Call them brain pacemakers, tiny implants that hold promise for fighting tough psychiatric diseases - if scientists can figure out just where in all that gray matter to put them.
Deep brain stimulation, or DBS, has proved a powerful way to block the tremors of Parkinson's disease. Blocking mental illness isn't nearly as easy a task.
There is, however, a push to expand research into how well these brain stimulators tackle the most severe cases of depression, obsessive-compulsive disorder and Tourette's syndrome - to know best how to use them before too many doctors and patients clamour to try.
"It's not a light switch," cautions Dr Michael Okun of the University of Florida.
Unlike with tremor patients, the psychiatric patients who respond to DBS tend to improve only gradually, sometimes to their frustration.
Just because the tics of Tourette's fade or depression lightens doesn't mean patients can abandon traditional therapy. They also need help learning to function, much as recipients of hip replacements undergo physical therapy, says Dr Helen Mayberg of Emory University.
"Once your brain is returned to you, you have to learn to use it," she told the annual meeting of the American Association for the Advancement of Science.
Roughly 70,000 people around the world have undergone deep brain stimulation for Parkinson's or other movement disorders when standard medications fail, says Okun, among leading researchers who gathered at that meeting last week to assess the field.
How does it work?
Surgeons implant a wire deep in the brain. Tiny electrical jolts - running from a pacemaker-like generator near the collarbone up the neck to the electrode - disable overactive nerve cells to curb the shaking.
Scientists figured out which spot to target, based on surgery that sometimes helps worst-case Parkinson's patients by destroying patches of brain tissue.
But with deep brain stimulation, the electrodes don't destroy that tissue. The electrical signals can be adjusted or even turned off if they don't help, or if they cause neurological side effects. (The surgery, however, does sometimes cause dangerous brain bleeding or infections.)
Psychiatric illnesses require a similar operation, but surgeons must implant the electrode into a different spot in the brain.
Best spot unknown
It's not clear which spot is best for which psychiatric disease. In fact, two manufacturers, Medtronic and St Jude Medical -have begun major studies of DBS' effects on depression. Each places the implant in a different region, based on promising pilot studies.
The Food and Drug Administration in 2009 approved Medtronic's version for a small group of obsessive-compulsive patients who get no relief from today's treatments, in a special program that allows devices for rare conditions to be sold before final proof that they work.
Dr Joseph Fins, medical ethics chief at New York Presbyterian Hospital, worries that this might hurt efforts to get such proof. The more readily available the electrodes are, the more people may seek to try the $30,000 (about R210,000) surgeries without enrolling in strict trials.
How good is the evidence so far? The researchers are pushing for a registry to track DBS recipients to help the investigation, but overall they're cautiously optimistic.
Just over 60 people with intractable obsessive-compulsive disorder have undergone DBS since 2000, says Dr Benjamin Greenberg. About three-fourths of the first few dozen patients studied improved significantly, some for as long as eight years.
"You still have a burden, but you have a life," is how he describes the improvement.
These are people who try to relieve fears or anxiety with obsessive behaviour, such as washing their hands or checking locks repeatedly, many of whom never got out of the house because their daily rituals consumed so much time, Greenberg says. They'd failed behaviour therapy designed to teach that whatever they fear doesn't happen if they skip the ritual.
But with the brain pacemaker, somehow that behaviour therapy starts working, Greenberg says - maybe by enabling their brains to better remember the lessons.
One big hurdle
The battery, tucked near the collarbone, tends to last less than two years. Changing it entails outpatient surgery, one reason that about a third of studied patients stop getting zapped. So Greenberg recently began testing a newer version that patients can recharge every few days.
Results on about 100 DBS patients with severe depression have been published so far, and roughly half improve regardless of which of the two targeted brain regions is zapped, says Emory's Mayberg, who shares a patent licensed to St Jude.
Separately, she's now studying what the successfully treated brains have in common that might help predict the best candidates, hoping to ease "a tremendous burden on the patients" as they decide whether to try these experiments.
(Sapa, Lauren Neergaard, February 2011)