A C7-T1 paraplegic who had complete motor paralysis but incomplete sensory awareness is surprised that a groundbreaking experimental procedure enabled him to stand voluntarily more than three years post-injury.
On Dec. 7, 2009, a five-inch long array of 16 paired electrodes was implanted on the outer surface of Rob Summers’ lumbosacral spinal cord, the segment that receives and sends nerve impulses to the feet, ankles, knees and hips. The experiment began a little more than two weeks later. On the third day, with the epidural stimulator switched on, Summers leaned forward in his wheelchair and stood up without assistance. He remained standing a little over 4 minutes.
“I felt disbelief, shock, and amazement,” says Summers, 25, who was injured in July 2006. His unassisted standing time increased over the duration of the experiment, but is only possible with the stimulator switched on.
Susan Harkema, lead researcher in the joint effort by the University of Louisville, UCLA and the California Institute of Technology, also expressed surprise. “We weren’t expecting such robust behavioral changes so soon.” The findings, summarized in a May 19 news conference, were published in The Lancet. The study was funded by the Christopher and Dana Reeve Foundation and the National Institutes of Health.
Dr. Reggie Edgerton, who designed and supervised the experiment, explained that the stimulator, originally designed for pain relief, delivered “tonic, continuous stimulation” below the level of injury, enhancing “excitability” of the intact spinal cord, which enabled the receiving and sending of nerve impulses. Edgerton is well-known for his work in locomotor training — in which the subject, suspended from a harness, walks on a treadmill with assistance — a critical component of the experimental procedure.
Summers participated in 170 LT sessions over a 26-month period prior to stimulator implantation in order to pattern memory into the lumbosacral cord and build physical conditioning. “These neurons are smart,” said Edgerton in an interview with The Washington Post. “They can sense all the … information coming from the legs … [and] they know what to do next.” Paraplegics with incomplete motor injuries have previously made gains in functional walking ability with locomotor training, but Summers is the first para with a complete motor injury to be able to stand and step voluntarily. No detectable gains in motor ability were evident until the stimulator was turned on. Over time, Summers’ ability to voluntarily control muscle movement in his toes, ankles and legs improved.
Unlike functional electric stimulation, which drives peripheral nerves and muscles directly, an epidural stimulator activates the inherent intelligence of the spinal cord while the subject supplies the muscle power. Summers also noticed improved bladder control after seven months of stimulation. “About 80 percent of the time I can pee voluntarily. I can go if I want and hold it when I need to.” Prior to the experiment, “I had no control at all.” Summers noted improvements in bowel control, sensory awareness and sexual response as well.
While this experiment provides proof of concept for further research, Harkema pointed out that Summers is only one subject. Nevertheless, she says, “these results open up a whole new world of possibilities … We are currently studying application to quadriplegia in animals.”
For more information, visit www.christopherreeve.org.