Prosthetic arm takes alternate route to mind control

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The 'bionic reconstruction' procedure involves reading electrical activity from transplanted muscle to control a bionic arm using thought (Photo: The Lancet)

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Researchers from the Medical University of Vienna have developed a technique that allows amputees to control a robotic prosthesis with their mind when there's no neural connection left to exploit between the brain and the part of the hand that remains. Called "bionic reconstruction," the procedure was applied to three patients who were able to successfully use the prosthesis to undertake routine activities, thereby improving their quality of life.

While we've seen thought controlled prosthetics that use an amputee's own nerves to interpret signals, creating a mind-controlled prosthesis for those whose mind has been severed from their hands is extremely challenging. This happens when the network of nerves called the brachial plexus, (which begin in the neck and spread to form the nerves controlling movement in the shoulder, forearm and hand region), are severely damaged. Sufferers of brachial plexus injuries have effectively experienced an inner amputation – their hand is no longer connected to their brain.

"The connection between the brain and the hand has been lost, as some of the nerves supplying the hand have been pulled out of the spinal cord at the level of the neck," Aidan Roche, a bioengineer at the Medical University of Vienna and the study's co-author, told Gizmag.

Brachial plexus injuries can be caused by the severe trauma the body experiences in collision sports like rugby, or high speed collisions like motorcycle accidents. Taking advantage of the fact that the patients still had the ability to use their shoulder, elbow and forearms normally, the team team was able to find alternate neural signals that could be used to control the prosthetic hand.

Moving the shoulder and elbow, produces a flicker of movement in the forearm that's caused by slight contractions in the muscles. The researchers recorded this flicker via skin sensors to enable the movement to be used to open the bionic hand. To create an additional signal that would get the bionic hand to close, the team had to transplant a muscle from the patient's thigh into the forearm.

"Once this muscle is connected with the nerves in the forearm, it is able to amplify or boost the nerves signal, much like turning the volume up on a radio," Roche told us. "Using another sensor we can get a second signal which can tell the prosthetic hand to close. A combination of these signals will rotate the hand at the wrist."

Before undergoing elective amputation, the patients spent nine months in cognitive training, to activate their muscles and maximize these signals to control a virtual hand. Once they'd mastered that, they underwent training with a prosthetic hand attached to a splint-like device fixed to their non-functioning hand. The final bionic reconstruction procedure involved amputating their existing hand and replacing it with a robotic one.

"The scientific advance here was that we were able to create and extract new neural signals via nerve transfers amplified by muscle transplantation," says Professor Oskar Aszmann, the lead scientist on the team. "These signals were then decoded and translated into solid mechatronic hand function."

The speed and strength of movement is proportional to the strength of the muscle contractions. Measuring hand functionality using the Southampton Hand Assessment Procedure (SHAP), where normal hand function is considered to be equal to 100, and no hand function is zero, the patients had a score of 65.3 after bionic reconstruction.

The procedure allowed all three men to accomplish various everyday tasks they had not been able to achieve since their respective accidents. These included picking up a ball, pouring water from a jug, using a key, cutting food with a knife, or using two hands to undo buttons.

The researchers plan to apply the technique next to patients who have experienced different injuries, such as crush injuries or mangled limbs that have led to a functionless hand or leg. They are also examining ways to decode the muscular signals, using advanced pattern recognition methods, to achieve more intuitive control of the prostheses.

The study detailing the technique was published in The Lancet.

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