For the first time ever, a man paralyzed from the chest down has walked unaided.
Baseball champion Rob Summers was hit by a speeding car three years ago, and was told he would never walk again. But, despite being unable to use his brain to control his limbs, Summers has regained the ability to stand and walk.
Researchers from the University of California, Los Angeles, the California Institute of Technology and the University of Louisville used an electrode array to stimulate the spinal cord's own neural network.
It appears that there's enough control circuitry in the lower spinal cord - below the level of Summers' injury - to control standing and stepping motions.
Through earlier research, the team had discovered that animals with spinal-cord injuries could stand and take coordinated steps while being stimulated epidurally — in the space above the dura, the outermost of the three membranes that cover the brain and spinal cord. However, it was unclear whether the same would apply to human beings.
But, says Joel Burdick, a professor of mechanical engineering and bioengineering at Caltech, high-density epidural spinal stimulation, which uses sheet-like arrays of numerous electrodes to stimulate neurons, can "stimulate the native standing and stepping control circuitry in the lower spinal cord so as to coordinate sensory-motor activity and partially replace the missing signals from above, and shout 'get going!' to the nerves."
Before being implanted with the array, Summers had hundreds of training sessions over more than two years, during which he was suspended in a harness over a moving treadmill while therapists manipulated his legs in a repetitive stepping motion. This had essentially no effect.
But after the device was implanted, Summers was able to push himself into a standing position and bear weight on his own. He can now remain standing, and bearing weight, for 20 minutes at a time. With the aid of a harness support and a little assistance, he can make repeated stepping motions on a treadmill, and can voluntarily move his toes, ankles, knees, and hips.
He has no voluntary control over his limbs when the stimulation is turned off.
Summers has also experienced improvements in several types of autonomic function, such as bladder and bowel control, as well as temperature regulation — a surprise outcome, Burdick says.
The scientists aren't yet fully sure how all this has been achieved.
"Somehow, stimulation by the electrodes may have reactivated connections that were dormant or stimulated the growth of new connections," says Burdick. It appears that the neural pathways below and perhaps also above the site of injury have been reorganized.
Notably, Summers had some sensation in his lower extremities after his injury, which means that the spinal cord was not completely severed; this may have affected the extent of his recovery.
The team plans to try the procedure again on five other patients. "While these results are obviously encouraging, we need to be cautious, and there is much work to be done," says V Reggie Edgerton of UCLA.