The electrodes stimulated the spinal cords of the patients while they engaged in specific motor tasks involving their paralyzed limbs. Before the patients were injured and their spinal cords were damaged, their brains would have sent those key electrical signals to their legs.
The new study upends the assumption that two years post-accident is a point of no return for people paralyzed due to a spinal cord injury. In the first months after a paralysis-inducing accident, patients might regain some function of their legs and lower torso with hard physical rehabilitation and the spontaneous regeneration of some nerves. But more than two years after these patients have been injured, those treating them have long thought there was little to be done.
The therapy reported Tuesday in the journal Brain proved promising as early as its first week of testing on four paraplegic subjects, each of whom was recruited to the study more than two years after his accident.
The trial's success suggests that "a large cohort of individuals, previously with little realistic hope of any meaningful recovery from spinal cord injury, may benefit from this intervention," said Dr. Roderic Pettigrew, director of the National Institute on Biomedical Imaging and Bioengineering, which supported the research.
The success of paraplegic patients in learning to flex previously immobilized ankles, toes and knees also suggests that even in those with severed spinal cords, voluntary movement may not require signals from the brain's motor command center.
With the impetus of a jolt of electricity and the patient filling in some sensory and perceptual information, the brain may enlist local motor circuits, or find a way through some usually dormant signaling path, to initiate movement, said UCLA researcher V. Reggie Edgerton, who co-wrote the report on the new methods.
At the heart of the new rehabilitative approach is a suite of electrodes that is surgically implanted to deliver a current of electric energy to the spinal cord -- just below the patient's injury -- as the patient tries, practices and refines voluntary movements. The spinal cord stimulator was first designed to relieve back pain.
Researchers still aren't sure whether it's practice that allows the growing accuracy, force and speed of voluntary movements, or whether that's the result of cumulatively more electrical stimulation. But it appears, said Edgerton, that the spinal cord stimulation "could be reawakening ... connections" severed by injury.
In the research team's first report, Edgerton and his colleagues in 2011 described the progress of then-25-year-old Rob Summers, completely paralyzed below the chest after a hit-and-run accident in 2006. While receiving spinal electric stimulation and being supported in a harness, Summers quickly trained his lower limbs to support his full weight for at least four minutes, and to make stepping motions upon command.
News of that preliminary victory was published in Lancet. But the team's replication of that feat in three more paralyzed patients -- including in two patients with a disruption of signals in both directions -- demonstrates that Summers' case "was not an anomaly," said Susan Howley, executive vice president for research at the Christopher and Dana Reeve Foundation, which provides patient advocacy and funds spinal cord injury research, and partially funded the current study.
"We can now envision a day when epidural stimulation might be part of a cocktail of therapies used to treat paralysis," Howley added.
The three other paraplegics -- Andrew Meas, Dustin Shillcox and Kent Stephenson -- all had been paralyzed for longer than two years.
Edgerton and his fellow investigators are exploring whether they can send electrical currents powerful enough to drive such learning through the skin, obviating the need to surgically implant the electrode arrays. And they are exploring whether similar technology and training can help quadriplegics recover some voluntary use of their upper limbs and bodies.
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