WASHINGTON (AFP) – The use of brain surgery to treat psychiatric disorders has long been controversial, but new technologies are emerging that can help people with severe illnesses, scientists said on Friday.

However, experts urged caution because they still do not understand exactly how these therapies work, and so they should be limited to patients with debilitating disorders that cannot be helped by psychotherapy or medication.

One new therapy discussed Friday at the annual meeting of the American Association for the Advancement of Science was the use of deep brain stimulation to ease obsessive compulsive disorder, or OCD.

The technique, approved in 2009 by the US Food and Drug Administration for extreme cases under its humanitarian device exemption, involves the insertion of a thin electrode deep in the brain.

The electrical current has been shown to reduce OCD symptoms by about 25 percent in some patients. The technique has been tried on just over 50 people in the United States since the research first began in 2000.

"These techniques are promising but must be used with an abundance of caution," said Benjamin Greenberg, associate professor of psychiatry and human behavior at the Warren Alpert Medical School of Brown University.

"This is reserved for the small proportion of people who are severely disabled and have not benefitted anywhere near adequately from very aggressive use of conventional treatments."

About one percent of adults are affected by OCD, experts say. To qualify for treatment with the brain electrodes, patients must show "severe and chronically disabling illness despite at least five years of aggressive treatment," Greenberg said.