Swiss researchers have enabled rats with severe spinal cord injuries to walk and swim by electrically stimulating a group of neurons located deep in the brain. The discovery may give researchers a new approach to treating severe spinal cord injury. The research, led by Lukas Bachmann at the Brain Research Institute at the University of Zurich, was published today in Science Translational Medicine.
In most spinal cord injuries, some nerve fibers connecting the brain to the spinal cord below the injury site remain intact, even in severe cases in which a person is paralyzed. Bachmann and his colleagues found that by stimulating a key region of the midbrain called the mesencephalic locomotor region, or MLR, the remaining intact nerve fibers could be recruited to improve walking and swimming movements in spinal-cord injured rats.
The scientists used a technique called deep brain stimulation. Electrodes implanted in the rats' midbrains sent 50 hertz cathodal pulses into their MLR regions. The extent to which the stimulation improved the rats' gait varied depending on the severity of the spinal cord injury. Rats who had lost 70 to 80 percent of their reticulospinal fibers were severely impaired, but not paralyzed—comparable to a human who can walk but has major deficits in strength and speed. Deep brain stimulation gave these rats a close-to-normal gait.
Rats that had lost more than 90 percent of their fibers were almost fully paralyzed in the hindlimbs—comparable to a human who is wheelchair-bound. Deep brain stimulation enabled these rats to move their hindlimbs while swimming.
It has been known for decades that the MLR orchestrates the parts of the brainstem that control walking. Recently scientists have used deep brain stimulation of this region to treat patients suffering from disorders such as Parkinson's disease. The new Swiss research suggests that this type of stimulation may also help people with spinal cord injuries. "I believe we have delivered the first promising indications that may help us in finding possible treatments for spinal cord injury," says Bachmann. "But much still remains to be investigated."
Bachmann says his research also provides the first indications of which parts of the brainstem may be responsible for conveying different components of walking during deep brain stimulation. "We think that areas closer to the midline in the brainstem do convey the rhythmic components of walking whereas areas more on the side convey the strength aspects of the MLR stimulation effect," Bachmann says.
Scientists have been experimenting with electrical stimulation of other parts of the central nervous system for many years in both animals and humans. In one recent and promising approach, researchers at the University of Louisville used epidural stimulation to enable a paralyzed man to stand on his own. The researchers used a 16-electrode array to stimulate the man's spinal cord below the site of his injury, essentially cutting the brain out of the equation. For more on that story, stay tuned for a feature we will post tomorrow.