I recently had a hormonal implant dug out of my arm because it had 'migrated'. It took three surgeries to get it out. The doctor who performed the second surgery sliced into a vein, mangled the implant still left in my arm and I developed a solid blood clot the size of a golfball. The clot and mangled implant remained in my arm for three more months until I could get a highly competent plastic surgeon to clean up the whole sorry mess, at considerable expense.

If a simple hormonal implant that is meant to be placed sub-cutaneously can cause that much trouble, no-one is going to sell me a DBS, ever. It's about as sophisticated a piece of medical treatment as a lobotomy or stone age trepination. Sometimes they work too, but at what price?