The small, 20-patient trial, published in the journal Biological Psychiatry, also found 35 per cent of patients were still largely free of symptoms 12 months after surgery.
"There were striking improvements in patients who were resistant to all other forms of treatment," said Dr. Andres Lozano, the study's principal investigator and neurosurgeon at the Krembil Neuroscience Centre at Toronto Western Hospital. Patients who participated in the study were considered untreatable because drugs, psychotherapy and electroshock therapy had not relieved symptoms.
Lozano, who helped pioneer the use of deep brain stimulation, or DBS, to treat depression, said the study provides further evidence the technique could be a valuable therapy for patients who have run out of treatment options.
Some 120 million people worldwide suffer from depression, and current treatments help 80 per cent of patients, said Lozano.
DBS, which relies on technology similar to a cardiac pacemaker, has had success in relieving the tremors of Parkinson's disease.
Previous research pointed Lozano and his colleagues to a region of the brain that appeared dysfunctional in patients with depression.
"The activity in this area is hyperactive, or overactive, in patients with severe depression. By placing electrodes in the region and continuously stimulating it with electricity 24 hours a day, we could turn down the activity in this area."
DBS did not cause any cognitive damage, which Lozano said is another potential benefit of the therapy. Electroshock therapy, which is used to treat depression in 100,000 people every year, is associated with adverse effects, he said.
The next step is to investigate DBS in a large population of patients. A 200-patient trial involving 15 centres in Canada and the U.S. is under way with results due in three years.