Crucially, the electrode fires only when needed, hundreds of times a day, whenever a specific pattern of brain activity is detected. A simpler form of brain stimulation, in which the device is always on, is already used in the movement disorder Parkinson's disease, where the brain areas involved are relatively well understood. Such continuous brain stimulation has been tried before in depression, but the results from trials have been mixed, perhaps because the brain circuitry responsible is unclear. When trying to help Sarah, Scangos's team started by recording the electrical activity from 10 different parts of her brain while she reported on her mood, over 10 days. Sarah had experienced depression since childhood that couldn't be helped by many different drug treatments and electroconvulsive therapy. Before the surgery, she was experiencing suicidal thoughts several times an hour.