After Darth Vader lopped off Luke Skywalker's hand in the movie "The Empire Strikes Back," Rebel Alliance doctors installed a prosthetic that immediately moves and feels just like a human hand.
Science fiction is coming closer to reality at Johns Hopkins where researchers recently adapted a brain mapping technology to enable a patient to independently move individual fingers on a prosthetic arm just by thinking about it.
While such technology is years from practical application in patients, the breakthrough by biomedical engineers and physicians from Johns Hopkins University and its School of Medicine is the latest advancement in a growing field of research into mind-controlled movement of artificial limbs.
The Johns Hopkins researchers said their work, published this month in the Journal of Neural Engineering, is the first to accomplish such precise, individualized motion of the fingers and shows promise for one day providing amputees with prosthetics that more closely mimic the movements of real hands and arms.
While prosthetics have improved in recent years, they still can be bulky and hard to maneuver. The fingers on existing prosthetics move as one unit, or in unison, opening and closing together, like when grasping a soda can.
"We still have a bit of a ways to go before we get this in a practical clinical setting fully restoring the natural dexterity of people — but I think that day is coming," said Guy Hotson, an electrical and computer engineering graduate student at Johns Hopkins who was lead author on the study.
There are more than 100,000 people in the United States with amputated hands or arms that could potentially benefit from such prosthetics, according to the Amputee Coalition, an education, support, and advocacy organization.
"The mind control research is very cutting edge," said George Gondo, the coalition's director of research and grants. "It is really exciting to see improvement and to see actual results from the research."
Funded by the National Institute of Neurological Disorders and Stroke, the experiment used a modular prosthetic arm developed by Johns Hopkins Applied Physics Laboratory. Considered the world's most sophisticated upper-extremity prosthesis, the arm can perform almost all of the same movements as a human arm and hand.
The lab's research and development of the arm itself was funded under the Revolutionizing Prosthetics program of Defense Advanced Research Projects Agency with the intent of restoring limb function to wounded military members.
While building such a mechanically sophisticated prosthesis is possible, how to control it remains an open question.
That's where the Johns Hopkins researchers thought that brain-mapping technology known as electrocorticography could be used. But they needed a subject to whom they could apply sensitive electrodes directly to the brain.
Because the study involved opening the brain, the researchers needed to find someone already getting surgery for something else, so they recruited a young epileptic man undergoing brain surgery to stop seizures not controlled by medicine.
As part of the procedure, doctors placed electrodes on the patient's brain to help determine where his seizure originated, and then removed those parts of his brain.
The surgeons applied the same brain mapping technique to determine which parts of his brain controlled finger movement. A set of 128 electrodes sitting on a film the size of a credit card were placed on the parts of the brain that control hand and arm movement. Each sensor measured a millimeter of brain tissue.
The researchers then asked the patient, who was awake throughout the surgery, to move individual fingers. The computer program developed by Johns Hopkins engineers recorded the parts of the brain that were activated through electrical signals detected by the sensors as he moved each finger. (Researchers also tracked which parts of the brain responded to sensory input from the fingers by having the patient wear a glove with vibrating buzzers on each finger and measuring the subsequent electrical activity.)
Using the data collected from the patient's brain, the prosthetic arm was programmed to move particular fingers when corresponding parts of the brain were activated.
The prosthetic arm was then wired to the electrodes in the patient's brain and turned on. When he was asked to think about moving particular fingers, his brain activity moved the fingers on the prosthesis.
The patient was not an amputee and could control both of his arms. The metal and plastic prosthetic was mounted so that he could see it as it moved. The patient also did not have to do undergo any training to make the fingers move as patients in other studies have had to do.
The prosthetic arm still needs years of development, the researchers said. For one, it needs to connect to a computer running the software to work.
"Most of what is being done here is not built into the arm," said Dr. Nathan Crone, professor of neurology at the Johns Hopkins University School of Medicine who was part of the study. "Some day when this is used by patients it will probably require some faster computing and eventually it could fit in the arm. Right now it would require some kind of computing pack somebody would carry around. You need the computer near the arm in order for it work."
The Amputee Coalition's Gondo said motion-controlled technology has the potential to improve the lives of amputees — from the types of jobs they do, to their ability to live independently.
"The possibility for someone to be able to control their prosthetics like they would their natural limb is huge," he said.
At least half a dozen research institutions are testing mind-controlled prosthetics, Gondo said.
Even if the technology is perfected for mind-controlled prosthetics, cost remains a huge obstacle for widespread application. A modular prosthetic can cost half a million dollars, said Hotson, the lead researcher on this experiment.
"It will be interesting to see how and if they are able to bring any of this technology to market; that's always a challenge," Gondo said. "Particularly with upper limb prosthetics because it is such a small percentage of the population."
It could be years before mind-controlled prosthetics are even ready for commercialization, the Hopkins researchers said.
"We are not going to see this in patients right away," Crone said. "These are just the first steps toward that technology."