SCIEPRO / SCIENCE PHOTO LIBRARY / WIRED

Take a nine-volt battery, a couple of sponges and some saline solution, and you can change your life. That’s the alluring promise of transcranial direct current stimulation (tDCS), a non-invasive mind-altering technique that’s gaining a cult following among athletes, budding musicians, and now even business leaders.

The process involves running a small current through the brain via electrodes placed on the scalp and forehead. It’s been claimed that it can improve focus, boost endurance, treat depression and even reduce prejudice. Consumer headsets are widely available to buy online, and there’s an active DIY community building their own brain-altering devices at home.


Inevitably, the wellness industry is also getting in on the act. At the SHA Wellness Clinic on the southern coast of Spain, business leaders and high-powered diplomats come to unwind and relax with healthy food, spa treatments, and brain zapping. “They’re decision-makers and people who have very stressful lives and are aware that they need to reset themselves,” says SHA vice president Alejandro Bataller. “They come to learn more about themselves so they can enjoy optimal vitality and brain activity, and therefore productivity.”

But there are doubts over the effectiveness of tDCS, and fears that people could do themselves long-term damage with unlicensed or home-made devices. There’s still a lack of robust evidence that tDCS, and the related transcranial alternating current stimulation (tACS) actually work. “The field in general is plagued by low quality research and publication bias,” says Vincent Walsh, a cognitive neuroscientist at University College London. Experiments have had small numbers, and poor controls that don’t do a good job of eliminating placebo effects. “When we look at tDCS, people have jumped the gun, they have made claims to sell these things to people that are not based on the literature,” Walsh says.

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In theory, tDCS works by changing the electrical excitability of neurons in the brain – making them either more or less likely to fire and creating the desired effects. But in a recent paper, Walsh and colleagues Beth Parkin, Mayank Bhandari, and James Glen found that the physiological effects supposedly driving this process don’t actually occur in the form of tDCS most frequently used in research. Walsh says this has led him to believe that the contradiction between his group's finding and the observed literature is "much worse" than just publication bias (the tendency to only publish positive results), and that people are actively selecting data.

Other brain-stimulation technologies, such as transcranial magnetic stimulation (where a powerful magnetic field is passed over the brain) are tightly regulated because of their potential to mess with important neural functions. But tDCS is the wild west. The r/TDCS sub-reddit has more than 12,000 users, who swap tips on how to make their own tDCS kits, and advice on montages – combinations of different electrode placements – to achieve different effects. Some DIY users report positive results (“Best Sex ever after TDCS session with GF”), but others experience only headaches, skin burns and a persistent metallic taste in the mouth. More serious risks include sudden mood swings and seizures.


In 2014, psychologist Nick Davis at the University of Swansea published a paper calling for “extreme caution” in using tDCS and highlighting a number of problems, including a lack of knowledge about long-term side-effects, a lack of clear dosing guidelines, and a dearth of research about how tDCS might impact children.

That hasn’t stopped a wide range of consumer devices being made available for sale, supposedly offering a safer alternative to hooking yourself up to a battery (never the mains) at home. The Brain Driver, available for £120, boasts improved mood, better sleep and pain reduction, while the Foc.us Go Flow 4 offers the most powerful tDCS available anywhere for £199. The Halo Sport 2, which is aimed at athletes, does away with messy leads entirely and integrates its electrodes into a pair of over ear headphones, while the Humm patch sticks to the forehead like a cooling pack (it uses tACS, powered by alternating current), and claims to boost working memory function. “Each patch lasts 15 minutes and provides up to two hours of improved mental performance,” the company claims.

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Some of these devices say they’re clinically proven (others don’t bother) but none of them are marketed as medical devices. The sole exception to that is the Flow headset, launched last month in the UK and Sweden, which attaches to two points on the forehead and looks like something a window-fitter might use to remove a pane of glass. Made by Swedish company Flow Neuroscience, the headset has CE approval in the EU (and the UK), which means that it conforms to certain health, safety and quality standards, and which allows it to be sold as a medical device for the treatment of depression.


“There are a bunch of devices out there with a wellness perspective,” says co-founder Daniel Mansson, a clinical psychologist who first became interested in tDCS after reading an article about a brain stimulation headset aimed at gamers in this very title. “They don’t say that they treat anything, but we say that we treat depression.”

Flow aims to provide a pharmaceutical-free treatment for long-term depression, which is, in some cases, associated with lower neural activity in the left frontal lobe. The headset, which “stimulates and rebalances” neural activity in this area, is designed to be used in conjunction with an app that features video content, information and advice about sleep, diet and meditation. The company recently secured a £1.2m investment from private equity firm Khosla Ventures to fund clinical studies and support a rollout in the UK and EU.

A note on the Flow website warns that it should only be used by people with a medical diagnosis of depression, but no prescription is required to purchase the £399 headset. In the EU, new regulation coming into force from May 2020 will ban the sale of wearable devices that haven’t gone through the CE marking process that Flow has done – so by then, they could be the only choice for tDCS enthusiasts who aren’t quite brave enough to hook their brains up to a homemade brain stimulator. However, it’s fixed in a set, proven montage so there’s a limit to how much self-experimentation can be done. “With our device there’s a strict protocol,” Mansson says. “It’s like us coming home to you giving you a pill and saying you should take this at 12 o’clock.”

Mansson says the new EU Medical Devices Directive coming fully into force from May next year means that Flow had to demonstrate efficacy as well as safety to get a CE mark. But, Walsh argues that although being CE approved proves that the product isn’t dangerous, it’s not equivalent to NICE or FDA approval.

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He accuses the company of cherry-picking from the literature to show that its product is effective at treating depression, while ignoring more measured and negative randomised control trials and meta-analyses, as well as “individual differences, treatment resistance and depth of depression”.

Flow are working towards FDA approval in the US and is starting talks with the NHS to make the headset available on prescription. Mansson says they’re not interested in moving into the wellness space, occupied by many of the others. “We are a medical device company,” he says. “The most reasonable thing to do with this kind of technology is to keep it as a medical device.”

That won’t stop perfectly healthy people from being drawn in by the allure of hacking their way to happiness. The evidence remains thin, but even if it did actually work, there are questions over whether being able to improve our mood at the flick of a switch would actually really be desirable. The evidence from patients with deep brain stimulation, admittedly a much more invasive and drastic treatment than tDCS, suggests not.

An article in The Atlantic by Lone Frank, the author of The Pleasure Shock, recounts the story of a middle-aged American woman who was fitted with a deep-brain stimulator to help relieve chronic pain, along with a self-stimulator that enabled her to regulate the current herself – in the same way hospital patients can push a button to release more morphine. But pressing the button felt too good, and the woman did little else for the next two years, ignoring personal hygiene and her husband and children. “Finally, her family pressured her to seek help,” writes Frank. “At the local hospital, they ascertained, among other things, that the woman had developed an open sore on the finger she always used to adjust the current.”

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