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Neural engineering

Neural engineering

Phantom limb movement controls a robotic arm

Experimental set-up

Prosthetic limbs are crucial to improve the well-being of people who have suffered an amputation, and have undergone astonishing advances with the recent development of robotic prostheses. However, the protheses technology has advanced faster than the control systems, which limits their actual use in “real life”. This fact is particularly relevant for amputees suffering above the elbow (transhumeral) amputations, which require complex prosthetic arms with several joints and hence, complex control systems.

To overcome the limitations of amputees at controlling their protheses, researchers have investigated systems that recognize patterns of electric signals from the muscle, known as myoelectric signals. One of these systems can recognize phantom limb movement (PLM) signals, which are voluntary contractions of the muscles in the remaining limb to move the amputated extremity. In fact, the researchers have already carried out some preliminary studies employing a prothesis that recognize these signals.

Despite these advances, no study to date has investigated a PLM-based prosthesis that’s able to decode signals in real time to carry out day-to-day activities. Therefore, a team from the CNRS and Aix-Marseille University, in collaboration with the Regional Institute of Readaptation Nancy in France, conducted a study in which two transhumeral amputees tested a complex robotic prothesis with a control system able to decode phantom limb signals in real time to complete simple real-life activities (Front. Bioeng. Biotechnol. 10.3389/fbioe.2018.00164).

Robotic prothesis

In this study, the investigators developed an algorithm that could recognize the PLM signals and reproduce them in a prosthetic arm. With this prototype, patients could carry out designated tasks in real time with very little training. The system is highly intuitive and the patients were able to perform the activities without difficulty, as the research team shows in this online video. In addition, the transmission of the signals did not require surgery, which is a particular advantage for the patient.

These observations are encouraging, since this represents a fast and reliable system to develop a new type of prothesis for arm amputees, who often give up on their prostheses due to their complexity of control. However, the system still needs improvement, since the patients took long times to complete the activities. Future adaptations will also allow the amputees to wear the prothesis, as in this study they were limited to a prothesis connected to an external system. In addition, the research team intends to work to better understand the PLM phenomenon to apply it in future advanced prototypes.

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