The DEKA arm played a starring role in the historic events reported in the May 16 online edition of Nature magazine: Using BrainGate™, a neural interface developed by researchers at Massachusetts General Hospital, Brown University, and the Providence VA Medical Center in Rhode Island, two tetraplegic subjects – stroke victims suffering from paralysis in all four limbs and the torso – were able to move the arm to perform basic tasks using only their minds. One subject, a 58-year-old woman, was able to lift a bottle of coffee and serve herself a drink for the first time in 15 years.
How is a tetraplegic able to lift a bottle and drink? David Rosler, who manages the neural interface work at the Providence VA Medical Center, explained how the system works. A tiny electrode array, the size of a baby aspirin, is implanted in the brain just beneath the skull, with electrodes contacting the part of the motor cortex that controls the arm.
“When we bring our participants into the BrainGate trial,” said Rosler, “our software is capable of detecting the firing patterns of neurons associated with specific motions. So at the start, we show them a 3-D cursor going up and down, left and right, and diagonally on a screen. We monitor the neurons that fire and their firing rate, and our software allows those patterns to be built into the computer – it calibrates itself, so to speak. It says these neurons firing means you’re moving right. These neurons firing means you’re moving left.”
With this programming in place, the motor cortex is then linked directly to the arm – a complex process that involves further adjustments, filtering, and fine tuning. “We’re still at the early stages of this now,” Rosler said. “The degrees of freedom we’re investigating aren’t to the level of fine motor skills … but it’s a nice beginning to getting us where we want to get to.” The DEKA arm is currently in its third generation of development.
The modular prosthetic limb created by Johns Hopkins University’s Applied Physics Laboratory allows more freedom of movement for upper limb amputees. Here, Air Force Tech. Sgt. Joe Deslauriers picks up a ball using the new prosthetic. Photo courtesy of Johns Hopkins University
Another DARPA-sponsored product, the modular prosthetic limb (MPL), was developed by Baltimore’s Johns Hopkins University Applied Physics Laboratory with participation from nearly 30 other organizations. With more funding and development time than the DEKA arm, the MPL was designed to do everything a human arm and hand could do – to move every joint independently, offering 22 degrees of freedom.
On Jan. 24, 2012, Air Force Tech. Sgt. Joe Deslauriers, an ordnance disposal technician, became the first service member to use the MPL: rotating his wrist to grip a ball on the table, closing its fingers around it, and raising it into the air. Just four months earlier, Deslauriers had stepped on an IED pressure trigger in the dangerous Sangin District of Afghanistan’s Helmand province, triggering an explosion that blew off both his legs and his left forearm.
Because most military amputees injured in bomb blasts, like Deslauriers, retain intact nerves along the spinal cord that carry signals to the limbs, the first subjects to test the MPL did not undergo a direct electrode implantation in the brain; Deslauriers’ MPL was activated by surface electrodes attached to the surface of his skin, which picked up the brain’s electrical signals from muscle contractions, converted them into data packets, and relayed them as instructions to the arm.
Research into other means of activating the arm – injectable myoelectric sensors; muscle reinnervation (re-routing existing nerves to activate separate regions of a targeted muscle); and a direct brain connection – are ongoing at institutions such as the University of Pittsburgh’s Human Engineering Research Laboratories (HERL). Researchers are at work to broaden the variety and refine the fluidity of movements. They are also taking the first steps toward investigating the ability of an artificial limb to provide sensory input – to feel as well as move.
The MPL is the closest we’ve come to a human arm and hand; its wearers can throw a ball, shovel snow, golf, put on socks, and even cook. But DARPA’s research partners concede they’re nowhere near a true bionic arm with the motor and sensory capabilities of a real limb. If DARPA’s ultimate goal of replicating the human arm is realized – or even if a human arm is approximated more closely – it will enable more service members who have lost upper limbs to return to service if they choose.
In a profile published in the May 7, 2012 edition of Stars and Stripes, Deslauriers and his wife each took a pragmatic – but optimistic – view of the future. Though he’s able to drive, walk the dog, propel himself in his wheelchair, and hold his infant son, Deslauriers – who wants to serve six additional years in the Air Force and retire after 20 years of service – knows there’s still much he can’t do. Because of his determination and his help in refining the MPL, however, Deslauriers and the legions of scientists behind new robotic prosthetics are preparing a brighter future for servicemen and women – for all people – who suffer the loss of a limb.
This story was first published in The Year in Veterans Affairs & Military Medicine 2012-2013 Edition.