Inclusion Criteria:  Primary DSM-5 diagnosis of Major Depression as assessed by the M.I.N.I with a single or recurrent episode with the additional requirements of a current episode with a duration of ≥4 weeks. Current depressive episode is less than 5 years duration (the definition of an episode is demarcated by a period of ≥2 months in which the patient did not meet full criteria for the DSM-5 definition of major depressive episode). Total HDRS-21 ≥13 at the screening visit. Patient is taking one of the following antidepressants of adequate dose and ≥2 weeks in the current Episode: SSRIs: Escitalopram, Citalopram, Sertralin, Paroxetin, Fluoxetin, Fluvoxamin; SSNRIs: Duloxetin, Venlafaxin, Milnacipran. and optional concomitant treatment with Quetiapin, Lithium und Mirtazapin. Capable and willing to provide informed consent. Negative pregnancy test and willingness to use contraceptive measures during study treatment for women with childbearing potential (i.e <. 2 years post-menopausal)  Exclusion Criteria:  Investigators, site personnel directly affiliated with this study, and their immediate families Acute risk for suicide (MADRS, item 10 score of ≥4 or suicidal attempt in the present episode Treatment with electroconvulsive therapy in the present episode. Treatment with deep brain stimulation or vagus nerve stimulation and/or any other intracranial implants (clips, cochlear implants). Any other relevant psychiatric axis-I- and/or axis-II-disorder. Any relevant instable medical condition.  Individuals diagnosed with a significant neurological disorder or insult including, but not limited to:  Increased intracranial pressure Space occupying brain lesion History of cerebrovascular accident Transient ischemic attack within two years Cerebral aneurysm, dementia Parkinson's disease Huntington's chorea Multiple sclerosis Epilepsy History of seizures Pregnancy.