cientists have rerouted a young quadriplegic man’s brain signals, allowing him to swipe a credit card, pour out a bottle, and move his fingers well enough to play Guitar Hero, they reported Wednesday in the journal Nature.
Reports of paralyzed limbs regaining motion always create excitement. But neurologists warn that this advance, while intriguing, is not going to help people with quadriplegia in the real world any time soon.
The patient, 24-year-old Ian Burkhart, trained on the neural bypass system for more than a year before he got the six hand and wrist movements down. And he can only move his hand while using the system in the clinic. Researchers on the team and elsewhere are working on wireless technology that would allow patients to use the system outside a lab and improve its durability.
Despite the limitations, Burkhart said being able to make movements with his hand that most people take for granted gave him a sense of hope. He was paralyzed after diving into a wave and being thrown into a sandbar the summer after his freshman year of college.
“I know firsthand what all was taken away from me when I had my injury,” said Burkhart, who retained some motion in his upper arms and shoulders after the accident. “For me, being in a wheelchair and not being able to walk isn’t the biggest thing.”
In a healthy person, the brain sends signals to muscles throughout the body via the spinal cord. Burkhart’s injury blocked that path, just as a bridge collapse would prevent drivers from crossing.
The neural bypass system acts as a detour.
As a first step, surgeons implanted a microelectrode array into Burkhart’s brain — specifically, an area of the left primary motor cortex tied to hand movements. A small port in his head lets scientists attach wires to that brain implant and stream Burkhart’s neural signals through a computer to a special sleeve he wears on his arm. The sleeve, dotted with 130 electrodes, helps convert those signals into muscle contractions to generate hand and wrist movement.
As Burkhart trained on the system, machine-learning algorithms refined how the signals were relayed from the motor cortex to the arm. As he learned how to use the system to trigger a specific hand movement, the system was simultaneously learning how to best decode his thoughts into the right impulses to prompt the correct arm muscles to contract.
The researchers had previously reported that Burkhart was able to hold a spoon and open and close his hand, but the advances documented Wednesday by a team from Ohio State University and Battelle Memorial Institute showed he had made progress on the types of motions that could help him in his daily life.
“What we’ve been working on is just trying to improve the functionality of the system, improve the amount that Ian can do,” said Nick Annetta, a Battelle electrical engineer and one of the paper’s authors. “Picking up a spoon was great, but we want him to do so much more.”
Other research groups have shown they can use the brain’s signals to control prosthetic devices, but the authors of the new paper said they were focused on helping people regain movement without the aid of robotics or mechanic exoskeletons. They also sought to minimize invasive procedures (other than the brain surgery) by using an external sleeve of electrodes instead of inserting the electrodes into the arm.
“The goal is to make it simpler,” said Dr. Ali Rezai, an Ohio State neurosurgeon.
But Robert Kirsch, a biomedical engineer at Case Western Reserve University not involved with the paper, said relying on electrodes on the skin’s surface may limit the technology’s strength.
Kirsch, who is part of a project called BrainGate, is working on another system designed to produce movement in patients with even more severe injuries than Burkhart has. He inserts electrodes into the arm, which he said allows for more selective muscle activation.
“It’s a nice study,” Kirsch said about the Nature paper. Creating movement is “a hard thing to do — I know because we’re doing it.”
But, he added, “surface stimulation is not very targeted.”
Other researchers not involved with the paper said the results were not all that different from responses other paralyzed patients have shown with different approaches.
The movements temporarily restored by such efforts aren’t totally fluid. That’s because even a seemingly simple hand and wrist motion rests on a complex choreography of different muscles contracting at precise times and at different strengths underneath the skin. Researchers still need to fine tune that choreography.
“It’s very difficult to figure out which set of muscles you need to activate to get a certain movement,” said Andrew Schwartz, a University of Pittsburgh neurobiologist who has worked on brain control of robotic prosthetics.
As excited as they were about Burkhart’s movements, the study’s authors acknowledged that they have a long way to go.
When they first saw Burkhart move his hand, Rezai said, “We said, ‘OK, now the real work starts.’”
Correction: A previous version of this story imprecisely characterized which researchers developed the neural bypass system.