Doctors couldn’t fix Ian Burkhart’s spinal cord injury. So engineers figured out a way around it.
Their “neural bypass” system uses a brain implant to record the electrical signals generated when Burkhart tries to move one of his paralyzed hands. Those signals are decoded by a computer and routed to an electronic sleeve that stimulates Burkhart’s forearm muscles in precise patterns. The result looks surprisingly simple and natural: When Burkhart thinks about picking up a bottle, he picks up the bottle. When he thinks about playing a chord in Guitar Hero, he plays the chord.
Yet the technology at work is far from simple. The achievement, reported today in Nature, caps a decade of research on brain-computer interfaces (BCIs) for paralyzed people. In 2006, a quadriplegic man used a brain implant to control the movements of a computer cursor; six years later a quadriplegic woman used an implant to control a robotic arm, which she used to independently bring a coffee drink to her lips. Meanwhile, other researchers have investigated different ways to control paralyzed limbs with electricity, using stimulating electrodes to jolt muscles into action.
Today’s announcement marks the first time these two technologies have been combined to help one human. BCIs had previously shown progress “with cursor control, using a computer, being able to operate devices, and even prosthetic arms,” says Chad Bouton, a study coauthor who researches bioelectronic medicine at the Feinstein Institute on Long Island. “But no one had restored any movement to the arm. We decided to take it to that next level.”
Burkhart broke his neck during a beach vacation in 2010 when an ocean wave drove him down into a sandbar, breaking his neck. He was paralyzed from the fifth cervical vertebrae down, meaning that he could move his head, neck, and upper arms, but nothing else. “For me, being in a wheelchair and not being able to walk isn’t the biggest thing,” he said at a press briefing yesterday. “It’s the lack of independence I have, because I have to rely on other people for so many things.”
By demonstrating that Burkhart could use the neural bypass for functional movements like swiping a credit card, the researchers offer hope to paralyzed people seeking renewed autonomy. Right now, the experimental system can only be used in the lab. But the long-term goal is to build a system that’s safe and simple enough for people to use at home.
Here’s how the neural bridge works. The implant’s array of 96 electrodes record the electrical activity when brain cells “fire” in a particular part of Burkhart’s motor cortex, which is active when he imagines hand movements. But understanding the data from the implant is a monstrously difficult task. Each of the 96 electrodes measures activity 30,000 times per second, so there’s a great deal of noise obscuring the discrete signal that means, for example, “flex the thumb.”
Burkhart attended up to three sessions weekly for 15 weeks to train the system in understanding his brain signals. First he would watch an animated hand on a computer screen flex its thumb, and he’d imagine making that movement while the implant recorded his neurons’ activity. Over time, a machine-learning algorithm figured out which pattern of activity corresponded to a thumb flex.
Now that the system recognizes the signal, it can generate a pattern of electrical pulses, mimicking the pulses the brain would typically send down an undamaged spinal cord and through the nerves. The pulses go to the sleeve on Burkhart’s forearm that consists of 130 electrodes, which stimulate specific muscles to flex the thumb. The researchers carried out the same process for many different motions of his fingers, hand, and wrist.
While other research groups are experimenting with wrapping implanted electrodes around the nerves themselves to stimulate muscles, Bouton’s team chose to use non-invasive electrodes to stimulate the muscles through the skin. Bouton says they made that decision to keep the system simple and make it adaptable to home use. The electrode sleeve “could be part of a shirt in the future,” he says.
Making a home-use model of the neural bypass still requires some big technical leaps, however. To use the current system, Burkhart must attach a cable to the small “pedestal” that juts out of his skull. The researchers want to develop a way to wirelessly send the implant’s data to a computer, but the sheer amount of data being transferred poses a problem. “About 1 gigabyte of data comes off Ian’s brain every three minutes,” says Nick Annetta, a study coauthor from Battelle Memorial Institute in Columbus, Ohio.
Researchers are also working to keep the implant functional over many years. The brain treats it as a foreign body and can “encapsulate” the electrodes as a protective measure, preventing them from recording signals from the neurons. In the two years since Burkhart received his implant, some of the 96 electrodes have stopped transmitting data, the scientists say. But enough are still operating to keep the system functioning.
But having come this far, the research team is optimistic that the next challenges will be overcome in due course. And for all the technological prowess required, Burkhart says the most exciting part is how the gear could eventually fade into the background of his life. Burkhart adds that regaining use of his natural arm appeals to him much more than using a BCI to control a robotic prosthetic arm. “It allows me to function almost as a normal member of society,” he says, “and not be treated as a cyborg.”
Check out the video below to see the system in action.