For more than a decade, doctors have been using brain-stimulating implants to treat severe depression in people who do not benefit from medication, talk therapy or electroshock sessions. The treatment is controversial — any psychosurgery is, given its checkered history — and the results have been mixed. Two major trials testing stimulating implant for depression were halted because of disappointing results, and the approach is not approved by federal health regulators.Now, a team of psychiatric researchers has published the first long-term results, reporting Friday on patients who had stimulating electrodes implanted as long ago as eight years. The individuals have generally fared well, maintaining their initial improvements. The study, appearing in the American Journal of Psychiatry, was small, with just 28 subjects. Even still, experts said the findings were likely to extend interest in a field that has struggled....The implant treatment is known as deep brain stimulation, or D.B.S., and doctors have performed it for decades to help people control the tremors of Parkinson’s disease. In treating depression, surgeons thread an electrode into an area of the brain that sits beneath the crown of the head and is known to be especially active in people with severe depression. Running electrical current into that region, known as Brodmann Area 25, effectively shuts down its activity, resulting in relief of depression symptoms in many patients. The electrode is connected to a battery that is embedded in the chest. The procedure involves a single surgery; the implant provides continuous current from then on.