Investigating the Neurophysiology of the Motor System and the Feasibility of Vagus Nerve Stimulation in Functional Neurological Disorder (FND) (TMS-VNS)

Investigating the Neurophysiology of the Motor System and the Feasibility of Vagus Nerve Stimulation in Functional Neurological Disorder (FND): a Randomized, Sham-controlled Study

This clinical study will test if adding a non-invasive stimulation of the vagus nerve through the ear during physiotherapy brings an improvement to FND (Functional Neurological Disorder) patients with motor symptoms.

First, the investigators will test the normal functioning of the motor regions of the brain in FND patients and in healthy volunteers for comparison, using a painless method called TMS (Transcranial Magnetic Stimulation). Then, the investigators will further test how brain regions communicate with each other in FND patients, using fMRI (functional Magnetic Resonance Imaging, also painless). Additionally, the investigators will ask both FND patients and healthy volunteers to answer questions about their health and wellbeing, and will assess the exact symptoms of FND patients. The FND patients will then be assigned to two groups randomly, and neither they nor the researchers will know in which group they are. Both groups will do 5 sessions of their usual physiotherapy - one group with a real stimulation of the vagus nerve, and the other group with a fake stimulation. This is important to obtain reliable results. At the end, both groups of patients will be tested again to see if the way brain regions communicate with each other has changed. They will also answer again questions about their health and wellbeing, and their symptoms will be assessed again, to see if any changes happen. The results of the two groups of patients will be compared to isolate the effects of vagus nerve stimulation from the effects of physiotherapy alone.

Study Overview

• Status: Not yet recruiting
• Conditions: Functional Neurological Disorder; Motor Symptoms
• Intervention / Treatment: Device: Vagial Nerve Stimulation (VNS) active stimulation; Device: Vagial Nerve Stimulation (VNS) sham stimulation

Detailed Description

The main goal of this project is to better understand the neurophysiology of the motor system and the role of attention in Functional Neurological Disorder (FND) and to explore the physiological effects of a novel non-invasive treatment option for this disorder.

To this end, several methods will be employed: non-invasive brain stimulation (using Transcranial Magnetic Stimulation, TMS), neuroimaging (fMRI), transdermal auricular vagus nerve stimulation (taVNS), clinical assessments and questionnaires.

The study consists of 2 experiments, each with specific objectives.

Primary objective:

The primary objective of this study is to assess the effects of taVNS, as an adjunctive intervention to standard physical therapy, on the quality of life in FND patients.

Secondary objectives:

Experiment 1

1. Assess baseline neurophysiological differences of the motor system at rest and under different attentional demands, between FND patients and healthy participants.
2. Compare the motor behaviour of the upper limb (index finger) under different attentional demands, in FND patients and healthy participants.
3. Explore the role of symptom severity, mood, physical health, and interoception (the perception of bodily signals), assessed by questionnaires, in the modulation of motor system neurophysiology in FND patients and healthy participants.
4. Explore the relationship between neurophysiological (point 1) and behavioral (point 2) outcomes, and the outcomes of clinical and psychological scores measured (point 3).

Experiment 2

1. Assess the feasibility of the taVNS intervention as an adjunctive treatment in FND.
2. Determine whether adding taVNS to standard physical therapy improves clinical outcomes (motor symptoms) in FND patients, assessed by clinical scores (CGI, sFMDRS).
3. Explore changes in self-reported measures of mood, stress, physical health and interoception (the perception of bodily signals), assessed by questionnaires, after taVNS in FND patients.
4. Explore changes in upper limb strength, measured by a grip strength test with hand-held dynamometer under different starting conditions (pressing freely and pressing after a cue), before, during and after taVNS in FND.
5. Assess the effect of taVNS on heart rate and heart rate variability (HRV) in FND patients.
6. Analyse the modulation of brain network connectivity via fMRI at rest and during a behavioural task (emotion-motion task), before and after taVNS in FND patients.
7. Explore the relationship between neuroimaging (point 6), behavioral (point 2) outcomes, and the outcomes of clinical and psychological scores measured (point 3).

An additional outcome will explore the relationship between the outcomes of Experiment 1 and Experiment 2 to assess the prognostic potential of the outcomes of Experiment 1.

