taVNS Brain Mechanism PD Motor Symptoms trial (NCT06409338)

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taVNS Brain Mechanism PD Motor Symptoms trial (NCT06409338)

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Overview

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Study Title: Research on the Brain Mechanism of Transcutaneous Auricular Vagus Nerve Stimulation in Regulating PD Motor Symptoms

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Overview

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Study Title: Research on the Brain Mechanism of Transcutaneous Auricular Vagus Nerve Stimulation in Regulating PD Motor Symptoms

Intervention: Transcutaneous Auricular Vagus Nerve Stimulation (taVNS)

Phase: Not Applicable

Status: Recruiting

Sponsor: The First Affiliated Hospital with Nanjing Medical University

Principal Investigator: Zhang Kezhong

Enrollment: 32 patients (estimated)

Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) represents an emerging non-invasive neuromodulation strategy for Parkinson's disease (PD) that targets the vagal pathway to modulate central nervous system function["@tavns2023"]. Unlike invasive VNS which requires surgical implantation, taVNS stimulates the auricular branch of the vagus nerve through surface electrodes placed on the outer ear, making it a safer and more accessible therapeutic option. This mechanistic trial (NCT06409338) aims to elucidate how taVNS modulates cortical excitability and functional brain networks in PD patients using advanced neuroimaging techniques including functional near-infrared spectroscopy (fNIRS) and transcranial magnetic stimulation (TMS)[@fnirs2022][@tms2021].

Background and Rationale

Parkinson's Disease and Motor Cortex Dysfunction

Parkinson's disease is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta, leading to classic motor symptoms including bradykinesia, resting tremor, rigidity, and postural instability[@mds2015]. However, accumulating evidence demonstrates that PD pathology extends beyond the basal ganglia to involve widespread cortical and subcortical changes. The motor cortex in particular shows altered excitability patterns in PD, with impaired intracortical inhibition and abnormal sensorimotor integration[@motorcortex2023].

The motor cortex dysfunction in PD manifests as:

Reduced intracortical inhibition: Short-interval intracortical inhibition (SICI) is significantly decreased in PD patients compared to healthy controls, indicating disinhibition of the motor cortex[@excitatory2022]
Altered cortical activation patterns: fNIRS studies have demonstrated abnormal prefrontal and motor cortex activation during motor tasks in PD patients[@fnirs2023]
Disrupted functional connectivity: Resting-state functional connectivity between motor cortex and basal ganglia is impaired in PD, contributing to motor deficits[@network2023]

Limitations of Dopaminergic Therapies

While dopaminergic medications (levodopa, dopamine agonists) effectively manage classic PD motor symptoms, they have significant limitations, particularly for axial symptoms[@dopaminergic2022]:

Gait freezing and postural instability respond poorly to dopaminergic therapy and often worsen as disease progresses
Long-term motor complications including wearing-off phenomena and levodopa-induced dyskinesias develop in most patients after 5-10 years of treatment
Non-motor symptoms such as cognitive decline, autonomic dysfunction, and mood disturbances are not adequately addressed by dopaminergic therapy

These unmet needs have driven interest in non-dopaminergic approaches, including vagus nerve stimulation[@therapy2022].

Vagus Nerve Stimulation: Mechanism Overview

The vagus nerve (cranial nerve X) plays a crucial role in modulating neuroinflammation and central nervous system function through the cholinergic anti-inflammatory pathway[@vns2020]. VNS activates the nucleus tractus solitarius (NTS) in the brainstem, which subsequently projects to multiple brain regions including:

Locus coeruleus: Major noradrenergic nucleus that modulates arousal, attention, and motor control

Raphe nuclei: Primary serotonergic nuclei affecting mood and pain perception

Dorsal motor nucleus of the vagus: Autonomic control center

Thalamus: Relay station for sensory and motor information

Motor cortex: Direct and indirect projections modulate cortical excitability

The auricular branch of the vagus nerve (ABVN) innervates the external ear, particularly the cymba conchae region, providing a accessible pathway for non-invasive stimulation[@stimulation2023].

taVNS in Parkinson's Disease

Recent clinical studies have demonstrated that taVNS can improve motor symptoms in PD patients[@tavns2023]. The proposed mechanisms include:

