNS) for drug-resistant epilepsy, its impact on cognitive functioning remains insufficiently investigated.

OBJECTIVE

We aimed to comprehensively assess changes in cognition after long-term VNS therapy in a prospective sample of adults with epilepsy.

METHODS

Between December 2019 and March 2023, patients scheduled for VNS implantation were invited for neuropsychological assessment, including tests of executive functions, working and short-term memory (recall of a verbal logical story and the Rey-Osterrieth complex figure (ROCF)), and social cognition. Participants were re-evaluated after a year of VNS therapy and the pre- and postoperative scores were compared by means of the Student's t or Wilcoxon's signed rank tests for paired samples. Patients available only after a longer follow-up (more than 24 months) were also re-examined and included in a secondary analysis.

RESULTS

The study included 28 PWE (16, 57.1% female, average age 33.7 ± 10.0 years). Twenty-two PWE followed-up at 14.5 ± 4.8 months had worse categorical verbal fluency than preoperatively (t = 2.613, p = 0.016). After including patients with long follow-up (n = 28, 21.6 ± 11.4 months), the group scored better on the delayed recall of the ROCF (17.09 ± 8.84 to 20.65 ± 8.32 points, t(22) =  - 2.618, p = 0.016) and the Happé strange stories test (5.0 ± 2.6 to 6.1 ± 2.1 points, t(14) =  - 3.281, p = 0.005). No significant changes were observed in other cognitive domains (p > 0.05).

CONCLUSION

We suggest improvements in a task of social cognition and short-term visual memory after longer use of VNS therapy. Such findings should be confirmed in larger trials after controlling for changes in ictal or interictal activity.

Transcutaneous vagus nerve stimulation: a new strategy for Alzheimer's disease intervention through the brain-gut-microbiota axis?

Transcutaneous vagus nerve stimulation (tVNS) is an emerging non-invasive technique designed to stimulate branches of the vagus nerve distributed over the body surface. Studies suggest a correlation between the brain-gut-microbiota (BGM) axis and the pathogenesis of Alzheimer's disease (AD). The BGM axis represents a complex bidirectional communication system, with the vagus nerve being a crucial component. Therefore, non-invasive electrical stimulation of the vagus nerve might have the potential to modify-most of the time probably in a non-physiological way-the signal transmission within the BGM axis, potentially influencing the progression or symptoms of AD. This review explores the interaction between percutaneous vagus nerve stimulation and the BGM axis, emphasizing its potential effects on AD. It examines various aspects, such as specific brain regions, gut microbiota composition, maintenance of intestinal environmental homeostasis, inflammatory responses, brain plasticity, and hypothalamic-pituitary-adrenal (HPA) axis regulation. The review suggests that tVNS could serve as an effective strategy to modulate the BGM axis and potentially intervene in the progression or treatment of Alzheimer's disease in the future.

Vagus Nerve Stimulation Therapy for Drug-Resistant Epilepsy in Children-A Literature Review

Vagus nerve stimulation (VNS) is a palliative treatment for drug-resistant epilepsy (DRE) that has been in use for over two decades. VNS suppresses epileptic seizures, prevents emotional disorders, and improves cognitive function and sleep quality, a parallel effect associated with the control of epileptic seizures. The seizure suppression rate with VNS increases monthly to annually, and the incidence of side effects reduces over time. This method is effective in treating DRE in children as well as adults, such as epilepsy associated with tuberous sclerosis, Dravet syndrome, and Lennox-Gastaut syndrome. In children, it has been reported that seizures decreased by >70% approximately 8 years after initiating VNS, and the 50% responder rate was reported to be approximately 70%. VNS regulates stimulation and has multiple useful systems, including self-seizure suppression using magnets, additional stimulation using an automatic seizure detection system, different stimulation settings for day and night, and an automatic stimulation adjustment system that reduces hospital visits. VNS suppresses seizures and has beneficial behavioral effects in children with DRE. This review describes the VNS system, the mechanism of the therapeutic effect, the specific stimulation adjustment method, antiepileptic effects, and other clinical effects in patients with childhood DRE.