• Study Type: Interventional
• Enrollment (Estimated): 68
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Michael Mouthon, PhD; Phone Number: +41 26 300 85 39; Email: michael.mouthon@unifr.ch
• Study Contact Backup: Name: Selma Aybek, Professor; Phone Number: +41 26 306 38 02; Email: selma.aybek@unifr.ch

Study Locations

• Switzerland
  • Canton of Fribourg
    • Fribourg, Canton of Fribourg, Switzerland, 1700
      • University of Fribourg
      • Contact: Michael Mouthon, PhD; Phone Number: +41 26 300 85 39; Email: michael.mouthon@unifr.ch
      • Sub-Investigator: Michael Mouthon, PhD
      • Contact: Selma Aybek, Professor; Phone Number: +41 26 306 38 02; Email: selma.aybek@unifr.ch
      • Sub-Investigator: Cristina Concetti, PhD
      • Sub-Investigator: Julia Paratte, Master
      • Sub-Investigator: Janne Magnin, Bachelor
      • Sub-Investigator: Sarah Botman, Bachelor

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria for FND patients:

• Over 18 years of age.
• Capable of judgement.
• Willing to participate in the study (by signing the informed consent form).
• FND diagnosis by a certified neurologist or psychiatrist.
• Motor FND symptoms in the upper limb in the form of tremor or weakness.
• Participating in physiotherapy for FND.

Exclusion Criteria for FND patients:

• Severe neuropsychiatric comorbidities.
• Pregnancy or breastfeeding.
• Prior knowledge on the effects of attention on the motor system.
• Prior history of epilepsy or epileptic seizures in the person and their family.
• Severe claustrophobia.
• Implanted medical devices.
• Ear anatomy incompatible with the taVNS device (e.g. cauliflower ear).
• Previous use of taVNS.
• Substance abuse.
• Simultaneous participation in another investigation involving an investigational drug or a MD.
• Enrolment of the PI and their dependent persons.

Inclusion Criteria for healthy volunteers:

• Over 18 years of age.
• Capable of judgement.
• Willing to participate in the study (by signing the informed consent form).

Exclusion Criteria for healthy volunteers:

• Neurological or neuropsychiatric or movement disorders.
• Pregnancy or breastfeeding.
• Prior knowledge on the effects of attention on the motor system.
• Prior history of epilepsy or epileptic seizures in the person and their family.
• Substance abuse.
• Simultaneous participation in another investigation involving an investigational drug or a MD.
• Enrolment of the PI and their dependent persons.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Supportive Care
• Allocation: Randomized
• Interventional Model: Factorial Assignment
• Masking: Double

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Patient VNS stimulation intervention; FND patients received a 30 minutes VNS stimulation for 5 sessions during their usual physiotherapy course treatment.	Device: Vagial Nerve Stimulation (VNS) active stimulation; taVNS sends gentle electric stimuli to the vagus nerve branch located in the outer ear, which are transmitted to the nucleus of the solitary tract in the brainstem, and from there to the rest of the brain. The electrode site is the cymba conchae in in the outer ear. VNS thus acts to enhance the activity of the parasympathetic nervous system.; Other Names: active; taVNS; tVNS
Sham Comparator: Patient VNS sham intervention; FND patients received a 30 minutes VNS sham for 5 sessions during their usual physiotherapy course treatment.	Device: Vagial Nerve Stimulation (VNS) sham stimulation; taVNS sends gentle electric stimuli for several minutes, during which time the patient will feel a tickling sensation. Then, for the rest of the session, the hidden device will be switched off (there will be no stimulation).; Other Names: sham; taVNS; tVNS
No Intervention: Heathy control without intervention

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Self-reported quality of life	The change in self-reported quality of life, measured through intervention sessions with the Euro Quality of Life questionnaire (EQ-5D-5L), compared between the active stimulation group and the sham stimulation group. This questionnaire includes 5 subscales (1-best, 5-worstest) about mobility, self-care, usual activities, pain/discomfort, anxiety/depression. In addition it includes a continue scale evaluation (0-worst to 100-best) about the patient evaluation on his health.	For each intervention session at weeks 3, 4, 5, 6, 7