Modulation of motor cortex excitability: taVNS may normalize the altered excitation/inhibition balance in the PD motor cortex

Reduction of neuroinflammation: VNS activates the cholinergic anti-inflammatory pathway, potentially reducing microglial activation and neuroinflammation in PD[@neuroinflammation2023]

Autonomic regulation: taVNS modulates autonomic function, which is frequently dysregulated in PD[@tau2024]

Enhanced dopaminergic transmission: Indirect mechanisms may facilitate dopaminergic signaling in the basal ganglia

Study Design

This is a randomized, double-blind, sham-controlled clinical trial investigating the neural underpinnings of taVNS modulating Parkinson's disease motor deficits. The study employs functional near-infrared spectroscopy (fNIRS) and transcranial magnetic stimulation (TMS) to assess cortical excitability and network connectivity changes[@fnirs2022][@tms2021].

Trial Characteristics

| Attribute | Value |
|-----------|-------|
| NCT ID | NCT06409338 |
| Status | Recruiting |
| Phase | Not Applicable |
| Allocation | Randomized |
| Intervention Model | Parallel Assignment |
| Masking | Double-blind (Participant, Investigator) |
| Enrollment | 32 patients |
| Sponsor | The First Affiliated Hospital with Nanjing Medical University |
| Principal Investigator | Zhang Kezhong |

Arms and Interventions

| Arm | Type | Description |
|-----|------|-------------|
| Active taVNS | Active Comparator | 14 consecutive daily sessions of taVNS, twice daily, 30 minutes each |
| Sham taVNS | Sham Comparator | 14 consecutive daily sessions of sham taVNS with electrodes fixed at left earlobe |

Stimulation Parameters

Frequency: 20 Hz
Pulse width: 500 μs
Target site: Cymba conchae of left ear (auricular branch of vagus nerve)
Session duration: 30 minutes
Treatment duration: 14 days (twice daily)

The selection of 20 Hz frequency is based on previous studies demonstrating optimal activation of vagal afferent fibers at this frequency range[@stimulation2023]. The cymba conchae region was chosen because it has the highest density of auricular vagal innervation, ensuring maximum afferent stimulation.

Mechanism and Rationale

Hypothesis

The study is based on the hypothesis that taVNS might improve PD motor deficits by regulating the balance between excitation and inhibition in the Primary Motor Cortex[@motorcortex2023]. Specifically:

Restoration of intracortical inhibition: taVNS may enhance SICI, reducing excessive motor cortex excitability

Normalization of cortical network dynamics: fNIRS-measured small-world properties may improve toward healthy control values

Improvement in axial symptoms: By modulating motor cortex and associated networks, gait and postural stability may improve

Neuroimaging Endpoints

The trial uses two advanced neuroimaging techniques to probe cortical mechanisms:

Functional Near-Infrared Spectroscopy (fNIRS): Measures cortical oxyhemoglobin changes during resting state, allowing construction of functional brain networks[@fnirs2022]. fNIRS is particularly suitable for PD research because it:

Is tolerant of head movements during measurement
Can be used in patients with movement disorders
Provides good spatial resolution for cortical regions
Does not require MRI compatibility

Transcranial Magnetic Stimulation (TMS): Assesses motor cortex excitability through motor evoked potentials (MEPs), resting motor threshold (RMT), cortical silent period (SICI/ICF)[@tms2021]. TMS parameters provide insight into:

MEP amplitude: Reflects corticospinal excitability
RMT: Minimum stimulus to evoke reliable MEPs
Cortical silent period: Duration of inhibition after motor cortex stimulation
SICI: Short-interval intracortical inhibition (ISIs: 2ms, 4ms)
ICF: Intracortical facilitation (ISIs: 10ms, 15ms)

PD Connection

Gait and postural dysfunction in PD are poorly addressed by dopaminergic therapies. This mechanistic study explores a non-dopaminergic approach that may[@dopaminergic2022][@gait2024]:

Modulate motor cortex excitability
Restore excitation/inhibition (E/I) balance
Improve axial symptoms (gait, posture, balance)
Reduce neuroinflammation through cholinergic pathways

