Non-Surgical Brain Stimulation Shows Promise, but Unknowns Remain

When medication and psychotherapy don't prove effective against depression, some patients find relief from another source: noninvasive brain stimulation.

"Patients are usually treated with medications and treated with psychotherapy, and if that's not enough, then they come to our clinic and consider noninvasive brain stimulation, or specifically TMS," says Dr. Michael D. Fox, an assistant professor of neurology at Harvard Medical School and an associate director of the Berenson-Allen Center for Noninvasive Brain Stimulation at Beth Israel Deaconess Medical Center in Boston. "The main FDA-approved indication for TMS -- transcranial magnetic stimulation -- is depression."

The non-surgical treatment involves holding an electromagnet on the surface of a person's scalp over a region of the brain called the frontal cortex to produce a change in brain activity. For depression, people come in every day, five days a week, for multiple consecutive weeks to receive the treatment, which can lead to a lasting improvement, Fox says. "There's now been multiple large clinical trials showing that TMS does appear to be effective for depression above and beyond just a placebo effect," he says of the treatment that's approved only for people who have failed to respond to medication to treat depression. Up to 20 percent of patients who undergo TMS experience mild headaches that typically go away shortly after treatment; the most severe side effect is seizure, Fox says, though it's rare, occurring in less than 1 in every 1,000 patients.

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Beyond depression, there's been many studies looking at noninvasive brain stimulation as a possible treatment for a range of psychiatric and neurological disorders like Parkinson's disease. For example: "There's some evidence that you can improve Parkinson's symptoms," Fox says, such as reducing stiffness, slowness of movement and difficulties walking, with noninvasive brain stimulation.

But while some research is promising, experts say many unknowns remain both in terms of TMS, and a lower-voltage variety of noninvasive brain stimulation called transcranial direct current stimulation, or tDCS. Not yet FDA-approved to treat any particular condition, tDCS has nonetheless been widely studied for applications ranging from treatment of depression and anxiety to neurological disorders; it has also been explored as a means of boosting a healthy person's cognitive abilities, such as problem-solving or learning potential.

The buzz over noninvasive brain stimulation has even spawned a niche consumer market, with gadgets available for purchase online that aim to deliver the type of low levels of electrical stimulation administered in tDCS research. That's raising concerns about potential safety hazards. At present, it's not not clear whether the devices will be regulated by the Food and Drug Administration as medical devices.

More sophisticated models connect to iPhones, while simpler devices essentially consist of two wires with electrodes attached to a 9-volt battery, and cost as little as $50, says Anna Wexler, a graduate student at MIT in Cambridge, Massachusetts, who is doing her Ph.D. research on the consumer use of noninvasive brain stimulation. Some DIYers build the devices from scratch. Typical brain stimulation do-it-yourselfers or home users are male, in their 20s to 50s, well-educated and employed, who are using it in an attempt to achieve cognitive enhancement or treat depression as well as other issues like anxiety, according to Wexler; some professionals and students use the gadgets in hopes of gaining a mental edge. "They want to improve their working memory. Maybe they want to increase their learning ability. [Or] they're taking a class and they want to be able to study better," she says. So they turn to home brain stimulation, despite the unproven nature of the gadgets and the many unknowns still surrounding the technology.

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While Wexler describes it as a subculture, the emergence of home use has garnered the attention of not only regulators but researchers, and it's providing a glimpse into both the promise and unknowns of noninvasive brain stimulation, in particular tDCS.

Recently, several brain stimulation experts penned an open letter concerning do-it-yourself tDCS, which was also signed by 39 other experts in the field, detailing the potential pitfalls associated with the technique. The letter, for which Fox was a corresponding author, was published in July in the Annals of Neurology, a journal of the American Neurological Association and the Child Neurology Society.

"Whereas some risks, such as burns to the skin and complications resulting from electrical equipment failures, are well recognized, other problematic issues may not be readily apparent," the authors wrote. "We perceive an ethical obligation to draw attention to both professionals and DIY users to some of these issues." Stimulation, for example, may affect more areas of the brain than a user might expect. What's more, not everyone will respond the same way to the same pulses of energy. There may also be "trade-offs" to any gains reaped: While tDCS may increase the rate a person learns new material, for example, it could negatively affect one's ability to process what they learn. In short, experts say, it's unclear all the ways the technology could affect the brain.

"To our knowledge, tDCS is pretty safe technology. It has not yet been associated with serious adverse effects," says letter co-author Dr. Roy Hamilton, an assistant professor of neurology and director of the Laboratory for Cognition and Neural Stimulation at the University of Pennsylvania in Philadelphia. Nor does he suspect it will be, based on research to date. But given the experimental nature of the technology and the profound complexity of the brain, experts say there's still much to learn.

The same caution extends to using the technology to improve cognition or to treat a disorder like depression. "I would definitely recommend that people contact a health provider before they use tDCS to try and treat a specific neurological or psychiatric disease," Fox says.

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For healthy individuals considering using noninvasive brain stimulation to attempt cognitive enhancement, the risk-benefit ratio is very different, clinicians and researchers say, than for patients undergoing experimental tDCS treatment for brain disease. "In other words, if your brain is already not working correctly, we'll accept a little bit more risk and a little bit more unknowns in order to try and get patients better," Fox says. "But when your brain is already working well, those unknowns and that level of risk become a little bit more concerning."

Michael Schroeder is a health editor at U.S. News. You can follow him on Twitter or email him at mschroeder@usnews.com.