They're walking the walk

Posted by Sam Maddox in Research News on September 30, 2015 # Research

Paraplegics are on their feet. Walking the walk. Seems we are hearing that a lot lately. Let’s look at two high profile stories, two very different approaches, both reported in the medical literature in September.

Mark Pollock
Mark Pollock practices walking with trainer Simon O'Donnell. (Courtesy of Mark Pollock)

Earlier in the month, Irishman Mark Pollock, blind at 22 and paralyzed 11 years later, became the first person with chronic, complete paralysis to voluntarily move his legs to facilitate ambulation, using an Ekso exoskeleton and non-invasive spinal cord stimulation. Typical headline, from the LA Times: “Paralyzed man walks with help of robotic exoskeleton at UCLA.”

Pollock, who is a member of the Reeve Foundation Board of Directors, said “ ... standing and walking with the [spinal] stimulation is like moving from a standard vehicle into the sports version. It felt like my legs were coming alive.”

Spinal cord stimulation is a story we have covered many times. The idea is that the spinal cord, even years after injury, and without input from the brain, retains what scientists call “automaticity.” In other words, there are spinal nerve networks that are apparently awakened by the stimulation. This is the basis for the work by Susan Harkema in Louisville that showed how four paraplegics implanted with epidural stimulators regained significant function. That in turn is the science behind The Big Idea, the Reeve Foundation bid to implant 36 more patients with stimulators.

In Pollock’s case, the stimulation was not implanted. It was applied directly to his skin, using an experimental device (NeuroRecovery Technologies) at the area of the lumbar spinal cord. Pollock also used a drug that stimulates the spinal cord. Using the exoskeleton, the combination enabled him to assist the robot in moving his legs; the data showed he was actively flexing his left knee and raising the left leg. OK, maybe it’s not quite right to call it walking, but he clearly fired up and controlled his body’s stepping system.

As the spinal cord responds by initiating muscle movement, the Ekso's sensors and motors adjust to reduce stepping power. The scientists suggest that in the future, such a device will assist but will not completely take over -- the robot will do less and less as the user does more and more.

The Pollock results, sponsored in part by the Reeve Foundation, were presented to the IEEE Engineering in Medicine and Biology Society (Noninvasive Reactivation of Motor Descending Control after Paralysis) by Reggie Edgerton, the UCLA scientist who was also a principal author for the Louisville epidural stimulation studies. He’s not making bold claims, but sees a role for robotics and rehab: “It will be difficult to get people with complete paralysis to walk completely independently, but even if they don’t accomplish that, the fact they can assist themselves in walking will greatly improve their overall health and quality of life.”

Pollock continues working with the NRT system in Dublin. Meanwhile, Edgerton’s group is currently running a clinical trial at UCLA to further refine the noninvasive stimulators.

Brainwave Breakthrough?
OK, now comes the report from UC Irvine: The feasibility of a brain-computer interface functional electrical stimulation system for the restoration of overground walking after paraplegia. The entire paper is available online.

Locomotor Training
Photo: King et al. Journal of NeuroEngineering and Rehabilitation 2015

This is about Adam Fritz, 26 at the time of the experiments, and five years post injury. He is a T6 para, complete except for some awareness of having a full bladder, from a motorcycle accident. The gist of the study is that Fritz learned how to summon up a brain signal via electroencephalogram (EEG) brainwaves; in turn, the brainwaves switched on a functional electrical stimulation (FES) device using 1980s technology to initiate stepping movements.

(Note the first major difference in the two approaches: FES applies current directly to muscle; spinal cord stimulation, e.g. in Pollock above, applies current to the spinal cord, which then responds by sending messages to the muscles).

Here’s one of the headlines, somewhat provocative, no?: “No Exoskeleton, No Brain Surgery: Paralyzed Man Walks Again Using Brain Waves."

Here’s what they did: Fritz wore a skullcap fitted with sensors to measure EEG waves and pass them via Bluetooth to a computer. He first used virtual reality program to learn how to make an avatar move. He had to master two modes: move and idle. So while he didn’t activate the particular part of the brain that would normally power the legs, he could nonetheless find the on-off switch. There is nothing novel about that; brainwave studies with paralyzed people are commonplace now, documented here, and with some pretty cool results.

What makes the UC Irvine experiment unique is that Fritz was able to use his brain signal to activate the stepping sequence programmed into a device called the Parastep.

Fritz also bulked up his legs as much as he could, using the Parastep alone. The device, typically accompanied by a wheeled-walker, generates sequences of electrical pulses that target peripheral nerves through surface applied skin electrodes. From Sigmedics, which has marketed the FDA Approved device since 1994:

Stimulation of the quadriceps muscles causes a contraction which results in knee extension, enabling the user to stand. Stimulation of sensory nerves in the lower extremities initiates a reflex contraction to flex the hip, knee, and ankle, lifting the foot off the floor; quadriceps stimulation then cycles on, to extend the knee in preparation for taking a step. The user controls stimulation through a user-friendly keypad on the stimulator unit or via control switches mounted on the electronically modified walker. The walker provides balance and stability to the user while standing and walking.

In the full experiment, Fritz didn’t use a walker; 60 percent of his body weight was supported by a harness device to prevent falls. But after some practice, after about 20 trials, he could cover about 12 feet. Walking? Well, call it what you will, he is ambulating, and he is deciding on his own when to step. It’s slow and not very elegant but nobody is saying this is practical; there is a lot of refinement to come.

So just what’s going on here? "Even after years of paralysis the brain can still generate robust brain waves that can be harnessed to enable basic walking. We showed that you can restore intuitive, brain-controlled walking after a complete spinal cord injury,” said study author Dr. An H. Do. “This noninvasive system for leg muscle stimulation is a promising method and is an advance of our current brain-controlled systems that use virtual reality or a robotic exoskeleton."

Coming next: your brain implant, and after that, how about an implanted FES system. "Once we've confirmed the usability of this noninvasive system, we can look into invasive means, such as brain implants,” said Dr. Zoran Nenadic, the study’s lead researcher. “We hope that an implant could achieve an even greater level of prosthesis control because brain waves are recorded with higher quality. In addition, such an implant could deliver sensation back to the brain, enabling the user to feel their legs."

From the paper:

... the cumbersome nature of the current noninvasive system makes its adoption for restoration of overground walking unlikely. This limitation can potentially be addressed by a fully implantable BCI [brain control interface] system, which can be envisioned to employ invasively recorded neural signals, such as electrocorticogram or action potentials, as well as implantable spinal cord stimulators or FES systems. Such a fully implantable system would eliminate the need to mount and unmount the equipment, such as an EEG cap, bioamplifier and a computer, thereby making the implantable system more practical and aesthetically appealing. Using an invasive system may also be the only viable approach to deliver cortical stimulation for restoring lower extremity sensation during walking.

In conclusion:

This proof-of-concept study demonstrates for the first time that restoring brain-controlled overground walking after paraplegia due to SCI is feasible. Further studies are warranted to establish the generalizability of these results in a population of individuals with paraplegia due to SCI. If this noninvasive system is successfully tested in population studies, the pursuit of permanent, invasive BCI walking prostheses may be justified. In addition, a simplified version of the current system may be explored as a noninvasive neurorehabilitative therapy in those with incomplete motor SCI.

The National Paralysis Resource Center website is supported by the Administration for Community Living (ACL), U.S. Department of Health and Human Services (HHS) as part of a financial assistance award totaling $8,700,000 with 100 percent funding by ACL/HHS. The contents are those of the author(s) and do not necessarily represent the official views of, nor an endorsement, by ACL/HHS, or the U.S. Government.