Four individuals diagnosed as having complete paralysis of the legs were able to intentionally move their knees, ankles, and toes while undergoing electrical stimulation of the spinal cord, according to a study published yesterday in the journal Brain. The novel therapy has the potential to change the grim prognosis of people who have been paralyzed for years, say the researchers involved in the study based out of the University of Louisville in Kentucky.
The research is a continuation of a 2011 groundbreaking pilot trial that demonstrated that electrically stimulating the spinal cord in precise ways enabled a man paralyzed below his chest to stand independently for minutes at a time. The announcement of that pilot trial was incredibly exciting, but scientists wondered if it could be repeated with other individuals. The new paper reveals that the therapy has been successful in four people, and that it can enable not only independent standing, but also other kinds of voluntary leg and foot movement.
"When we first learned that a patient had regained voluntary control as a result of spinal stimulation, we were cautiously optimistic," said Roderic Pettigrew, director of the National Institute of Biomedical Imaging and Bioengineering at the National Institutes of Health (NIH), which supported the study. "Now that spinal stimulation has been successful in four out of four patients, there is evidence to suggest that a large cohort of individuals previously with little realistic hope of any meaningful recovery from spinal cord injury may benefit from this intervention."
Two of the four patients had motor and sensory complete paralysis, meaning communication between the brain and the legs in these individuals was completely cut off. But even for these two patients, voluntary movement was restored with the stimulation—a surprise to the researchers, who had assumed that at least some of this sensory pathway needed to be intact for the therapy to be effective.
The researchers say they can't identify the exact mechanisms that enabled these unexpected results. How the brain is communicating with the lower spinal circuitry when all ties were supposedly cut off is, for now, a mystery the researchers will have to investigate further. In fact, they suggest that the medical field "reconsider the mechanisms contributing to paralysis in humans."
The stimulation therapy involves implanting a 16-electrode array in the epidural space next to the outermost protective layer of the spinal cord. The array is connected to a pulse generator resembling a pacemaker that's implanted nearby. The pulse generator is controlled wirelessly by a programming device outside the body.
The array delivers electrical pulses to the spinal cord below the site of the injury, awakening the connections of that circuitry and getting it to function again. With the stimulation turned on, the four paralyzed men in the study were able to make voluntary leg, ankle, and toe movements on command. That's an astonishing achievement, considering that no one has reached that level of success in a human prior to this series of experiments.
The work is led by neuroscientists Susan Harkema and Claudia Angeli at University of Louisville's Frazier Rehab Institute. IEEE Spectrum featured Harkema's research last year with a focus on the fourth study participant, Dustin Shillcox, who at the time had just begun his stimulation therapy. The new study shows that he made excellent progress in the interim.