This study tests if a method called Deep Brain Stimulation (DBS) can help adults with a tough type of depression called Major Depressive Disorder (MDD). DBS is like a tiny "pacemaker" for the brain, sending small signals to a part called the subcallosal cingulate. The study lasts 12 months and is double-blind, meaning neither the participants nor the researchers know who is getting real DBS or a "sham" (fake) treatment. After 12 months, everyone will find out what treatment they received, and those on the "sham" will switch to the real DBS. To join, you must have had depression for at least a year or had it three times in your life and tried at least four different treatments that didn't work. You can't join if you're pregnant, have other brain issues, or if you have problems that might affect the study.

• The study will last for 12 months.
• Participants will not know if they receive real or sham treatment until the study ends.
• Participants must have tried at least 4 antidepressants that didn’t work before.