A significant amount of research and development has gone into creating sophisticated prosthetic limbs and learning how to effectively control them. But a major challenge for controlling a prosthetic arm is the communication between the device and the user’s phantom limb—the sensation that an amputated or missing limb is still attached.
In exploring ways to make it easier for users to control a prosthesis, researchers at the Johns Hopkins Applied Physics Laboratory (APL) found that giving users sensory stimulation enhanced the perception of their phantom hands and led to more reliable and repeatable muscle movement signals, which are used to control a prosthetic arm.
“We found that providing sensations of touch to the phantom hand of individuals with arm amputation improved the ability for them to not only feel their phantom hand but also move it,” said APL neuroengineering researcher Luke Osborn, PhD, the paper’s lead author. “This enhanced perception improved our ability to decode muscle signals, which are used to control a prosthetic hand, from the amputated limb.”
They also found that this improvement in phantom hand control only lasted for a few hours.
“We tracked one participant over time and found that his phantom hand sensory maps were stable—they didn’t move over a two-year period—and his ability to control his prosthesis was also largely stable over a one-year period,” said Osborn, who specializes in noninvasive nerve stimulation for sensory feedback, tactile sensor development, and upper-limb prostheses. “But, whenever we performed the sensory stimulation to his phantom hand, his ability to make movements with his phantom hand improved on that day.
The researchers are using a technique they are calling targeted transcutaneous electrical nerve stimulation (tTENS) to electrically stimulate small regions of the skin on the residual limb and create sensations of touch in the phantom hand.
“Because we see improvements in phantom hand movement as a result of restored touch sensations, we think this technique could help make it easier for users to control a prosthetic arm.”
Some study participants said that when their skin was electrically stimulated to produce tactile sensations, it was easier to perceive and move their phantom hand.
“As we started exploring this idea, we found that users were actually better at making complex hand gestures with their phantom hand after having received sensory stimulation earlier in the day.” EMG signals are recorded while users are cued with images to make specific gestures with their phantom hands. Hand movements are decoded from the EMG signal, which can then be used to control a prosthetic hand.
The results seemed to generalize to a variety of individuals, regardless of their amputation levels, which prosthetic limbs they use, or how long they’ve been using them.
Osborn and his team will continue exploring how restoring the sense of touch can improve prosthesis usage and overall functionality. “We hope to better understand which aspects of sensory stimulation are most influential in driving the changes we observed so that we can create customized rehabilitation strategies to promote long-term improvements in prosthesis control and sensorimotor rehabilitation,” he said.
The study, “Sensory Stimulation Enhances Phantom Limb Perception and Movement Decoding,” was published in the Journal of Neural Engineering.
Editor’s note: This story was adapted from materials provided by Johns Hopkins APL.
Image Caption: APL researchers have shown that giving arm amputees sensory stimulation enhances the perception of their phantom hand and leads to more reliable and repeatable muscle movement signals, which are used to better control a prosthetic arm.