Sep 6, 2012

Man Walks With Aid of Brain-Controlled Robotic Legs


Walking on a treadmill is no great feat, unless your legs are being moved by a robotic device connected to your brain.

A new brain-computer interface allows a person to walk using a pair of mechanical leg braces controlled by brain signals (above), as reported on arXiv. The device has only been tested on able-bodied people, and while it has limitations, it lays a foundation for helping people with paralysis walk again.

“It’s an important step toward helping people with lower limb paralysis,” said biomedical engineer Matt Fifer of Johns Hopkins University, who has done similar work but was not involved with the study. “But there are lots of challenges still,” he said.

The new device — developed by researchers at the Long Beach Veterans Affairs Medical Center and the University of California, Irvine – is controlled by electroencephalogram, or EEG, signals generated by small voltage fluctuations in the brain. The method is completely noninvasive, as the signals are measured by a cap worn on the scalp.
The test subject in the study wore such a cap while standing on a treadmill inside leg braces known as a “robotic gait orthosis.” The subject would imagine walking or standing, and the device was taught to associate each brain activity pattern with the appropriate action. Then, whenever those patterns were encountered, the braces would start or stop walking accordingly.

The researchers also measured leg muscle activity by electromyogram, or EMG, for three conditions: active walking (with the robotic braces powered off), cooperative walking (aided by the braces), and passive walking (with the leg braces making all the movements).

Despite a couple of false alarms when the machine began walking when it wasn’t supposed to, the movement predictions were about 95 percent accurate. When the subject walked using the braces under brain control, the muscle activity appeared distinct from natural leg movement but similar to passive walking, suggesting no leg muscle control was necessary for robo-assisted walking.

Previous work has shown that EEG signals can be used to control a computer cursor or drive a wheelchair. The new device adds to a growing body of research aimed at restoring mobility after spinal cord injury or nervous system disease.

Of course, the robotic legs still need to be tested by people with paralysis. And the brain control can only toggle between walking or not walking, whereas a true walking aid would need to enable changes in direction and speed. But it’s a step in the right direction.

Video: Do et al. / Long Beach Veterans Affairs Medical Center & University of California, Irvine