“The work is really neat, and is a nice proof of principle in the animal,” Stein says. “But I’d need a little more evidence to be convinced it would be useful in a person.”
The researchers still have much to do before the EMG technique can be moved into humans. The rats have only been tested on a treadmill, rather than more varied terrain. And translating Gad’s feedback loop from a rat’s four-legged stance to the human’s two-legged one won’t be simple, since humans don’t use their forelimbs in a way that could predictably act as a trigger for walking.
The EMG trigger, Edgerton says, is just the start of determining how to put movement control back in the patient’s hands. “We want to see what kind of strategies could be used for a patient to be able to control when to turn it on and when to turn it off.” EMG electrodes are already being used to help amputees control prosthetic limbs: activating a particular muscle, in combination with an EMG wire, can signal a prosthetic arm to move up and down or a prosthetic hand to open and close.
“This isn’t particularly remarkable—yet,” says Eberhard Fetz, a biophysiologist at the University of Washington. “Triggering the hind limbs by using the activity of the forelimbs is new, and I would be interested to check back next year to see if they’ve been able to create a more dynamic, continually interactive interface”—one that could incorporate feedback from the EMG electrodes in the hind limbs to create a fully functional system.
Gad is already on the case. He believes there could be other ways to get people to trigger stimulation, whether it’s a switch controlled by hand or something more akin to the muscle-activated prosthetics. “This is the first effort in trying to develop an interface that would go with epidural stimulation,” Edgerton says. “[Gad] has developed a system so that the rat has control. It doesn’t necessarily know that it has control, but when it moves the forelimbs, the hind limbs are going to be turned on. The idea is to get the animal more in control of what happens.”