A sensor that picks up nerve signals from the spinal cord could let people control a prosthetic arm by simply imagining the movement they want to make.
In tests using the sensor, which has to be surgically implanted, people were able to control a virtual arm on a screen with a larger range of movement than many existing prosthetics.
Prosthetic arms currently on the market are usually controlled by the user flexing muscles in their arm or chest. But there is a limit to how many commands can be mapped onto these muscle movements, which makes it difficult to do more intricate manoeuvres like pinching two fingers together.
A team led by Dario Farina, then at University Medical Centre Göttingen, Germany, instead developed a technique that interprets signals directly from motor neurons in the spinal cord. “In principal, we can reproduce all of the motion of a real limb this way, giving patients much greater dexterity,” he says.
Six people who are amputees from above the elbow tested the new sensor. To make the nerve signals strong enough for the sensor to pick up, they had some nerves associated with hand and arm movements surgically rerouted to muscles in their chest. This effectively amplifies the nerve signals, making them easier for the sensor to read.
The researchers then mapped these nerve signals to corresponding arm movements in people who have both arms. “We can use this to reconstruct the movement as if the arm were present,” says Farina. Then, all the user has to do is try to move the prosthetic as if it is their arm.
At this early stage of the work, the participants controlled a virtual arm on a screen rather than a real prosthetic. They were able to move the virtual prosthetic with greater freedom than has been achieved with muscle-controlled prosthetics.
Farina says that people who use prosthetic limbs capable of movement may abandon them if they are too difficult to control or do not offer a useful range of movement. He believes that making prosthetics controlled by nerve signals could be a better option.
“It’s a nice piece of biomedical engineering that allows really natural movement,” says Silvestro Micera at the Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland. Now that they have tested the concept, he says, the researchers need to show it working in a bigger study and with an actual prosthetic.
Journal reference: Nature Biomedical Engineering, DOI: 10.1038/s41551-016-0025
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