Paralyzed rats with spinal cord injuries are now walking, running, and even climbing stairs on their way to chocolate rewards thanks to a combination of chemicals and electrical stimulation.

Screenshot by Elizabeth Armstrong Moore/CNET

While it remains unclear whether the development in rats will translate to humans, the ability of the rats to voluntarily initiate movement has led researcher Gregoire Courtine to get extremely animated as he describes a profound change in our understanding of the central nervous system.

"After a couple of weeks of neurorehabilitation with a combination of a robotic harness and electrical-chemical stimulation, our rats are not only voluntarily initiating a walking gait, but they are soon sprinting, climbing up stairs, and avoiding obstacles when stimulated," Courtine, whose findings appear in this week's Science, said in a news release.

Courtine, alongside researchers at the University of Zurich and the Swiss Federal Institute of Technology (EPFL), initially set out to study whether severely injured and paralyzed rats were able to achieve the neuroplasticity observed in more moderate cases.

He found that chemicals injected into the rats that bind to dopamine, adrenaline, and serotonin receptors on spinal neurons served as surrogate neurotransmitters typically released by brainstem pathways in healthy subjects to trigger and coordinate lower body movement.

Then, just 5 to 10 minutes after injecting the chemical cocktail, his team electrically stimulated the spinal cord via electrodes implanted in the epidural space. "All that is left [is] to initiate that movement," said contributing author Rubia van den Brand.

Courtine's team decided to place the rats in a mechanical harness that did not encourage movement but merely prevented the rats from losing balance, thereby giving them the impression of possessing a normally functioning spinal column. They then placed chocolate rewards on the far end of the platform.

After what they called "willpower-based training," the researchers observed a four-fold increase in nerve fibers throughout both the brain and the spine, and that these new fibers bypassed the original spinal lesion, creating a pathway for brain signals to reach what Courtine calls the "awakened" spine.

While it may not be obvious in the video below, the rats initiated movement toward the chocolate voluntarily, and it was their own hind legs, not the harness, that supported their weight as they moved.

"This is the world-cup of neurorehabilitation," Courtine said. "Our rats have become athletes when just weeks before they were completely paralyzed. I am talking about 100 percent recuperation of voluntary movement."

Courtine hopes to begin human trials within a year or two at Balgrist University Hospital Spinal Cord Injury Centre in Zurich. Meanwhile, researchers at EPFL are working via the NeuWalk project to design a spinal neuroprosthetic system similar to the one used in this study but for human implantation.