Testing on severely depressed patients shows that electrical brain implants can successfully "reset" the brain's mood switch from sad to normal, with results that last for at least a year, Canadian researchers are reporting.

Deep brain stimulation not only provided "striking" improvements in more than half of patients treated, it also improved mood, anxiety, sleep, appetite control and the ability to put thoughts into action, the team reports in Biological Psychiatry.

Some patients are doing well five years after having electrodes implanted for the deep brain stimulation.

"It's like the butterfly flapping its wings," Toronto neurosurgeon Andres Lozano said. "We're seeing changes locally where we're stimulating, and also in the circuitry of the brain.

"And it's not just a temporary response lasting a week or two."

Improvements were seen within a month, "and remained statistically significant for the entire 12 months of the trial," according to the researchers.

"It appears to be sustained," Lozano reported.

Severe depression affects an an estimated 120 million people worldwide. Deep brain stimulation is geared to the 10 to 20 per cent who are "treatment-resistant," meaning antidepressants, psychotherapy and electroconvulsive therapy, or "shock therapy," don't work for them. Their cases are the "worst of the worst," and about 15 per cent commit suicide, Lozano said.

"There's nothing out there that really makes them better."

Three years ago, his team reported on the first six cases of using deep brain stimulation in major depression. Today, they're reporting on the results of those six patients, plus an additional 14, for a total of 20 followed for at least one year. Nine men and 11 women were treated, the youngest in their 20s, the oldest in their 70s.

"We can confirm, at one year, about 60 per cent of the patients have a significant response," said Lozano, a neurosurgeon at Krembil Neurosciences Centre at Toronto Western Hospital and Canada Research Chair in neuroscience.

The procedure, which is reversible, also appears safe. "We've not seen any serious adverse effects and we've seen, in fact, improvements in some cognitive functions in these patients."

"It really opens up the possibility this could be offered to a much larger number of patients."

About 40,000 patients worldwide have undergone deep brain stimulation to treat Parkinson's disease by stimulating motor circuits in the brain. The Canadians are testing it on depression by targeting circuits that control mood.

The skin of the scalp is frozen and holes the size of a nickel drilled into the skull. Electrodes about the width of spaghetti are implanted in the brain and hooked to a pacemaker, a programmable "pulse generator" implanted under the skin, usually below the collarbone. The device can be controlled through the skin remotely, like you would change the channels on a television.

The surgery targets a region of the brain known as Area 25, where neurons regulating mood are hyperactive. It's as if the thermostat of the mood is set to sad, permanently, Lozano said.

By placing electrodes in this "hot spot" of the brain, they were able to turn down the dial, and return the activity to normal.

Some of the changes were instantaneous: Three-quarters of the patients reported experiencing an immediate effect in the operating room as soon as the current was switched on.

Debra Prupas has tried different drugs in different combinations in her lifelong struggle with depression. She had shock treatments and magnetic therapy. Most of what she tried didn't work. She underwent deep brain stimulation as part of this trial two years ago.

"I had two young children and I was at the point I just couldn't go on," the Toronto lawyer said. "I not only couldn't hide it anymore and just go on with life as usual, I couldn't even get out of bed to take a shower."

There's been steady improvement since the electrodes were implanted. She still struggles sometimes. But she's back at work full-time. She used to feel disconnected from her children, and almost everyone else.

"When the depression started to lift, that joy came back with my children. That was the biggest gift."