A new therapy that stimulates the spinal cord directly allowed Rob Summers to walk again for the first time in 5 years.

In 2006, Rob Summers was the victim of a hit-and-run. The accident left him completely paralyzed from the chest down–unable, even, to wiggle his toes. But just weeks after beginning a new cutting edge therapy in which researchers electrically stimulated his spinal cord Summers was able to stand on his own, move his hips, knees, ankles and toes, and make stepping motions on a treadmill.

Summers’ long road to betterment began in October of 2007. Over the next 26 months he received 170 training sessions in which he was suspended over a treadmill by a harness while researchers manually moved his legs and feet. The physical therapy was not effective. During the course of 108 hours of step training and 54 hours of stand training, electrodes placed in Summers’ leg muscles showed no electrical activity related to the trained movements.

After the training failed, researchers attempted a cutting edge procedure to surgically implant an epidural electrode array over the lumbosacral segments of Summers’ spinal cord. The training sessions resumed, this time while injecting direct electrical current.

It was a breakthrough in rehabilitation therapy.

In the first weeks after surgery Summers could stand on his own, providing the initial lift himself. He can remain standing up to four minutes at a time, and up to an hour with occasional help. After a few months he was able to move his hips, bend his knees, ankles and toes. Today, with the aid of a harness and an occasional helping hand, he can lift and move his feet to make stepping motions on a treadmill.

The science team responsible for Summers’ incredible improvement was led by Susan Harkema at the University of Louisville and included researchers from UCLA and the California Institute of Technology. Recently published in The Lancet, the science behind Summers’ phenomenal progress takes advantage of the “smart” circuitry of the spinal cord. Kind of like being on autopilot, it controls our leg movements enough so that we can walk without thinking about it. We’re able to take a stroll through the woods and talk to our friend without the need to plan around every branch or rock. The spinal cord circuitry is so good at its job it doesn’t need input from the brain. It’s precisely how chickens are able to run with their heads cut off.

However the spinal cord is not entirely autonomous. To correctly control movement it requires continuous feedback from the legs and other parts of the body involved in the movement. Referred to as “task-specific sensory information,” these signals tell the spinal cord how weight shifts from leg to leg, for example, so that spinal circuits can transmit their walking commands in a precisely-timed, rhythmic manner. Changes in gait as you step over the branch will be read by the spinal cord and its output will adjust accordingly to keep you moving.

However, compared to healthy people, the activity of spinal neurons in paraplegics is decreased. Owing to the damaged spinal cord, the signals coming from the brain are less. The end result is a spinal network that is not responsive to task-specific sensory information–and a person that can’t walk. The epidural stimulation provided by Dr. Harkema and her colleagues substitutes that input from the brain. It “jump starts” the movement process and allows the spinal cord to combine the sensory input coming from the legs and direct the muscles and joints to move.

It’s easy to confuse the mechanism and think that the electrical stimulation might drive the movements directly, but that’s not the case. Indeed, the researchers point out that stimulation did nothing when Summers was sitting still even though they could measure electrical activity in the muscles. Only when he shifted his weight did the spinal cord network have “data” to work with, organize its commands properly, and cause Summers to stand up. The intensive training helped the spinal cord neural networks to “re-learn” the proper way to use sensory information to direct the muscle movements necessary for standing and for taking assisted steps. You can see the researchers' excitement in the video below as they watch Summers move his legs and stand on his own.

In addition to the returned mobility, some of the complications due to his condition showed improvement, including bladder and sexual function, and thermoregulation. These unanticipated benefits are thought to be due to the fact that the same spinal circuits that control movement also affect these functions.

Summers says the procedure has completely changed his life and that he believes the epidural stimulation will eventually get him out of his wheelchair.

The authors mention that the study was the first attempt at treating a paraplegic by directly stimulating the spine. Although Summer’s progress is amazing, there are several caveats. First, the study only included a single person–a particularly fit person. Also, although he is completely paralyzed, Summers is able to feel some sensation below his spinal injury level. The treatment has yet to be proven with the most dire type of patient–those with no sensation whatsoever below their spinal level of injury. Four additional subjects have passed FDA approval to participate in the study. We’ll be watching for their first steps with our fingers crossed.

There’s also room for improvement. The epidural electrode was originally intended for stimulation-mediated pain relief and had not been optimized for use in this study. Tweaking stimulation parameters may improve results. Also, earlier animal studies have showed that spinal cord stimulation in conjunction with drug interventions can increase spinal cord functionality even further. Unfortunately these drugs aren’t approved yet for humans use, and it will probably be a long while before they are. Of course, the stem cell research front continues to be a promising area for the future of paralysis treatments.

Rob Summers is just one of five million Americans who are living with some form of paralysis, and one of 1.3 million whose lower body is completely paralyzed due to spinal injury. Let’s enjoy the moment with him, and hope that this innovative treatment will allow many others to soon follow in his footsteps.

[image credit: GlobalNews]

image: Summers
video: Summers

Peter Murray was born in Boston in 1973. He earned a PhD in neuroscience at the University of Maryland, Baltimore studying gene expression in the neocortex. Following his dissertation work he spent three years as a post-doctoral fellow at the same university studying brain mechanisms of pain and motor control. He completed a collection of short stories in 2010 and has been writing for Singularity Hub since March 2011.