Just because you can stimulate your brain with these headphones doesn’t mean you should

Taren Gesell got his first pair of brain-stimulating headphones in Kona, Hawaii in 2017 while at the Ironman World Championships triathlon. A company there had offered to sponsor him to use their product. A representative from the company told Gesell that if he used their headphones for 20 minutes before working out, it could improve his form, help him exercise more efficiently and generally make him a better athlete. Gesell, a triathlete and online creator who runs the YouTube channel and blog Triathlon Taren, was intrigued, but wanted to try the headphones out first. So, he took a pair home and added them to his workout routine. 

“I was not very impressed,” says Gesell. He says that at the time, the headphones, called the Halo Sport by the company Halo Neuroscience, “felt like a prototype.” In a video that Gesell made about the product in 2018, he notes the headphones were hard to connect, inconvenient to use and uncomfortable to wear. He decided not to take the sponsorship. 

But it wasn’t just that the product wasn’t user-friendly. More than anything, Gesell just wasn’t sure that these headphones worked, or even if they were really ready to be sold to consumers. And although Halo has made a new version of its product that has fewer technical problems, he still has his doubts. 

“I don’t know if I really felt noticeable improvement,” Gesell says. “There needs to be a little bit more data on it.”

Some research does suggest that transcranial direct current stimulation (tDCS), the type of brain stimulation that Halo uses, can induce real changes in brain function. This could translate to improved motor performance — for instance, a 2019 review of recent studies found that tDCS appeared to improve upper arm coordination. Although tDCS appears to help with motor skills, much of the research Halo itself cites is preliminary — testing tDCS on small groups of people over relatively short periods of time. 

tDCS is also being clinically tested as a medical treatment for conditions like multiple sclerosis and Parkinson’s disease, as well as an aide in stroke recovery. So far, the FDA hasn’t approved tDCS as a medical treatment. Even with the early promise of some clinical trials, it’s unclear what the long-term effects of tDCS might be. The potential of tDCS as a medical treatment also raises ethical, practical and safety questions about its use in products like Halo. As these clinical trials and new products bring tDCS into the mainstream, the answers to these questions will become increasingly important for the future of this technology. 

“It’s promising, but it’s still very much in the early days,” says Sheena Waters, a neuroscientist at University College London, of tDCS technology. Scientists like Waters also emphasize that although the technology may have great potential, more research needs to be done to ensure its safety and effectiveness.

Fire When Ready — Or When Stimulated

Transcranial direct current stimulation may seem futuristic, but it is surprisingly simple. And unlike some brain stimulation technologies, very little current from the stimulating device actually reaches the brain.

“Only a small fraction gets in,” explains Waters. Electrodes, which direct electrical current into a non-metallic substance, help stimulate the part of the brain associated with a specific function the user hopes to affect.

But the tDCS doesn’t directly impact the brain’s electrical activity. Instead, tDCS is thought to either increase or decrease the excitability of nearby neurons, depending on the type of stimulation used.

For instance, a tDCS treatment for epilepsy might aim to “calm” the brain by reducing neuron excitability, while a form of tDCS aimed at inducing neuron excitability is used in products like Halo to stimulate the portion of the brain associated with muscle memory.

“Your neurons are always resting at a certain threshold,” says Danny Holzman, Halo’s Neuroscience business partner manager. Neurons, Holzman says, tend to have a certain electric charge when they aren’t active, which is usually very negative. More negative neurons are less likely to fire. But he says the stimulation that Halo uses makes these neurons’ resting charges, or potentials, more positive, causing neurons in the stimulated region to become more excitable.  

“It doesn’t actually force neurons to fire, but it raises that potential,” Holzman says.

A Novel Medical Treatment

For decades, researchers have been trying to determine if tDCS can be an effective medical treatment. In many ways, it would be an ideal treatment: It is probably the safest method of brain stimulation available, says Leigh Charvet, a neuroscientist at New York University whose lab investigates how tDCS might be used to ease debilitating symptoms in patients with multiple sclerosis and Parkinson’s disease.

“Along the way, the longer you have the illness, the more symptoms you accumulate just day to day,” Charvet says. So far, she says, the results of her research seem generally positive. Although a 2018 report on two of her lab’s studies, which used tDCS to treat fatigue in multiple sclerosis patients, yielded only modest results. Of the people who received the tDCS treatment, 20% experienced significantly reduced fatigue, versus 10% of those who received fake stimulation. However, in the second study 36% percent of people responded to the treatment, while no one in the fake stimulation group had a notable response.   

