“Natural” use of the prosthesis

MADRID (EFE).— An international team of researchers has developed a device that seeks to “naturalize” the interaction between a person with an amputation and their prosthesis by promoting the two-way flow of information between the user’s nervous system and the robotic device.

Researchers from Imperial College London, the Medical University of Vienna and the University of Zaragoza achieved this feat, and the results of their work, which lasted several years, appear in the journal “Science Robotics”.

Scientists have found a way to control the contribution of spinal reflexes to the neural control of a prosthetic hand, and to achieve this they propose the use of nerve stimulation through localized vibration of the tendons associated with the motor task to be performed.

This stimulation modulates the excitability of certain spinal neural circuits, so that they contribute to integrating information about the state of the prosthesis (a bionic hand) for its control.

These spinal circuits are very important in sensory regulation and, as the scientists explain, although they are preserved intact in patients with an amputation, they are not used for the development of new neural interfaces for the control of prostheses.

The study provides promising results in this regard and shows how applying vibration to the tendons in a manner consistent with muscle activation significantly improves control of the prosthesis, with people even showing significant functional improvements for very specific actions, such as fine grip.

The scientific publication includes a video showing how a person with a prosthesis in his hand is able to “pinch” numbered dice from a box and overcome a small partition to transport them to another similar box and place them back in the same order.

Among the signatories of the work is the telecommunications engineer Jaime Ibáñez, from the Aragon Engineering Research Institute (I3A) of the University of Zaragoza, who stressed the importance of the interaction of an amputee with his prosthesis being “as natural as possible” and the interest in information flowing in both directions (from the person to the prosthesis and vice versa).

“I want to close my hand and the device closes my hand, but I would also like this prosthesis to feel things and transmit them to us in such a way that my nervous system incorporates and uses this information,” the researcher explained to EFE, who stressed that the main novelty of his technological development is that it is capable of promoting a natural interaction with robotic devices, which are already “tremendously complex” and have a great capacity for action, so that there is a true sensory and motor integration of the same.

Ibáñez stressed that despite technological and robotic advances to help amputees, the main challenge today is to ensure the most transparent integration possible between these devices and the nervous system of their users (the neural interface).

Currently, the primary way users get “feel” through their prosthetic limbs is through the user’s interpretation of certain sensory input, which is a far cry from the way natural limbs are controlled under normal conditions, which is largely done automatically, taking advantage of the advanced circuitry in the spinal cord.

“In our study we used the connections that already exist in the spinal cord and we took advantage of them to transmit information to the prosthesis, but we also managed to get the prosthesis to return information to us,” said Ibáñez, for whom improving this interaction and “naturalizing” these connections as much as possible can be decisive in helping users of these devices feel “in control” of their robotic hand.

In his opinion, there is still a long way to go – he began this research five years ago at Imperial College London – but he is also convinced that the technology, when it reaches a greater degree of maturity and passes all the testing phases, could also be replicated to other limbs and other prostheses.