Under the skin, a battery is surgically implanted -- generally within the upper chest. From the battery, wires snake up to the head, to tickle different targets deep inside the brain.
Such is the hardware for deep brain stimulation -- the equivalent of a cardiac pacemaker for the mind.
Until recently, deep brain stimulation was approved in the U.S. only to treat certain movement disorders, primarily those of Parkinson's disease, for which it diminishes tremors and rigidity and improves mobility. To date, more than 60,000 patients worldwide have had the devices implanted.
But now use of the technique seems set to mushroom.
This year, the Food and Drug Administration granted a so-called humanitarian device exemption for the treatment to be used in severe cases of obsessive-compulsive disorder -- the first approval of deep brain stimulation therapy for any psychiatric condition.
Large clinical trials are also in the works for use of deep brain stimulation for epilepsy and depression, and experimental studies in the U.S. and elsewhere -- still in their early stages -- are exploring the treatment for obesity, traumatic brain injury, severe chronic pain, Alzheimer's disease, anorexia, tinnitus and addiction.
There are discussions too on the possible use of deep brain stimulation to treat hypertension.
"The field is taking off," says Dr. Ali Rezai, director of functional neurosurgery at the Cleveland Clinic, who has been involved in research on movement disorders, traumatic brain injury, obsessive-compulsive disorder and severe depression, among others.
Some researchers warn, however, that with all this activity -- pushed in part by the industry that makes the brain-stimulation devices -- the field may be moving too fast.
"There is so much progress that's been made and so much potential -- you would hate to lose that potential," says Dr. Joseph Fins, chief of the division of medical ethics and a professor at Weill Cornell Medical College in New York.
Here's a look at deep brain stimulation as it moves beyond Parkinson's disease. (See the related story about reservations scientists have about the growth of the field, and go online at latimes.com/health for a look at less-explored applications such as traumatic brain injury and obesity.)
In studies with a total of 26 patients with severe obsessive-compulsive disorder, 60% of those whose device was turned on demonstrated "very much improved" symptoms after months of deep brain stimulation as measured by interviews and questionnaires, says Dr. Benjamin Greenberg, an associate professor at Brown University Medical School and Butler Hospital in Providence, R.I., who was one of the study researchers.
The patients had previously failed on medicines as well as behavioral cognitive therapy.
Yet the data, published last year in Molecular Psychiatry, can't really nail the effect of the treatment, Greenberg says, because the patients for the most part knew whether their devices were turned on or off. Thus, researchers can't rule out that some of the observed improvements were due to a placebo effect.
Patients were stimulated in an area called ventral capsule/ventral striatum, chosen, in part, because removal of nerve fibers in that area is known to cause improvement in obsessive-compulsive symptoms.
Based largely on these findings, the FDA recently granted a limited humanitarian device exemption that permits the device to be used in as many as 4,000 of the country's most severe cases of obsessive compulsive disorder per year.
To get this kind of exemption, Medtronic -- makers of the only deep brain stimulation device that is FDA-approved -- needed only to show its safety and probable benefit.
Greenberg is now doing a randomized, double-blinded trial with 30 patients, some of whom have devices turned on right away and some who have them turned on after a delay. No one will know whose device is turned on for the first several months of the trial.
Medtronic has conducted a large-scale randomized trial for deep brain stimulation on epilepsy. Data will be submitted to the FDA this year, says Paul Stypulkowski, senior director of therapy research of Medtronic.
The device was turned on, for three months, in half of the 110 volunteers, stimulating -- and thereby, paradoxically, inhibiting -- an area called the anterior nucleus of the thalamus. That area is believed to influence a circuit involved in seizures.
The data, presented in December at a meeting in Seattle, show that deep brain stimulation reduced the number of seizures by 38% compared with what was seen before implanting the device.
That is slightly better than improvement seen with vagus nerve stimulation, another FDA-approved electrical stimulation treatment, which reduces seizures by about 25%.