Upper arm prostheses that give their users a sense of touch have been developed in the past (see flashbacks below). These require careful surgical placement of electrodes near the remaining nerves within the stump and precise stimulation of said nerves. Now researchers at the University of Pittsburgh have achieved a remarkable feat of using existing spinal cord stimulators, usually used to treat chronic pain, to produce a sense of touch in the missing limbs of amputees. This can certainly be used to give upper arm prostheses the ability to produce sensory feedback, giving patients a natural way to feel what they interact with.
The new technique relies on existing implantation methods that are performed thousands of times each year in major hospitals. “What’s unique about this work is that we’re using devices that are already implanted in 50,000 people a year for pain — physicians in every major medical center across the country know how to do these surgical procedures — and we get similar results to highly specialized devices and procedures,” said Lee Fisher, the senior author of the study, in a press release.
Published in journal eLife, the researchers implanted Infinion electrode leads from Boston Scientific near the spinal cords, above the nerve roots that relay sensations from the arm, of four volunteers and connected them to Nano 2+Stim stimulators from Ripple, Inc. The stringy electrodes that have multiple stimulation points were then energized, in different spots, with signals that are usually sent to tackle pain. This immediately produced different sensations that seemed to come from the volunteers’ missing arms.
With a bit of experimentation and fine tuning, the researchers were able to reliably produce a feeling of touch in different parts of the phantom arms and hands. In three of the four volunteers, the researchers were able to generate highly localized sensations that were only felt in individual fingers or spots on the palm of the hand. “I was pretty surprised at how small the area of these sensations were that people were reporting,” said Fisher. “That’s important because we want to generate sensations only where the prosthetic limb is making contact with objects. The researchers followed their study subjects for a month following implantation, showing that even after natural movement of the electrodes the stimulation continued to do its trick.
This technology is applicable even for amputees that lost the entire arm and those that have seriously damaged nerves near the stump, as the stimulation happens at the spine. There’s still a good deal of work to make all this clinically practical, including actually implanting not just the electrode leads but the stimulators as well, reducing the amount of tingling and other stray sensations that the participants felt, and better targeting the affected nerves.
Here’s a video profiling one of the study participants and her experience with the new technology:
Study in journal eLife: Sensory restoration by epidural stimulation of the lateral spinal cord in upper-limb amputees
Flashbacks: World’s Most Advanced Prosthetic Now With Sense of Touch; Smart Electronics Bring More Realistic Sense of Touch to Prosthetic Devices; Case Hand Prosthesis With Sense of Touch Allows Amputees to Feel; Woman Using Powered Prosthetic With Sense of Touch in Everyday Life; Prosthetic with Sense of Touch Lets Patients Know Its Location; Electronic Skin for Prosthetic Hands Lets Amputee Feel Touch, Pain; Highly Compliant, Ultra Sensitive Electronic Skin to Give Prostheses a Sense of Touch