One of the most amazing characteristics of the brain is its plasticity. After even some severe traumas, like having a hemisphere removed, the brain can adapt and move functions around to continue functioning. In the past it has appeared that only the brain was plastic because the spinal cord would not adapt in a similar way to injuries. Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL) have changed that though and given rats with severe paralysis the ability to walk again.
The first step of the experiment was to 'wake up' the dormant part of the spinal cord found beneath the injury. This was accomplished with a special chemical solution that replaced neurotransmitters normally released by the brainstem in order to stimulate dormant neurons. Next the researchers used electrodes to stimulate the spinal cord further, making it ready to operate.
The brain is not the only controller in the nervous system. Other networks of neurons, including the spinal cord, are able to respond to external stimuli, which is what causes involuntary motions. The researchers placed the rats on a treadmill and discovered it could walk. The spinal cord was taking in the information of the treadmill moving beneath it, and responded by having the legs move. This involuntary action was truly great to see, but the researchers, inspired by this success, decided to go a step further.
A new rig was created for the rats to use, but instead of a treadmill, the rats were gently suspended, to put all of their weight on their hind legs. With a chocolate treat at the end of the rig, the rats wanted to move forward; to voluntarily walk with their previously paralyzed legs. The rats got their chocolate, even when it required that they walk up steps.
The spinal cord, after being reactivated by the chemicals and electricity, grew new connections around the lesion that originally caused paralysis. The connection between the legs and the brain may not have been as strong as it would have been without the lesion, but it was enough for the rats to walk. It may be some time before we see humans benefiting from a similar treatment, but now we know complete recuperation of voluntary movement is possible.