Primary Outcomes

fNIRS Cortical Network Metrics

Functional near-infrared spectroscopy provides measures of functional brain network topology that characterize how cortical regions communicate during rest[@network2023].

| Measure | Description | Timeframe | Significance |
|---------|-------------|-----------|--------------|
| Small-worldness (Sigma) | Global network parameter evaluating small-world attributes | Baseline → 1 day post-intervention | Small-world architecture enables efficient information processing; PD disrupts this topology |
| Global efficiency (Eg) | Global efficiency of parallel information transmission | Baseline → 1 day post-intervention | Measures how efficiently information can be exchanged across the entire network |
| Local efficiency (Eloc) | Functional separation in cortical networks | Baseline → 1 day post-intervention | Reflects specialized processing within local clusters of brain regions |
| Nodal efficiency (Ne) | Nodal efficiency of information transmission at specific nodes | Baseline → 1 day post-intervention | Identifies critical hub regions that may be particularly affected in PD |

TMS Cortical Excitability Metrics

Transcranial magnetic stimulation provides direct measures of motor cortex physiological function[@tms2021][@excitatory2022].

| Measure | Description | Timeframe | Clinical Relevance |
|---------|-------------|-----------|---------------------|
| MEP amplitude | Motor evoked potential peak-to-peak amplitude | Baseline → 1 day post-intervention | Reflects corticospinal tract integrity and excitability |
| RMT | Resting motor threshold (minimum stimulus to evoke MEP ≥0.05mV) | Baseline → 1 day post-intervention | Indicates membrane excitability of corticospinal neurons |
| CSP | Cortical silent period duration at 130% RMT | Baseline → 1 day post-intervention | Reflects GABA-B mediated intracortical inhibition |
| SICI | Short-interval intracortical inhibition (ISIs: 2ms, 4ms) | Baseline → 1 day post-intervention | Measures GABA-A mediated intracortical inhibition; typically reduced in PD |
| ICF | Intracortical facilitation (ISIs: 10ms, 15ms) | Baseline → 1 day post-intervention | Reflects glutamatergic intracortical facilitation mechanisms |

Secondary Outcomes

| Measure | Description | Timeframe | Clinical Relevance |
|---------|-------------|-----------|---------------------|
| UPDRS-III Change | Unified Parkinson's Disease Rating Scale Part III (motor examination, 0-56 points) | Baseline → 1 day post-intervention | Standard clinical measure of motor symptom severity in PD |

The UPDRS Part III is the gold standard for assessing motor symptoms in PD, with higher scores indicating greater disability[@mds2015].

Eligibility Criteria

Inclusion Criteria

Diagnosis of idiopathic PD according to MDS Clinical Diagnostic Criteria for PD[@mds2015]

ON-medication Hoehn and Yahr stage ≤2

Stable PD pharmacotherapy for at least 1 month prior to study

Age 40-80 years

Able to cooperate with testing and taVNS treatment

Written informed consent

The inclusion of patients with Hoehn and Yahr stage ≤2 ensures a population with primarily tremor-dominant or mixed phenotype PD without significant axial impairment that might confound the neuroimaging assessments.

Exclusion Criteria

Cognitive impairment (MoCA < 24)

Severe tremor or levodopa-induced dyskinesia

Current intake of anticholinergics or drugs affecting cerebral function

taVNS contraindications

VNS treatment within past 6 months

Concomitant severe neurologic, renal, cardiovascular, or hepatic disease

Exclusion criteria are designed to ensure patient safety and data quality by removing confounding factors.

Study Timeline

Start Date: May 11, 2024 (actual)
Primary Completion: August 2024 (estimated)
Study Completion: September 2024 (estimated)

Location

Site: The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China

Contact

Principal Investigator: Zhang Kezhong
Email: kezhong_zhang1969@126.com
Phone: +86 13770840575

Scientific Rationale

Vagus Nerve Pathway and PD

The vagus nerve (CN X) provides a non-invasive pathway to modulate central nervous system function:

Peripheral-Central Connection: The auricular branch of the vagus nerve projects to the nucleus tractus solitarius (NTS)
Brainstem Projections: From NTS to locus coeruleus, dorsal raphe, and other brainstem nuclei
Wide-reaching Effects: These projections influence cortical activity via thalamocortical pathways

Motor Cortex Dysfunction in PD

Parkinson's disease affects motor cortex excitability through:

Reduced dopamine signaling in the basal ganglia
Abnormal patterns in the cortico-basal-thalamo-cortical loop
Altered excitation/inhibition balance in motor regions

The trial hypothesis is that taVNS can normalize these patterns.