Transcutaneous Vagus Nerve Stimulation (tVNS) applications in cognitive aging: a review and commentary

Differentiating healthy from pathological aging trajectories is extremely timely, as the global population faces an inversion where older adults will soon outnumber younger 5:1. Many cognitive functions (e.g., memory, executive functions, and processing speed) decline with age, a process that can begin as early as midlife, and which predicts subsequent diagnosis with dementia. Although dementia is a devastating and costly diagnosis, there remains limited evidence for medications, therapies, and devices that improve cognition or attenuate the transition into dementia. There is an urgent need to intervene early in neurodegenerative processes leading to dementia (e.g., depression and mild cognitive impairment). In this targeted review and commentary, we highlight transcutaneous Vagus Nerve Stimulation (tVNS) as a neurostimulation method with unique opportunities for applications in diseases of aging, reviewing recent literature, feasibility of use with remote data collection methods/telehealth, as well as limitations and conflicts in the literature. In particular, small sample sizes, uneven age distributions of participants, lack of standardized protocols, and oversampling of non-representative groups (e.g., older adults with no comorbid diagnoses) limit our understanding of the potential of this method. We offer recommendations for how to improve representativeness, statistical power, and generalizability of tVNS research by integrating remote data collection techniques.

Neuroimmunomodulation of vagus nerve stimulation and the therapeutic implications

Vagus nerve stimulation (VNS) is a technology that provides electrical stimulation to the cervical vagus nerve and can be applied in the treatment of a wide variety of neuropsychiatric and systemic diseases. VNS exerts its effect by stimulating vagal afferent and efferent fibers, which project upward to the brainstem nuclei and the relayed circuits and downward to the internal organs to influence the autonomic, neuroendocrine, and neuroimmunology systems. The neuroimmunomodulation effect of VNS is mediated through the cholinergic anti-inflammatory pathway that regulates immune cells and decreases pro-inflammatory cytokines. Traditional and non-invasive VNS have Food and Drug Administration (FDA)-approved indications for patients with drug-refractory epilepsy, treatment-refractory major depressive disorders, and headaches. The number of clinical trials and translational studies that explore the therapeutic potentials and mechanisms of VNS is increasing. In this review, we first introduced the anatomical and physiological bases of the vagus nerve and the immunomodulating functions of VNS. We covered studies that investigated the mechanisms of VNS and its therapeutic implications for a spectrum of brain disorders and systemic diseases in the context of neuroimmunomodulation.

Nonpharmacological modulation of cortical spreading depolarization

AIMS

Cortical spreading depolarization (CSD) is a wave of pathologic neuronal dysfunction that spreads through cerebral gray matter, causing neurologic disturbance in migraine and promoting lesion development in acute brain injury. Pharmacologic interventions have been found to be effective in migraine with aura, but their efficacy in acutely injured brains may be limited. This necessitates the assessment of possible adjunctive treatments, such as nonpharmacologic methods. This review aims to summarize currently available nonpharmacological techniques for modulating CSDs, present their mechanisms of action, and provide insight and future directions for CSD treatment.

MAIN METHODS

A systematic literature review was performed, generating 22 articles across 3 decades. Relevant data is broken down according to method of treatment.

KEY FINDINGS

Both pharmacologic and nonpharmacologic interventions can mitigate the pathological impact of CSDs via shared molecular mechanisms, including modulating K⁺/Ca²⁺/Na⁺/Cl^- ion channels and NMDA, GABA_A, serotonin, and CGRP ligand-based receptors and decreasing microglial activation. Preclinical evidence suggests that nonpharmacologic interventions, including neuromodulation, physical exercise, therapeutic hypothermia, and lifestyle changes can also target unique mechanisms, such as increasing adrenergic tone and myelination and modulating membrane fluidity, which may lend broader modulatory effects. Collectively, these mechanisms increase the electrical initiation threshold, increase CSD latency, slow CSD velocity, and decrease CSD amplitude and duration.

SIGNIFICANCE

Given the harmful consequences of CSDs, limitations of current pharmacological interventions to inhibit CSDs in acutely injured brains, and translational potentials of nonpharmacologic interventions to modulate CSDs, further assessment of nonpharmacologic modalities and their mechanisms to mitigate CSD-related neurologic dysfunction is warranted.