Tuned in (Image: Mads Perch/Getty)

WHAT’S on your mind? For £79, anyone can buy a headset that reads the electrical activity of their brain. It’s called an electroencephalogram, or EEG, and you can use it to control devices with the power of your mind. But there’s a drawback: they don’t work when the wearer is moving and they look silly, so no one wants to wear them.

The solution could be a kind of EEG system that does away with the cumbersome electrodes, annoying gels and wires of its predecessors, replacing them with a flexible electronic skin that conforms to the body. It promises to let us monitor our brains discreetly 24 hours a day, and can be worn continuously for two weeks, staying put whether you’re swimming, running or sleeping.

John Rogers at the University of Illinois at Urbana-Champaign led the team that built the device, which is so light that it sticks to the skin through van der Waals force – the same mechanism that lets geckos’ feet stick to surfaces. It only falls off when the build-up of dead skin beneath it makes it lose its grip.


Comprising just a small patch of gold electrodes on and behind the ear, it beats the existing tech, described by Rogers as a “rat’s nest of wires attached to devices that interface to the skin with tape and gels and bulky metallic objects”.

To test it, the team looked at their system’s performance in tasks that clinical EEG devices usually handle. For example, volunteers were able to spell out the word “computer” on a screen in front of them using their brains’ electrical activity.

Their stick-on EEG was wired up to a computer for the tests, but the team is working on wireless transmission of data and power, something they have already achieved in other devices.

The focus is on medical applications to begin with – “EEG is important in detecting seizures – particularly in premature babies,” says Rogers. But the fact that it can sit discreetly behind an ear means that all kinds of other applications are feasible. No one wants to wear a headset constantly, but applying a hidden electronic tattoo once every two weeks is more acceptable.

Although Hidden EEG can’t rival the precision of the keyboard and mouse from your desktop computer, it is good for controlling systems in a more passive manner. Instead, it might start a coffee pot brewing in the morning when your brain activity implies you’re waking up. Or, if the device reads that you’re in a highly focused state, it could tell your phone to silence any notifications.

It might start a coffee pot brewing in the morning when your brain activity implies you’re waking up

“What we need is to measure EEG unobtrusively, invisibly,” says Stefan Debener of the University of Oldenburg in Germany, whose lab has developed its own version of an in-ear EEG system. He says that in tests on his own system, half the subjects forgot they were wearing the sensors. “This is exactly what you want,” he says. “You want tech that merges with the user.”

Debener is working on a way to measure the attention of a hearing aid user through EEG, then tune the hearing aid in to the voice they are concentrating on. Modern hearing aids can already focus on a single source in a noisy environment, but with EEG, they would be able to detect what their wearer wants to listen to.

“The limitation of EEG so far has been that we didn’t have the technology to study the brain in nature non-invasively,” says Debener. “This is a huge limitation. It’s very hard to tell how decisions are made in complex environments. If you could do this with EEG on the street, driving a car, that would make a big difference.”

This article appeared in print under the headline “Digital tattoo behind the ear can read your mind”