For years, scientists have been exploring how we can use signals from the brain to control prosthetic limbs. Usually, this work is focused on restoring motor function to people who have lost an arm or a leg, but new research from Japan shows how the same technology can also be used to augment existing human capabilities.

Engineers from Kyoto’s Advanced Telecommunications Research Institute have demonstrated how people can be taught to control a third robotic arm with their brains, even using the limb to multitask. As described in a paper published in the journal Science Robotics today, eight of 15 test subjects were able to successfully balance a ball on a board with their hands, while grabbing a water bottle with a brain-controlled robot arm.

It’s multitasking using a third robot arm, but movement is limited

Although this may sound like something out of science fiction, it’s important to stress that the functionality of this third arm is extremely basic. The prosthetic moved along a predetermined path and performed only a single gesture: closing and opening its hand. Similarly, the brain-machine interface used to control the arm is not some magical mind-reading device. It’s a cap fitted with electrodes that measure electrical signals produced by the brain. In this case, participants were asked to imagine opening and closing the robot hand. The scientists recorded this signal, and turned it into an instruction for the robot arm.

“What we’re measuring is leakage from the brain’s electrical activity,” Shuichi Nishio, one of the researchers involved in the study, tells The Verge. “We have to tune [the brain-machine interface] for each participant; selecting the right electrodes and frequencies.”

Even with these limitations, though, it is very interesting work. As Nishio and his colleague Christian Peñaloza point out in their paper, it seems to be the first time supernumerary limbs have been controlled using the human brain. Usually such prosthetics are operated using joysticks or, if connected directly to the human body, electrical signals from muscles.

Past research in this area gives some clue as to how extra limbs might be used if they became common in the future. This concept device from MIT, for example, gives users two extra robotic “arms” that are worn as a backpack. The creators thought these arms could be useful in manufacturing; helping to hold tools and parts, or bracing a worker’s body if they’re squatting in one place for an extended period of time. If such robot arms could also be controlled by the brain, they could become a seamless extension of the body.

For Nishio and Peñaloza, supernumerary limbs might augment more than just our physical capability — they might improve our brains, too. In their paper, the pair noted that during the multitasking challenge, participants’ performance split into two distinct groups: those who were good and those were bad, with hardly anyone in the middle. This was in contrast to performance when individuals were asked just to control the robot limb by itself. In this single-task challenge, all participants did about the same, performing pretty well.

This difference, say Nishio and Peñaloza, suggests some people are just better at multitasking than others. And if that’s the case, then maybe multitasking is a skill that could be improved by using these sorts of brain-controlled devices. “By operating this brain-machine interface, we have an idea that we may be able to train the brain itself,” says Nishio.

This has yet to be proven, but the pair hope to work on the idea in future tests. After all, if you can learn to control three arms, then surely controlling two is child’s play.