Video gif by Michelle Starr/CNET

We've seen exosuits that apply external force to allow the paralysed to move their own limbs -- but a solution that doesn't require a chunky, complicated wearable, but relies on internal stimulation, looks like it is on the way.

It has been tested and proven as part of a project called NEUWalk by researchers at the École polytechnique fédérale de Lausanne, Switzerland, using a rat with a severed spinal cord -- rendering its hind limbs completely paralysed.

The project operates on the notion that the human body requires electricity to function. The brain moves the body by sending electrical signals down the spinal cord and into the nervous system. When the spinal cord is severed, the signals can no longer reach that part of the spine, paralysing that part of the body. The higher the cut, the greater the paralysis.

But an electrical signal sent directly through the spinal cord below a cut via electrodes can take the place of the brain signal, as the team at EPFL, led by neuroscientist Grégoire Courtine, has discovered.

The team severed the spinal cords of several rats in the middle-back, completely paralysing the rats' lower limbs. They then implanted flexible electrodes into the spinal cord at the point where the spine was severed, allowing them to send electrical signals down to the severed portion of the spine.

This in itself, however, isn't enough to enable the rat's legs to move in a walking motion. The way the brain sends electrical signals isn't an indiscriminate stream -- instead, the frequency of the electrical stimulation controls how high the rat lifts its legs, for instance.

By carefully studying all aspects of how electrical stimulation affects a rat's leg movements -- such as its gait -- the team was able to figure out how to stimulate the rat's spine for a smooth, even gait, and even take into account obstacles such as stairs.

"We have complete control of the rat's hind legs," Courtine said. "The rat has no voluntary control of its limbs, but the severed spinal cord can be reactivated and stimulated to perform natural walking. We can control in real-time how the rat moves forward and how high it lifts its legs."

Clinical trials on humans may start as early as June 2015. The team plans to start testing on patients with incomplete spinal cord injuries using a research laboratory called the Gait Platform, housed in the University Hospital of Lausanne, Switzerland. It consists of a custom treadmill and overground support system, as well as 14 infrared cameras that read reflective markers on the patient's body and two video cameras for recording the patient's movement.

"Simple scientific discoveries about how the nervous system works can be exploited to develop more effective neuroprosthetic technologies," said co-author and neuroengineer Silvestro Micera. "We believe that this technology could one day significantly improve the quality of life of people confronted with neurological disorders."