It’s a strange sight: a paralyzed rat walking on its hind legs in a precise cadence, all controlled by a computer.
“It is a little bit Frankenstein,” says Gregoire Courtine, a neuroscientist at the École Polytechnique Fédérale in Lausanne, Switzerland, who in a paper published yesterday in Science Translational Medicine describes his efforts to use electronics to restore fluid, realistic movements to paralyzed animals.
The study is part of a wider effort to help paralyzed people walk again by zapping their spinal cords with electrical pulses. These signals can replace commands normally sent out by the brain, but which are interrupted when the spinal cord is injured.
This spring, doctors and researchers from the University of Louisville and the University of California, Los Angeles, said four men who had been paralyzed for years were able to regain movement in their legs, hips, ankles, and toes, and even stand using an implanted device that stimulated their spinal cords, a technique called epidural stimulation.
Though the movements achieved were modest—and fall short of allowing the men to walk on their own—the technology let them exercise their legs, which seemed to restore some movement.
A limit to epidural stimulation so far is that the electrical pulses don’t produce complex, coӧrdinated movement. Also, in human tests, the stimulators are controlled manually. That’s where the system Courtine developed could come into play. By filming the rats as they walked, the Swiss team fed the images to software that quickly adjusted the pattern of stimulation to produce synchronized stepping movements.
Such a system could help a person walk rhythmically and maintain his balance. “The better it is, the better it will free up the individual that is being stimulated so that person does not have to make constant decisions,” says V. Reggie Edgerton, a physiologist at UCLA who has tested epidural stimulation on patients (see “Paralyzed Man Stands with Aid of Spinal Stimulation”).
To produce their results, the Swiss scientists severed the spinal cords of a half-dozen rats and then implanted flexible electrodes into the lower part of their spinal cords. The animals were also given a type of drug known as a serotonin agonist, which Courtine says readies the spinal cord to communicate with the legs, an ability that’s depleted after an injury. With their weight supported by a harness, the rats were placed on a treadmill or on a runway with obstacles.
“This is the first closed-loop control system that can really adjust leg movements in real time, despite paralysis,” Courtine says. Each of the rats walked at least a thousand successive steps and successfully navigated rodent-sized stairs.
His team hopes to test its ideas in a human volunteer next year. “The idea is to use this in the rehabilitation room,” Courtine says, citing evidence that exercising the spinal cord and legs may partly restore severed connections to the brain.
Epidural stimulation technology is still a long way from allowing paralyzed people to walk on their own, though. Hunter Peckham, a bioengineer at Case Western Reserve University, says that patients want to control their own movements, which means that future versions of these systems must strike a balance between automated routines and movements picked by the user.
Courtine says his group is working on developing a brain-machine interface, such as electrodes implanted in the motor cortex of the brain to record intended movements, that might eventually allow patients to control a spinal stimulator, and the movement of their legs, using their own thoughts.