Laughing gas may reveal brain clues for depression

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Inclusion criteria common to all participants * Female between 25 and 50 years of age * A person who can undergo N2O diffusion via a facial mask. * A person who has signed an informed consent. * Person affiliated with a social security scheme. * Inclusion Criteria for Depressive Patients * Major Depressive Episode according to DSM-5 criteria, confirmed by the MINI - International Neuropsychiatric Interview. * Patients with an MADRS score greater than 20 (Montgomery * Asberg Depression Rating Scale). * Patients resistant to at least one well-conducted antidepressant treatment, as documented by the MGH-ATRQ scale. * Absence of: bipolar disorder, schizophrenic disorder, neurodegenerative disease, schizophrenic disorder, neurodegenerative disease, addiction to one or more toxics documented by the MINI. * Inclusion criteria for healthy voluntary controls * Absence of: bipolar disorder, schizophrenic disorder, neurodegenerative disease, schizophrenic disorder, neurodegenerative disease, addiction to one or more toxics documented by the MINI, current or past. Exclusion Criteria: * Unstable somatic pathology (including unstable neurological or cardiological pathologies at risk of interfering with N2O diffusion) * Presence of active and significant psychotic symptoms, at investigator's discretion * Contraindications to mixture 50%N2O/ 50%O2: intracranial hypertension, altered state of consciousness, head trauma, pneumothorax, emphysema bubbles, abdominal gaseous distension, administration of less than 3 months of ophthalmic gas (SF6, C3F8,C2F6) used in eye surgery, known and unsubstituted deficiency in vitamin B12 or folic acid, recent and unexplained neurological abnormalities. * Contraindications to MRI, including claustrophobia. * Female who is pregnant or breastfeeding or able to procreate without an effective contraceptive method * Legal incapacity and/or other circumstances rendering the patient unable to understand the nature, purpose or consequences of the study (including major under legal protection). * A person participating in a drug clinical trial or during a period of exclusion from any clinical study due to previous involvement.