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

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.

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.