CLEVELAND -- Researchers are reviewing a unique brain surgery to treat the most severe cases of clinical depression.

The Cleveland Clinic and Brown University researchers are studying candidates to determine whether a brain surgery that helps stop tremors in Parkinson's disease patients can also help treat major depression. It's a surgery with potentially serious risks.

"It's a very precise surgery, you have to be precise to 1 mm, otherwise you may be in the wrong place," said Cleveland Clinic researcher Dr. Ali Rezai.

The surgery is called deep brain stimulation, which it uses high-resolution imaging. Surgeons place tiny electrical devices in the area of the brain that controls mood. They then implant pacemakers in the chest and connect it to the electrical devices. The signals help fine-tune abnormal brain activity.

"What this surgery does it improves their mood so patients can go about living their life more fuller and not be so disabled by their condition," Rezai said.

Preliminary study results show that one year after surgery, two-thirds of the participants had a "significant reduction" in the severity of their depression.

Researchers are also studying the effects of deep brain stimulation on people who suffer from obsessive compulsive disorder, a brain disorder in which people have little or no control over repetitive behaviors like washing their hands. Preliminary results found that after two years, patients showed significant improvement with symptoms of OCD.

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