Even after he lost the use of his limbs, Christopher Reeve believed in keeping fit. All the scientists working on cures to paralysis had warned him “it won't do you any good if you don't keep your body in shape,” he said. The millions who now suffer (about 1 in 50 Americans has some paralysis, according to the Christopher and Dana Reeve Foundation) would do well to heed his advice—for they are closer to being able to walk again.
Gregoire Courtine and his colleagues at the Swiss Federal Institute of Technology have been working on ways to coax limbs paralyzed by spinal cord injury to move again. So far, their work has only been in rats, but they have seen much progress. In 2012, the researchers came upon a promising approach that combined chemical and electrical neuron stimulation, which they described in a paper in Science: Rats with damaged spines could use their legs anew. Now Courtine’s team has established how to control that motion automatically, even in rats with severe spinal cord injuries. Their most recent findings are published in the current issue of Science Translational Medicine.
In their earlier work, the scientists paralyzed their lab rats’ hind legs by cutting their spines without completely severing them, which is common in real spinal cord injuries. Some signals from the brain can still get through what attached nerves remain, but they are not strong enough to cause movement. Using pulses of electrical stimulation, chemicals to mimic neurotransmitters from the brain, and food placed in front of a rat’s nose, Courtine and his co-authors were eventually able to train dozens of paralyzed rats not just to move their hind legs, but to walk and to dodge obstacles. Upon dissecting the rats afterward, the team found that new nerve fibers had grown in the injured areas, restoring some of the spinal cord.
Though their original experiment showed incredible recovery in the rats they had injured, it could not tell the researchers how to adjust electrical frequencies and amplitudes to change an animal’s gait (which is needed to walk over different terrains and elevations). They have figured this out in their latest study, and they can now show what electrical stimulation frequencies and intensities produce a step of a specific height. Using this knowledge, they built an electric stimulator that modulated its signal. They then placed rats—this time with completely cut spines, representing the worse possible (and extremely rare) injury—in a harness that moved them forward through an obstacle course with stairs of various heights. By automatically changing the electrical signals according to the researchers’ calculations, they successfully altered how high a rat raised its leg in order to climb a stair.
With this breakthrough, the scientists hope to replicate their therapy in humans. That would benefit those with all kinds of paralysis, from mild to severe. Current therapies help some to regain a bit of motion, but the results are limited. Those with the worst injuries have almost no chance. Courtine’s team may have found a way to take a real step forward. They plan to begin trials next year. Superman would have been proud.