Clinical Evaluation of HRV Biofeedback in Functional Neurological Disorders Compared to Placebo

Inclusion Criteria: * Functional Neurological Disorders (FND) diagnosis must be medically established * Participants must have a smartphone (android ou Iphone) * Participants must be of the age of majority * Participants must have signed an informed consent * Sufficiently fluent in French to understand study documents and instructions * Consistency in performing repeated questionnaires * Normal or corrected-to-normal visual acuity Exclusion Criteria: * Specially protected participants: juveniles, pregnant womens, nursing mothers, law's protection peoples * Participants suffering from a severe psychiatric disease needing specialised attention * History of severe neurosurgical pathology * Alcohol dependence or drug use * Participants suffering from or have suffered from a severe disease causing autonomic dysfunctions (heart failure, asthma, blood disease, renal failure, peripheral neuropathy, vagotomy, thyroid disorder, alcoholism, liver disease, amyloidosis) * Participants taking medication which could be impact autonomic nervous system activity (anticholinergic, antiarrhythmics, clonidine, beta-blockers, tricyclic anti-depressants, metronidazole) * Participants placing under judicial or administrative supervisions