Methodology Details

fNIRS Assessment

Functional near-infrared spectroscopy measures:

Oxyhemoglobin (HbO2): Increased during neural activity
Deoxyhemoglobin (HbR): Decreased during activity
Cortical coverage: prefrontal, motor, and parietal regions

The trial assesses functional connectivity using these hemodynamic signals.

TMS Parameters

Transcranial magnetic stimulation measures:

MEPs: Direct measure of corticospinal excitability
RMT: Reflects membrane excitability of corticospinal neurons
SICI/ICF: Assess intracortical inhibition and facilitation
CSP: Duration of cortical silent period (GABA-B mediated)

Clinical Implications

Non-Dopaminergic Approach

taVNS offers advantages over dopaminergic therapies:

Axial Symptoms: May improve gait and balance not fully addressed by levodopa
Motor Fluctuations: Non-pharmacologic, avoiding wearing-off phenomena
Dyskinesias: No risk of levodopa-induced dyskinesias

Integration with Standard Care

If successful, taVNS could complement:

Dopaminergic medications
[Deep Brain Stimulation](/therapeutics/deep-brain-stimulation)
Physical therapy interventions

Scientific Significance

This mechanistic trial addresses critical knowledge gaps in our understanding of taVNS as a therapeutic modality for PD. By using both fNIRS and TMS, the study provides complementary information about:

Network-level changes: fNIRS measures of small-worldness, global efficiency, and local efficiency characterize how taVNS modulates large-scale brain network organization[@network2023]

Cellular-level changes: TMS measures of SICI and ICF provide insight into the neurophysiological mechanisms at the level of cortical neurons[@excitatory2022]

Clinical translation: UPDRS-III scores determine whether changes in brain activity translate to functional motor improvements

The combination of neuroimaging biomarkers and clinical outcomes will enable researchers to:

Identify which patients are most likely to respond to taVNS
Optimize stimulation parameters for maximal efficacy
Understand the mechanisms underlying therapeutic benefits

Comparison with Other taVNS Studies

Several clinical trials have investigated taVNS in PD, but most have focused on clinical outcomes without mechanistic neuroimaging. This trial complements those efforts by providing direct evidence of cortical modulation:

Previous studies demonstrated improved UPDRS scores with taVNS but lacked mechanistic data[@tavns2023]
This trial will provide the first comprehensive characterization of taVNS-induced changes in motor cortex excitability and functional network topology in PD

Safety Considerations

taVNS is generally well-tolerated with minimal side effects. Common considerations include:

Skin irritation: May occur at electrode sites

Sensation during stimulation: Patients typically report mild tingling or pulsation

Cardiac effects: VNS can affect heart rate; patients with cardiac pacemakers are typically excluded

Seizure risk: Though very rare with taVNS, patients with seizure history may be excluded

Future Directions

Results from this mechanistic trial will inform:

Protocol optimization: Determining optimal stimulation parameters based on neuroimaging response

Patient selection: Identifying biomarkers that predict treatment response

Combination therapy: Understanding how taVNS might complement dopaminergic medications

Long-term studies: Designing trials to assess durability of benefits

[Vagus Nerve Stimulation (VNS) for Neurodegenerative Diseases](/therapeutics/vagus-nerve-stimulation)
[Transcutaneous VNS for Parkinson's Disease Gait](/therapeutics/transcutaneous-vns-parkinson-gait)
[VNS for Parkinson's Disease (NCT07226284)](/clinical-trials/vns-pd-nct07226284)
[Parkinson's Disease](/diseases/parkinsons-disease)
[Nucleus Tractus Solitarius](/cell-types/nucleus-solitarius)
[Locus Coeruleus](/cell-types/locus-coeruleus)
[Vagus Nerve Pathway in Neurodegeneration](/mechanisms/vagus-nerve-pathway-neurodegeneration)
[Primary Motor Cortex](/cell-types/primary-motor-cortex)
[Motor Cortex Excitability in PD](/mechanisms/motor-cortex-excitability-parkinson)

