There are over 100,000 people currently living with DBS brain implants; most are being treated for symptoms of Parkinson’s disease. The device itself is simple, just a pair of wires connected to a battery pack implanted beneath the skin. It’s not a cure, but by sending small electrical shocks to the regions of the brain that govern movement, doctors are able to keep the tremors of Parkinson’s in check. Other movement disorders like Rebecca Serdans’ dystonia respond the same way. With a pair of wires, five years of declining motor control can be reversed.

With a pair of wires, five years of declining motor control can be reversed

Every patient remembers getting the surgery, for the simple reason that they’re awake when it happens. They need to be. The human brain is so varied that the only way surgeons can navigate it is by testing the effects of an electric pulse on different regions. For instance, one center might paralyze the left half of your body, while another produces global aphasia, leaving you unable to form words. The surgeons create a kind of roadmap to the brain that helps guide them to the optimal placement. On one occasion, a doctor at UCLA went so far as to broadcast the procedure in real time on Twitter. The patient even brought a guitar and strummed it as the surgery went along. He wanted to be sure he would still be able to play it on the other side.

The results are as reliable as flipping a light switch, but even after decades of testing, no one knows exactly why it works. Dr. Kaplitt, the surgeon who installed Rebecca Serdans’ implant, explains it by likening the brain to a collection of electrical circuits. A disorder like dystonia is a failure of those circuits. When you install a brain stimulation device, “it's presumably blocking abnormal information from getting from one part of the brain to another, or normalizing that information.” But Kaplitt is the first to acknowledge that this is just a theory. “The mechanism by which brain stimulation works is still somewhat unclear and controversial.”

But the lingering questions haven’t slowed down research. There are already patents that would use brain stimulation implants to enhance memory or prevent stuttering, to cure anorexia or bring a person to orgasm. Experimental studies use the device to treat Alzheimer’s disease and drug addiction. Those circuits aren’t as well understood as the circuits governing movement disorders, but the principle is no different. Once you’ve got a line into the circuitry of the brain, Parkinson’s is just the beginning.

"I really think that brain stimulation in psychiatry is the biggest revolution in the last 50 years."

At the same time, the economic incentives are undeniable. Medtronic, the largest brain stimulation device manufacturer, made $1.7 billion from the implants last year. This has prompted a search for more ways to use the device, including a seizure-sensing model that preemptively responds to epileptic attacks, which is slated to begin human trials this year.

Psychiatrists are also finding uses for the technology. At the University of Bonn in Germany, Dr. Thomas Schlaepfer is using the implant to treat severe depression. Instead of the movement centers, Schlaepfer's treatment targets the brain’s reward centers, taking depression as a malfunction of the neurological reward mechanism. “I really think that brain stimulation in psychiatry is the biggest revolution in the last 50 years,” he says, “because it offers some hope for patients who had little or nothing to hope for.”

Schlaepfer makes a point of saying he’s trying to restore the brain to normal function, but it’s not the only place his research could go. He admits that a less ethical scientist could use the device to create a state of constant reward, something he calls "heroin in electrical form." It wouldn’t be useful in treating depression, but it would be as simple as reprogramming the device, and it would take just half an hour in a doctor’s office.