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Neurophysiology investigation of the pathology by comparing Motor-Evoked Potential between FND patients and healthy participant	The study will examine cortical inhibition as measured by motor-evoked potentials (MEPs) during a short-interval intracortical inhibition (SICI) transcranial magnetic stimulation (TMS) protocol (single-pulse and paired-pulse). The investigators will examine how the outcome differs under different attentional demands in patients with functional neurological disorder (FND) and healthy participants.	At TMS session, week 2 for patients and week 0 for heathy controls
Neurophysiology investigation of the pathology by comparing resting motor threshold between FND patients and healthy participant	The study will examine the resting motor threshold (in millivolts), which is the level of stimulation required to trigger motor-evoked potentials using a single-pulse transcranial magnetic stimulation (TMS) technique. The investigators will examine how this outcome differs between patients with functional neurological disorder (FND) and healthy participants.	At TMS session, week 2 for patients and week 0 for heathy controls
Comparison of motor performance between patients and healthy controls	The differences in motor performance between FND patients and healthy controls were measured by the accuracy with which they maintained an isometric contraction during index finger abduction at 10% of maximum force.	At TMS session, week 2 for patients and week 0 for heathy controls
Satisfaction rating of patients on the intervention	Patients will be asked to rate their satisfaction after the intervention on a scale from 1 to 10.	At the end of the last intervention session at week 7
Changes in upper limb strength, measured by a grip strength test under different starting conditions, before, during and after taVNS intervention.	Grip strength measured with hand-held dynamometer (Jamar). The different starting condition was pressing freely or pressing after a cue.	weeks 2, 3, 4, 5, 6, 7
Changes in parasympathetic tone measured by heart rate variability	A sport belt would continuously record the heart rate of patients during physiotherapy sessions.	During intervention sessions at weeks 3, 4, 5, 6, 7
Change in functional connectivity, measured by resting-state fMRI	Study the differences in functional connectivity of the brain in patients at the beginning and end of the experimental protocol.	weeks 0, 8
General heath condition questionnaire	Use of the questionnaire SF-36 (Medical Outcomes Study Short Form Health Survey) fill by participants to evaluate their heath condition (score between 0-bad and 100-good).	week 0
Study the evolution of symptom severity score	The patients completed the Subjective Evaluation of Symptom Severity (SSS) questionnaire, which uses a continuous scale ranging from 0 (no symptoms) to 100 (the most severe symptoms experienced) for each session. For the intervention sessions, they fill it twice (before and after the intervention).	weeks 1, 2, 3, 4, 5, 6, 7, 8
Study evolution of perceived stress	The patients completed the Perceived Stress Scale (PSS) questionnaire with 4 items, which uses a score from 4 (no stress) to 20 (extremely stressed). For the intervention sessions, they fill it twice (before and after the intervention).	weeks 1, 2, 3, 4, 5, 6, 7, 8
Study the evolution of the clinical global impression score	The investigator will assess the severity of the patient's symptoms using a scale ranging from 0 (normal, not at all unwell) to 7 (among the most severely unwell) at each session. For the intervention sessions, the evaluation is done twice (before and after the intervention).	weeks 1, 2, 3, 4, 5, 6, 7, 8
Study the evolution of depression evaluation	The patients completed the Beck Depression Inventory (BDI-II) questionnaire before and after the intervention period. The questionnaire uses a score ranging from 0 (not depressed) to 63 (extremely depressed).	weeks 2, 8
Study the evolution of stress evaluation	The patients completed the State-Trait Anxiety Inventory (STAI) questionnaire before and after the intervention period. The questionnaire uses a score ranging from 20 (not stressed) to 80 (extremely stressed) for the state and the trait separetely.	weeks 2, 8
Study the evolution of interoception evaluation	The patients completed the Multidimensional Assessment of Interoceptive Awareness (MAIA) questionnaire before and after the whole protocol. The questionnaire uses a score ranging from 0 (poor interoceptive sensitivity) to 40 (excellent interoceptive sensitivity).	weeks 0, 8
Study the evolution of functional movement disorders rating scale	The investigator performed Simplified Functional Movement Disorders Rating Scale (sFMDRS) questionnaire before and after the intervention period. The questionnaire uses a score ranging from 0 (no symptoms) to 48 (extremely symptomatic).	weeks 0, 8
Satisfaction rating of physiotherapists on the intervention	Physiotherapists will be asked to rate their satisfaction after the intervention on a scale from 1 to 10.	At the end of the last intervention session at week 7

Collaborators and Investigators

• Sponsor: University of Fribourg
• Collaborators: Hôpital Cantonal de Fribourg
• Investigators: Study Director: Cristina Concetti, PhD, University of Fribourg

Study record dates

Study Major Dates

• Study Start (Estimated): July 1, 2026
• Primary Completion (Estimated): July 1, 2028
• Study Completion (Estimated): December 1, 2028

Study Registration Dates

• First Submitted: June 24, 2026
• First Submitted That Met QC Criteria: July 16, 2026
• First Posted (Actual): July 17, 2026

Study Record Updates

• Last Update Posted (Actual): July 17, 2026
• Last Update Submitted That Met QC Criteria: July 16, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: fMRI; TMS; vagus nerve stimulation; motor; VNS; FND; Functional Neurological Disorder
• Additional Relevant MeSH Terms: Mental Disorders; Somatoform Disorders; Conversion Disorder
• Other Study ID Numbers: 2026-D0047

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES

IPD Plan Description

Participants had the option of signing an informed consent form to allow their coded data to be shared with the scientific community.

At the end of the project, the de-identified raw data would be published in a public repository on the Zenodo platform.

• IPD Sharing Time Frame: The public repositories would be made available to the public after the publication date of the relevant scientific article.
• IPD Sharing Supporting Information Type: ANALYTIC_CODE

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No