Deep brain stimulation (DBS), where electrodes are used to deliver mild electric currents to targeted regions of the brain, is showing promise as a treatment for a range of conditions, including Alzheimer's, Parkinson's and depression. A new study exploring the lattermost of these has returned "absolutely sensational" results, with the reduction of depressive symptoms being not only fast-acting, but in some cases long-lasting.

The study took place over a 12-month period and was carried out by researchers at Germany's University of Freiburg and University Hospital Bonn. In it, 16 subjects suffering from treatment-resistant depression received implantations of thin electrodes in order to stimulate the brain's medial forebrain bundle, widely accepted as a key component in the brain's reward system and therefore linked to pleasure, motivation and quality of life.

All subjects recruited for the study suffered from severe depression and had undergone various drug therapies, psychotherapy, and electroconvulsive therapies, but to no avail. But the DBS treatment brought about almost immediate results, with the researchers measuring their subjects' responses through what is known as the Montgomery-Asberg Depression Rating Scale, a questionnaire used by psychiatrists to measure the severity of a patient's depression.

All of the subjects saw a reduction in depression ratings in response to the treatment, with 10 of the 16 subjects exhibiting significantly lower scores within the first week. Eight of the 16 subjects scored below 10 points at the study's end, which is considered the threshold for depression requiring some form of treatment.

"Our patients had struggled with severe depression for years with no signs of improvement," says Dr. Thomas Schläpfer, head of the Division of Interventional Biological Psychiatry at the University of Freiburg. "Deep brain stimulation brought most of them significant relief within days, which lasted throughout the course of the therapy. Other forms of treatment like medication and psychotherapy often lose their effectiveness over the course of time. What is absolutely sensational about the study data is that the effect seems to be long lasting, with the positive effects continuing for years."

Beyond the wonderful results for the participants of this particular study, the research has uncovered yet another target in the brain for scientists looking to curb treatment-resistant depression. Recent research into DBS treatments for the disorder has brought some promising results, with one study probing the orbitofrontal cortex bringing about significant mood improvements. The scientists involved call this latest research the world's largest study of deep brain stimulation in the brain's reward system, and believe they have uncovered yet another avenue of attack.

"We demonstrated for the first time in a relatively large-scale study that deep brain stimulation is a real option for those patients suffering from treatment-resistant, severe depression," says Schläpfer.

They are now working on a follow-up study in the hope that if these promising results can be replicated, regulatory approval for the therapy will follow.

The research has been published in the journal Neuropsychopharmacology.