Project offers better control and new sensations in artificial arms and legs

In a partnership with Case Western Reserve University (CWRU) The Defense Advanced Research Projects Agency (DARPA) is working to tap directly into nerves in the arms and the legs to give soldiers direct control of prostheses and sensations of feeling.  The project is part of DARPA's Reliable Neural-Interface Technology (RE-NET) project.

Since 2000, more than 2,000 service members have received injuries that required the amputations of limbs, while another 2,600 had lesser amputations (such as the loss of a hand).  Of the soldiers who received electronic prosthetics most of them are cortically controlled -- or controlled by electrodes on the head/neck or headsets with built-in electrodes.

By contrast RE-NET's latest effort focuses on so-called "peripheral control", tapping into nerves in the remaining muscles in the limb stub to control the robotic limb and/or receive sensations from it.  The process uses flat interface nerve electrode (FINE).  The approach is dubbed "targeted muscle re-innervation" (TMR).

FINE electrode
An artist-rendered closeup of the flat interface electrode used for TMR.

Former Army Staff Sgt. Glen Lehman was injured in Iraq and participated in one study at the Rehabilitation Institute of Chicago (RIC).  Earlier versions of the technology relied primarily on cortical-routed electrodes; the latest version also uses peripheral control.  Sgt. Lehman demonstrates the gains in fine control in this video:

A second study at the CWU in Cleveland, Ohio restored a sensation of feeling using TMR.  

TMR muscle
An illustration of the TMR approach used to re-innervate a muscle and "feel" a prosthetic limb.

The re-innervation technique allow the wounded soldier to "feel" sensations in his fingertips.  This allowed them to rummage through and select objects from a small bag of items -- a capability not possible with current generation prosthetics.

Jack Judy, DARPA program manager for the RE-NET project is enthusiastic about the early successes of TMR.  He comments:

Although the current generation of brain, or cortical, interfaces have been used to control many degrees of freedom in an advanced prosthesis, researchers are still working on improving their long-term viability and performance.  The novel peripheral interfaces developed under RE-NET are approaching the level of control demonstrated by cortical interfaces and have better biotic and abiotic performance and reliability. Because implanting them is a lower risk and less invasive procedure, peripheral interfaces offer greater potential than penetrating cortical electrodes for near-term treatment of amputees. RE-NET program advances are already being made available to injured warfighters in clinical settings.

With the RE-NET program, DARPA took on the mission of giving our wounded vets increased control of advanced prosthetics.  TMR is already being used by numerous amputees at military hospitals. As the RE-NET program continues, we expect that the limb-control and sensory-feedback capabilities of peripheral-interface technologies will increase and that they will become even more widely available in the future.

The RE-NET project will continue with a series of studies through 2016.

Sources: DARPA, RIC

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