Frequently asked questions

How does a mind-controlled arm prosthesis work? What means TMR?

  • When is it an option to provide a mind-controlled arm prosthesis?
    "From today's perspective, a mind-controlled arm prosthesis is an option in cases with a high amputation level. Those include glenohumeral amputations (arm amputations including the shoulder joint) as well as transhumeral amputations (arm amputations above the elbow)."

  • How does a person control the mind-controlled arm prosthesis?
    "The user moves the prosthesis by imagining it, i.e. moving the phantom arm in his or her memory. The prosthesis recognises this intent and carries it out. In principle, this is the same processed used by people with natural arms."

  • But how does the prosthesis recognise thoughts?
    "In the brain, it is probable that each thought is formed as a spatial pattern of tiny signals between billions of neurons. It is considered to be proven that such signals are formed from the outer brain cells and routed to the spinal cord for an intended arm movement, for example. Thanks to targeted muscle reinnervation (TMR), the prosthesis can pick up these signals."

  • What exactly is targeted muscle reinnervation (TMR)?
    "TMR refers to the surgical re-routing of nerves that transfer signals from the spinal cord to the new target muscle. For a glenohumeral amputation, for example, nerves from the brachial plexus which originally supplied signals to the arm and hand can now be partially re-routed to the pectoral muscles on the user's left side. These muscles, which originally moved the arm before the amputation, would now serve as biological amplifiers for the signals from the re-routed nerves."

  • How do these signals reach the prosthesis?
    "Highly sensitive power amplifiers gently touch the surface of the skin in the chest region with their electrical contacts. The signals from the brain are pre-amplified by the pectoral muscles so that the power amplifiers can pick up the signals through the skin and transfer them to the prosthesis."

  • What happens to these brain signals once they reach the prosthesis?
    "The prosthesis contains a high-performance minicomputer. It analyses the signals using 500 million calculations per second and determines the movement being imagined in the brain. Control signals for the motors are calculated at almost the same time, leading to execution of the movement in the prosthesis in less than 80 milliseconds."

  • Which movements can the mind-controlled prosthesis make?
    "A total of three joints can be controlled with the mind-controlled prosthesis. The hand can be opened and closed, the wrist can be rotated inward and outward, and the elbow joint can be flexed and extended. Since these joints can be moved simultaneously, patients can make quick, targeted movements intuitively."

  • What kind of enhancements will the future bring for the mind-controlled prosthesis?
    "In the future, mind-controlled prosthetics will have more than three joints. A prototype with seven joints has already been tested in a laboratory setting. The sensory (afferent) fibres of the re-routed nerves will be used, not just the motor (efferent) fibres. This will be the gateway to a prosthetic hand that allows its users to feel objects with their prosthetic hand in much the same way they did before the amputation. I'm certain that this represents yet another quantum leap in the improvement of amputees' quality of life."

Science Center Berlin

Science Center Berlin
The technology showcase of Ottobock.
Science Center Berlin

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