WASHINGTON — It’s a new frontier for psychiatric illness: Brain pacemakers that promise to act as antidepressants by changing how patients’ nerve circuitry fires.

Scientists already know the power of these devices to block the tremors of Parkinson’s disease and related illnesses; more than 40,000 such patients worldwide have the implants.

But psychiatric illnesses are much more complex and the new experiments with so-called deep brain stimulation, or DBS, are in their infancy. Only a few dozen patients with severe depression or obsessive-compulsive disorder so far have been treated in closely monitored studies.

Still, the early results are promising. Dramatic video shows one patient visibly brightening as doctors turn on her brain pacemaker and she says in surprise: “I’m starting to smile.” And new reports this month show that some worst-case patients — whose depression wasn’t relieved by medication, psychotherapy, even controversial shock treatment — are finding lasting relief.

Six of 17 severely depressed patients were in remission a year after undergoing DBS and four more markedly improved, and more than half of 26 obsessive-compulsive patients showed substantial improvement over three years, according to studies from a team at the Cleveland Clinic, Brown University, and Belgium’s University of Leuven.

“Not all patients get better, but when patients respond, it’s significant,” Dr. Helen Mayberg of Emory University, who has implanted about 50 depression patients, said.