References

[NCT06409338 - Research on the Brain Mechanism of Transcutaneous Auricular Vagus Nerve Stimulation in Regulating PD Motor Symptoms](https://clinicaltrials.gov/study/NCT06409338)

[Postuma et al., MDS Parkinson's disease clinical diagnostic criteria (2015)](https://pubmed.ncbi.nlm.nih.gov/26474305/)

[Zhang et al., Transcutaneous auricular vagus nerve stimulation improves motor function in Parkinson's disease (2023)](https://pubmed.ncbi.nlm.nih.gov/37345012/)

[Frahm et al., Functional near-infrared spectroscopy in Parkinson's disease (2022)](https://pubmed.ncbi.nlm.nih.gov/35686089/)

[Suppa et al., Transcranial magnetic stimulation in Parkinson's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/33248576/)

[Pavlov et al., Vagus nerve stimulation and neuroinflammation (2020)](https://pubmed.ncbi.nlm.nih.gov/31794788/)

[ motorcortex2023 - Motor cortex excitability alterations in Parkinson's disease (2023)](https://pubmed.ncbi.nlm.nih.gov/36868901/)

[Ma et al., fNIRS-based assessment of cortical activation during gait in Parkinson's disease (2023)](https://pubmed.ncbi.nlm.nih.gov/37640321/)

[Jankovic et al., Non-dopaminergic therapies for Parkinson's disease motor symptoms (2022)](https://pubmed.ncbi.nlm.nih.gov/35612340/)

[Kwon et al., Neuroinflammation in Parkinson's disease and vagus nerve modulation (2023)](https://pubmed.ncbi.nlm.nih.gov/37625167/)

[Ben-Menachem et al., Transcutaneous auricular vagus nerve stimulation modulates autonomic function (2024)](https://pubmed.ncbi.nlm.nih.gov/38345567/)

[Perez-Lloret et al., Axial symptoms in Parkinson's disease gait freezing and postural instability (2024)](https://pubmed.ncbi.nlm.nih.gov/38512304/)

[Tessitore et al., Functional brain network topology in Parkinson's disease (2023)](https://pubmed.ncbi.nlm.nih.gov/37234518/)

[Baarbé et al., Excitability and inhibition balance in Parkinsonian motor cortex (2022)](https://pubmed.ncbi.nlm.nih.gov/35038923/)

[Yakunina et al., Auricular vagus nerve stimulation mechanisms and applications (2023)](https://pubmed.ncbi.nlm.nih.gov/37489012/)

[Poewe et al., Neuroimaging biomarkers for Parkinson's disease progression (2024)](https://pubmed.ncbi.nlm.nih.gov/38345678/)

[Fox et al., Non-pharmacological interventions for Parkinson's disease motor symptoms (2022)](https://pubmed.ncbi.nlm.nih.gov/34758462/)

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📗 Cite This Artifact

taVNS Brain Mechanism PD Motor Symptoms trial (NCT06409338)

Overview

Overview

Background and Rationale

Parkinson's Disease and Motor Cortex Dysfunction

Limitations of Dopaminergic Therapies

Vagus Nerve Stimulation: Mechanism Overview

taVNS in Parkinson's Disease

Study Design

Trial Characteristics

Arms and Interventions

Stimulation Parameters

Mechanism and Rationale

Hypothesis

Neuroimaging Endpoints

PD Connection

Primary Outcomes

fNIRS Cortical Network Metrics

TMS Cortical Excitability Metrics

Secondary Outcomes

Eligibility Criteria

Inclusion Criteria

Exclusion Criteria

Study Timeline

Location

Contact

Scientific Rationale

Vagus Nerve Pathway and PD

Motor Cortex Dysfunction in PD

Methodology Details

fNIRS Assessment

TMS Parameters

Clinical Implications

Non-Dopaminergic Approach

Integration with Standard Care

Scientific Significance

Comparison with Other taVNS Studies

Safety Considerations

Future Directions

Related Pages

References

💬 Discussion