Do gadgets like the brain-zapping headphones developed by Halo Neuroscience—and worn by James McAdoo and other players on the Golden State Warriors—really work? Photograph Courtesy Halo Neuroscience

Back in March, James Michael McAdoo, the power forward for the Golden State Warriors, tweeted out a photo of himself in the training room, sporting a pair of slick over-the-ear headphones. Though you couldn’t tell from the picture, these particular headphones incorporated a miniature fakir’s bed of soft plastic spikes above each ear, pressing gently into the skull and delivering pulses of electric current to the brain. Made by a Silicon Valley startup called Halo Neuroscience, the headphones promise to “accelerate gains in strength, explosiveness, and dexterity” through a proprietary technique called neuropriming. “Thanks to @HaloNeuro for letting me and my teammates try these out!” McAdoo tweeted. “Looking forward to seeing the results!”

On Thursday night, McAdoo and his teammates will seek the eighty-ninth and final win of their record-breaking season, as they defend their National Basketball Association title in Game 6 of the final series against LeBron James’s Cleveland Cavaliers. The headphones’ apparent results, in other words, have been impressive. Although a Halo spokesperson declined my request for comment, a Warriors trainer confirmed that an unspecified number of players have been trying the device. This fits in with the team’s techno-utopian narrative. Since the bumbling Warriors franchise was purchased by a group of Silicon Valley venture capitalists, in 2010, it has acquired a reputation as “tech’s team,” playing with the wonky, numbers-driven approach of Sand Hill Road. The Warriors have also been enthusiastic early adopters of technology ranging from “intelligent sleep masks” for countering jet lag to body-worn sensors that detect pressure on the knees and ankles. Given the Warriors’ unprecedented dominance, this is an approach that other teams are likely to emulate. So it’s worth asking: do the brain-zapping headphones and other assorted gadgets really work?

Halo was founded in 2013 by Daniel Chao and Brett Wingeier, who had previously worked together at a company using brain stimulation to treat epilepsy. Halo’s headphones employ a technique called transcranial direct-current stimulation, or tDCS, which, in its simplest form, involves attaching a couple of electrodes to a battery, sticking them to your head, and sending a trickle of mild current—five hundred to a thousand times smaller than that used in electroshock therapy, typically—through your brain. The current changes the excitability of individual neurons, making them slightly more or less likely to fire—neuropriming them, to use Halo’s jargon. The electrodes incorporated in the Halo headphones are positioned to send a current through the motor cortex, where commands to the muscles originate. Don the headphones for twenty minutes during your warmup, activate them with the associated app, and your brain will be ready to deliver “stronger, more synchronous” signals to your muscles, the company claims.

There’s no question that tDCS can have real effects. In the past five years, researchers have published more than two thousand studies exploring the technique’s potential for goals as varied as enhancing learning, fighting addiction and depression, and improving walking ability in patients with Parkinson’s disease. One case study, published in the journal Neuroscience Letters in 2014, describes significant improvements in “trunk peak velocity” during tango dancing in a seventy-nine-year-old Argentinian man with moderate Parkinson’s—a finding that, with a little imagination, might evoke the Warriors swingman Andre Iguodala’s smotheringly intimate pas de deux with James in the defensive end. There’s also no question that tDCS hype has long since diverged from what researchers (or the vibrant D.I.Y. tDCS community) have actually demonstrated, triggering a skeptical backlash. At a conference in April, György Buzsáki, of New York University, presented results from a cadaver study showing that only about ten per cent of the electric current that is applied to a skull even makes it into the brain, prompting one tDCS researcher to describe the field as “a sea of bullshit and bad science.”

The idea that tDCS might help athletes has been around since at least 2007, when Italian researchers showed that stimulating the motor cortex reduced neuromuscular fatigue and increased endurance in the left elbow flexors of a group of volunteers. A subsequent Brazilian study, stimulating areas of the brain associated with effort and self-monitoring, boosted endurance performance in cycling. Not all the results have been positive, though: at the annual meeting of the American College of Sports Medicine in Boston earlier this month, for example, another Brazilian group presented data showing that tDCS failed to improve performance in an intermittent sprint test—the type of challenge that simulates the demands of court sports like basketball.

Weighing the allure of instant brain-boosting against the uncertainty of conflicting data and negative studies, the sports world responded with the wide-eyed optimism of Lloyd Christmas, half of the half-witted duo in “Dumb and Dumber”: “So you’re telling me there’s a chance.” Red Bull was the first to dive in, in 2014, bringing in a team of researchers from Weill Cornell Medical College, in New York, to run a five-day testing session at its Santa Monica headquarters with some of its élite cyclists and triathletes. Halo’s headphones were the inevitable next step—and Andy Walshe, Red Bull’s director of high performance, is prominently listed as an adviser on Halo’s Web site.

The Web site also makes some fairly bold and light-on-context performance claims, boasting that “the U.S. military accelerated pilot and sniper training by 50%” with similar techniques, and citing case studies with improvements of between eleven and thirteen per cent in various squatting and jumping exercises among early users. The company says it plans to submit research to peer-reviewed journals, but that hasn’t happened yet. For now, it’s sticking to a reliable Silicon Valley script, distributing the devices to high-profile athletes like the U.S. Ski Team and the Warriors.

The problem with this approach, if you’re interested in finding out whether the headphones actually work, is that top athletes are frantically eager adopters of any potential edge. Remember Shaquille O’Neal’s embrace of Power Balance, the plastic bracelets with little holograms that supposedly enhanced your natural energy field? (Recalling a game with the Phoenix Suns, O’Neal said, in a testimonial, “Three of my guys wore it, and I think we won that game by fifty-seven points. And I felt something.”) This isn’t because athletes, as a group, are idiots. It’s a rational response to the huge rewards that even an infinitesimal improvement in performance can bring—and a reflection of the curious links between mind and body. If I hand you a golf ball and say, “This has been the lucky ball today,” you’ll sink more putts than if I just say, “Here’s the ball,” as a famous study on lucky charms once demonstrated. That’s a consequence of what psychologists call self-efficacy: the belief that you’re going to swing the club (or shoot a thirty-foot three-pointer) accurately helps you do it less tentatively and, ultimately, more accurately.

For those with a scientific bent, trying to deliberately harness such effects smacks of charlatanism. But it shouldn’t, according to David T. Martin, the director of performance research and development for the Philadelphia 76ers. A few years ago, Martin and a colleague at the Australian Institute of Sport, where he worked for two decades before joining the 76ers, last year, wrote an editorial in the International Journal of Sports Physiology and Performance calling for sports scientists to stop disparaging placebo effects and focus instead on harnessing what he termed “belief effects.” He pointed out the curiously non-additive mathematics of ergogenic aids. Caffeine, sports drinks, and blood buffers, for instance, all produce one- to three-per-cent improvements in performance through well-understood physiological pathways. And yet, when you combine them, the over-all improvement is typically the same: one to three per cent. If one plus one plus one equals one, that suggests that all the aids are ultimately working on the same part of body—the brain.