Researchers called the advance the first demonstration of reaching and grasping by a brain-
controlled prosthetic arm. In recent years, other paralyzed patients have high-fived with a different robotic arm and moved a cursor around a computer screen simply by thinking about it.
While the scientists involved cautioned that it will be years before such devices will be widely available, they hailed the advance as a milestone.
“Things in this field are exploding right now,” said Andrew Schwartz, who is developing another thought-controlled robotic arm at the University of Pittsburgh and who was not involved in the work reported Wednesday. “You’re going to be seeing much more in the near future — much more natural movements, faster movements, approaching what normal [people] can do.”
In the new study, researchers implanted a tiny electrode chip — the size of a baby aspirin — into the brains of two patients. Both had suffered strokes in their brain stems that left them in a “locked-in” state. While their brains worked normally, connections to the muscles below had been severed, leaving them quadriplegic and unable to speak.
Placed on the motor cortex — a sliver of brain that controls movement — the chip listened to signals generated by the patients’ brain cells as they thought about moving their own arms. A computer read that signal, interpreted it and sent movement messages to the robotic arm.
“I just imagined moving my own arm, and the [robotic] arm moved where I wanted it to go,” the second patient, a 66-year-old man, told the researchers in response to questions submitted earlier by journalists. He can slowly communicate by moving his eyes as an assistant points to letters on a board.
A cable attached to the skull transmitted the signal.
“They’re basically plugged in,” said John Donoghue, a Brown University neuroscientist involved in the new work, which was reported in the journal Nature.
Ongoing work seeks to remove the cable, making the system wireless and more practical, Donoghue said in a teleconference with reporters.
The trials reported Wednesday took place last year. In them, the patients touched and grabbed foam balls on a table with two different robotic arms. The woman succeeded about half the time with an arm made by the company Deka as a prosthetic for amputees. With a second arm, made by the German Aerospace Center, she succeeded about 70 percent of the time. The male patient did even better.
“At the very beginning, I had to concentrate and focus on the muscles I would use,” the female patient, Cathy Hutchinson, told the researchers via assisted communication. But they said she quickly got accustomed to the process.
A team of brain scientists, engineers, mathematicians and computer scientists at Brown University, Harvard Medical School and elsewhere worked on the brain-computer interface — called BrainGate — for more than a decade. The National Institutes of Health and the Department of Veterans Affairs funded much of the work.
The key breakthrough: programming computers to interpret the brain signals as arm and hand motion.
The researchers did so by training the computers — and the patients. With the brain interface plugged in, the researchers moved the robotic arm and told the patients to imagine moving their own arm in the same way. The computer recorded the brain signals generated. Later, when the patients were asked to move the arm, the computer responded by tapping into the data bank of brain signals it had stored.
Despite her being paralyzed for 15 years, the woman’s brain still generated signals corresponding to hand and arm movement.
“This means the motor cortex continues to operate in what appears to be a normal way,” Donoghue said. “That allows us to tap into them even years after some event like a stroke or spinal cord injury.”
The Food and Drug Administration gave the researchers permission to study the BrainGate device as experimental, and they are collecting long-term safety data.
Researchers are encouraged that the brain chip in Hutchinson continued to work five years after it was implanted, although the signal it transmitted had weakened, probably because of scar tissue building up around the chip.
As the researchers tested her ability to pick up foam balls, they gave her the chance to grab a bottle of coffee and take a sip through a straw. She succeeded.
Said Brown University’s Leigh Hochberg, one of the scientists involved: “The smile on her face when she did this was something that I and . . . our whole research team will never forget.”