London’s Waters also hopes her research could have medical implications. Using a piano-like keyboard that detects subtle changes in movement and pressure, Waters found in a 2014 study that tDCS use was associated with learning piano-playing movements faster — both simple sequential movements and those that involve more than one part of the body at once. But although Waters says research like hers provides some indication that this technology is effective, she cautions against making any generalizations based on her research.

“The study is just one snapshot,” she says.

Despite this, Halo cites Waters’ research as evidence that its product can enhance not only athletic, but also musical performance. While Waters notes that Halo cited her research appropriately, she says she does not support tDCS commercial products because the effects of tDCS on healthy patients are still not completely understood. Instead, Waters hopes tDCS might one day be used to help patients recover from strokes.

The Best of Both Worlds

Halo, meanwhile, is running its own clinical trials to see if its headphones could be used in stroke recovery. In a February 2016 blog post, the company announced that it would work with the Medical University of South Carolina on these trials. The Medical University of South Carolina has run two trials using tDCS for stroke recovery since 2016, according to public records. Results are not publicly available, but in February, the university started recruiting people to be part of a larger trial. This might mean the initial results have been promising.

Halo’s website makes clear that the device is not for medical purposes, although Halo’s Holzman says the product “isn’t really different than a medical device.”

Although Halo doesn’t currently market its headphones as a medical treatment, other smaller companies have no such qualms. Since the early 2000s, when the first formal scientific studies on tDCS in humans showed some benefits, several companies have popped up selling DIY-style tDCS devices — basically batteries with wires and electrodes that can be taped to the head. A website called Total tDCS even boasts a catalog of tDCS “montages,” which are different configurations of electrodes, some of which the website claims help treat anxiety, depression, and chronic pain. 

Direct Cause for Concern?

Consumers should be wary of tDCS devices even if they aren’t marketed as medical treatments, researchers in the field say, including Sheena Waters. 

There’s very little data on how long-term use of tDCS could affect the brain, according to Waters. Most studies, including hers, only study the effects of tDCS over a few days, while other studies last a few weeks. But consumers could be using tDCS products for many years. Asked about this, Halo’s Holzman said he was aware of some longer-term research, but did not provide details.

Current research also can’t definitively characterize how tDCS affects the brain, says Michael Nitsche, a neuroscientist at the Leibniz Research Centre for Working Environment and Human Factors in Germany. In a recent study, Nitsche and his collaborators used a type of tDCS that should inhibit neuron activity, which it did at both lower and higher electrical currents.

But to the researchers’ surprise, the middle current level unexpectedly excited neurons, says Nitsche. His results highlight how much is still not understood about tDCS and the brain. Nitsche also points out that customers would not be satisfied with an unexpected result from a tDCS product.

“I won’t be very happy if I have a 50% chance [of getting better], and a 30% chance of getting worse,” he says.

Despite this risk, Halo seems to be growing as a company. The company indexing website Growjo estimates Halo’s yearly revenue to be around $11.3 million, although their earnings aren’t publicly available. 

Seeking to expand its market, Halo recently came out with new headphones that are less expensive: around $400 instead of $700. The new model also incorporates Bluetooth wireless tech (Halos also function as normal headphones) and feature electrodes that are easier to connect.

Practice Makes Perfect

Most researchers in the field agree: tDCS is still in the early phases of research. Studies so far have been quite small, so it’s possible that tDCS doesn’t work or could even be harmful, as Nitsche and Waters point out. That uncertainty doesn’t seem to be discouraging Halo customers, however.  

Daniel Auner, a professional violinist from Vienna, came across Halo several years ago and now uses it to help him practice and prepare for performances. After some initial doubts, Auner says he regularly uses the product, especially when he is short on time. He says it helps him feel more focused during practice time and more on top of his playing during concerts. He also says that he thinks the technology, which effectively reinforces muscle memory that a person is already developing, is especially well suited for practicing a musical instrument.

Being strategic in his practicing is one reason why Auner thinks Halo works well for him. He also freely acknowledges that some amount of the benefits he experiences may be due to the placebo effect, in which a person sees positive effects of a treatment because they expect to. But even if some of Halo’s influence is due to this effect, its use raises ethical questions. For instance, pushy music teachers might want students to try Halo, but little research has been done on the effects tDCS might have on the developing brains of children.

And if tDCS turns out to be completely safe and effective, that raises its own questions. “It’s in a way, of course, cheating,” Auner says. If this product really works, whether it’s used by an athlete or a musician to improve performance, that person “has a clear advantage.”