DBS for TRD With the Medtronic Percept PC

Inclusion Criteria: * Age 25-70 years old. * Ability to provide written informed consent. * Primary psychiatric diagnosis of Major Depressive Disorder (MDD), either single episode or recurrent type, without psychotic features, currently experiencing a Major Depressive Episode (MDE), as diagnosed by Structured Clinical Interview for DSM IV-TR or DSM-5 (SCID-IV or SCID-5). Two independent psychiatrists will confirm the diagnosis, as well. * Current depressive episode of at least two years duration OR a history of more than 3 lifetime depressive episodes. * Minimum score at study entry of 20 on the 17-item Hamilton Depression Rating Scale * Average pre-operative HDRS-17 score of 20 or greater (averaged over four weekly pre-surgical evaluations during the four weeks prior to surgery) * A maximum Global Assessment of Functioning of 50 or less. * Confirmed to have treatment-resistant depression (TRD). Treatment-resistance will be defined as failure to respond to at least four adequate antidepressant treatments (assessed with the Antidepressant Treatment History Form \[ATHF-SF\] and verified through medical records) during the current episode. Treatments which support study inclusion include antidepressive medications, certain augmentation agents, evidenced-based psychotherapy, and neuromodulation (ECT, transcranial magnetic stimulation (TMS)). For those patients who have not received ECT, patients may be considered eligible for study participation if they have received adequate trials of an SSRI, SNRI, augmentation agent (certain atypical antipsychotic medications, Lithium), and TMS and/or ketamine. * ability comply with study and device management procedures. Exclusion criteria: * Other primary Axis I conditions * Active suicidal ideation with intent, suicide attempt within the last six months, more than three suicide attempts within the last two years, or serious suicide risk as determined by the study psychiatrists * Other primary neurological disorders or unstable medical illness * Conditions requiring anticoagulant therapy which cannot be discontinued for the perioperative period, as required * Pregnancy or plan to come pregnant during the study * Contraindications for general anesthesia, neurosurgery, or an MRI scan * Currently implanted with a cardiac pacemaker / defibrillator or other implanted electrical device which may interfere with DBS stimulator or the function of which may be impacted by its implantation.