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Imagine a device that in just 30 minutes makes your brain more receptive to new information, cutting the time it takes to learn in half. Some neuroscientists say they have demonstrated this very feat.

Their work is part of an effort to explore how low levels of continuous electrical current, delivered to the brain via electrodes placed on the scalp, could alter neural activity and improve a person’s performance.  In one experiment, for example, electric stimulation accelerated how quickly participants learned to spot concealed bombs or snipers in a military training simulation.

“We almost doubled people’s learning rate,” says Vincent Clark, a professor of psychology and clinical neuroscience at the University of New Mexico who conducted this research with his colleagues. Since the 2012 publication of that research, he and other scholars have replicated the study several times with similar results.

Clark’s study is not a lone example. Findings suggest this form of electric stimulation — known as transcranial direct current stimulation, or tDCS — could make you better at math, more creative and even boost memory. Last year, the federal Defense Advanced Research Projects Agency (DARPA) announced it would support a program using this technique in order to explore whether tDCS could accelerate foreign language learning by 30 percent. (The Department of Defense also financed the University of New Mexico team’s research.) And some members of the U.S. ski jumping team competing in the Winter Olympics trained using electric stimulation headbands from the company Halo Neuroscience, which sells their headsets to the general public.

The technique, which has existed for nearly two decades, is relatively simple. People place electrodes over regions of the brain relevant to a given task, then activate the electric stimulation while practicing that task. Researchers believe the electricity can encourage brain cells to form new connections and that such connectivity is fundamental to the process of learning. Transcranial direct current stimulation is one of several non-invasive approaches used to stimulate the brain, but it’s unique in that brave do-it-yourself-ers are trying out tDCS at home. That’s because the equipment is fairly cheap and safety concerns are minimal. At its most basic, the electrodes and a nine-volt battery can cost less than $100. Several studies have found only minor side effects: at worst, skin discomfort under the electrodes.

There’s evidence its popularity is steadily growing. For several years, Reddit has hosted a forum on DIY tDCS; it attracts as many as 10,000 visitors each month who trade opinions on topics such as which headset to purchase or how to use stimulation to help with mastering the guitar. On Youtube, enthusiasts share how they experienced “euphoria” during stimulation or improved their chess performance.

But more recently, companies have made it easier for people to try tDCS at home. On Amazon, the Halo headset, which costs $719, features more than 100 reviews and a four-star rating. Caputron, which sells tDCS equipment, has noted a surge in sales around exam time, leading the company to suspect that college students are zapping their brain to boost study sessions. (In light of that pattern, CEO Robin Azzam notes that the company now sends out discount codes during those timeframes.)

Related: How to study smarter

But for all of the excitement about this approach to mind enhancement, there’s a lot that’s still unknown. And that’s especially true for students who are seeking an edge during cram time.

“The evidence base, as far as the ability to make you perform well on exams and other things, is absolutely incomplete, which is not to say it does or does not work,” says Marom Bikson, a professor at the Grove School of Engineering at the City College of New York, who has studied tDCS.

Bikson says the research on how tDCS might affect attention, behavior and cognition is still young. He also suspects that, as when students take Adderall or down coffee during exam time, those using tDCS “off-label” are influenced more by anecdotes about the experience than by hard data.

And there are plenty of reasons to be wary of the claims surrounding electric stimulation, according to Emiliano Santarnecchi, a Harvard Medical School instructor in neurology. He says, “It’s not as simple as it seems.”

Santarnecchi employs electrical stimulation in his research and sees it as a powerful tool for learning about the brain. But he says the strongest evidence of tDCS’s effectiveness as a cognitive enhancer comes from studies that pool data from multiple published papers, looking for an overall effect. Unfortunately, that strategy often involves combining many small studies of poor quality to yield a seemingly more significant result. It also means unpublished data that did not find an effect associated with stimulation are neglected.

Santarnecchi says he is also concerned by the lack of knowledge surrounding the effects on other brain regions as a particular area is stimulated. It’s possible, for example, that there might be a hidden cost, such as damage to an unstimulated part of the brain. Nor do we know much about the long-term effects of repeated use of tDCS or if the brain habituates to stimulation over time.

He also emphasizes that every brain is different and it’s hard to know how any one person might react to tDCS. Some data suggest that people may respond differently based on their genes or even their skill in the domain they’re trying to improve. For example, in 2016, one research team found that stimulating part of the prefrontal cortex — an area of the brain that’s involved in thinking and decision making — could improve improvisational ability in amateur jazz musicians but might harm the performance of experts.

And there are those who doubt the efficacy of tDCS altogether. Some scientists argue that many of the gains people attribute to brain zapping could be chalked up to a placebo effect. (A tingling sensation at the scalp, after all, would surely cause many of us to believe something interesting is happening.) There are even researchers who challenge whether the electrical current used in these studies can reach the brain at all.

None of these caveats diminish how exciting brain stimulation could be as a possible tool for studying the brain and even a new form of medicine. Stimulating the motor cortex, for example, could help stroke patients make greater gains during physical therapy. Already, tDCS is approved in Europe to help people suffering from pain conditions and depression, and scientists are exploring its potential to help people with epilepsy, schizophrenia and other conditions. (In fact, many DIY-ers are trying to self-treat their depressive symptoms.)

But until more is known about how it works and the best ways to use it, at-home tDCS is very much an “at your own risk” experiment. For some people, that uncertainty is part of the appeal. For the rest of us, it’s worth remembering that we already have some low-risk “biohacks” for learning: eating healthy, staying hydrated, exercising regularly and getting a good night’s sleep.

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