Male or female patient between 18 and 65 years of age
Sufficient knowledge of the French language to complete the assessments
Inpatients or outpatients with a major depressive episode (DSM-5 criteria);
Score above 19 on the MADRS depression scale (moderate to severe depression);
Without antidepressants, mood stabilizers or antipsychotics treatment or having stopped the previous medication(s) for more than 5 times the half-life of the prescribed treatment(s);
Eligible for antidepressant monotherapy with SERTRALINE or FLUOXETINE or DULOXETINE or MAPROTILINE, with or without benzodiazepine therapy, and in whom treatment is feasible within days of inclusion.
You may not be if
• Patient with bipolar disorder, schizophrenia or psychotic disorder as defined by the DSM-5 and assessed by the MINI or any other pathology or treatment deemed clinically incompatible with the study by the investigator;
* Patient with moderate to severe substance use disorders (\>=4/11 criteria as defined in the DSM-5) and with the exception of smoking disorders
* Patient with pregnancy, unstable physiological condition or severe and symptomatic medical condition;
* Patient with a diagnosed neurological disorder affecting central nervous system function;
* Patient unable to give informed consent to participate in this study or unable to give the volunteer informed information;
* Patient who are not covered by a social security system;
* Patient under court protection or guardianship
* Patient who have received a vaccination within one month prior to initiation of treatment or who plan to be vaccinated within 2 weeks of initiation of treatment \> For patient undergoing MRI: presence of a contraindication for MRI examination.
