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 …