Neuron activity associated with imagined movements could be used to control prosthetics Sam Hodgson/New York Times/Redux/eyevine

People who have had amputations can control a virtual avatar using their imagination alone, thanks to a system that uses a brain scanner.

Brain-computer interfaces, which translate neuron activity into computer signals, have been advancing rapidly, raising hopes that such technology can help people overcome disabilities such as paralysis or lost limbs. But it has been unclear how well this might work for people who have had limbs removed some time ago, as the brain areas that previously controlled these may become less active or repurposed for other uses over time.

Ori Cohen at IDC Herzliya, in Israel, and colleagues have developed a system that uses an fMRI brain scanner to read the brain signals associated with imagining a movement. To see if it can work a while after someone has had a limb removed, they recruited three volunteers who had had an arm removed between 18 months and two years earlier, and four people who have not had an amputation.


While lying in the fMRI scanner, the volunteers were shown an avatar on a screen with a path ahead of it, and instructed to move the avatar along this path by imagining moving their feet to move forward, or their hands to turn left or right. The people who had had arm amputations were able to do this just as well with their missing hand as they were with their intact hand. Their overall performance on the task was almost as good as of those people who had not had an amputation.

“Although the amputees’ performance is a little bit behind the control group, the big picture shows they are almost the same level, and still using the missing arm in their brain,” says Cohen, who presented the research at the IEEE EMBS Conference on Neural Engineering last month.

Because the system requires a person to be inside a brain scanner, it would not be possible to use it outside a lab. But Cohen thinks that a new technology called functional near infrared spectroscopy will make it possible to read the same brain signals with portable devices. This may lead to new ways for people who have had limbs removed to control prosthetic devices.

But Dario Farina, of Imperial College London, doesn’t think such a system is likely to be very useful for amputees. “There are alternative techniques that are far superior for prosthetic control,” he says.

The fMRI interface only distinguished four commands: forward, stop, left and right. Prosthetic controllers that work by detecting muscle signals at the stump of the severed limb can distinguish more commands, respond more quickly, and allow the user to control the force or speed.

Farina thinks Cohen’s system could be more useful for locked-in patients, who have no means of communicating except via brain signals. “For other types of patients, this is a good performance, which is promising,” he says.

Read more: Amputees control virtual prosthetic arm using nerve signals