This study aims to compare the efficacy and safety profile of Magnetic Seizure Therapy and Electroconvulsive therapy.

Magnetic seizure therapy (MST) is a novel, experimental therapeutic intervention, which combines therapeutic aspects of electroconvulsive therapy (ECT) and transcranial magnetic stimulation, in order to achieve the efficacy of the former with the safety of the latter. While ECT remains the most efficacious treatment available for severe and treatment-resistant depression, it is hampered by its side effect profile, specially cognitive deficits, which albeit transitory might be particularly distressing for patient, not to mention the stigma that still clings to this method. MST employs high frequency magnetic pulses applied to the head to the patient in order to induce generalized epileptic activity, thus emulating the core feature of ECT. Though distributed over a large area, such pulses do not penetrate deeper areas of the brain, therefore sparing deeper areas such as the hippocampi, which are crucial for memory encoding.

The goal of this study is to compare the antidepressant action and safety profile of MST to ECT, using a non-inferiority approach. It also aims to compare the cognitive side effects profile of both interventions, as well as investigate possible neuroimaging changes and response predictors before and after treatments.

Inclusion Criteria:

• Major Depressive Disorder or Bipolar Depression in accordance to the Diagnostic and Statistical Manual (DSM) criteria
• Score equal to or great than 17 points on the Hamilton Depression Rating Scale
• Treatment-resistant depression, defined as insufficient relief of symptoms after two different first line treatments using therapeutic doses and for four to six weeks
• Adequate health and clinical conditions, as assessed by an anaesthesiologist and a psychiatrist

Exclusion Criteria:

• Pregnancy
• Other psychiatric conditions such as Schizophrenia, Schizoaffective Disorder, Substance Abuse, Borderline Personality Disorder, PTSD, or Intellectual Deficiency
• Depressive symptoms due to a clinical condition
• Any clinical or neurological conditions without proper management
• ECT or any other neuromodulation treatment on the last six months
• Inability to consent

Patients will be anaesthetised before the procedure, therefore will not be able to tell whether they received ECT ou MST. The preparation procedures before seizure will be identical for all participants regardless of the intervention. All monitoring and other procedures will be exactly the same for both groups. Investigator and rater will not have access to which procedure subjects received. To blind the staff, the MST sound will performed during all study interventions.