A promising new study shows that the nervous system can rewire itself—with a little help from neural engineers.
For someone with a spinal cord injury, destroyed neurons act like a roadblock that prevents movement commands from traveling down the spinal cord and along the nerves. Although an injured person wills his fingers to grasp a cup, for example, the command never makes it to his hand.
But a study published today suggests that precisely controlled electrical stimulation can encourage the nervous system to create detours around that roadblock, allowing the command to get through.
Neuroscientist Steve Perlmutter and his colleagues at the University of Washington devised a clever experiment using rats. The animals were first trained to perform a task in which they reached through narrow slots with their dominant forelimbs to grab food pellets. The rats were then given incomplete spinal cord injuries that almost totally paralyzed those limbs.
Next the rats were divided into three groups and, as if they were in physical therapy, trained again on the same task. The control group tried to perform the reach-and-grasp task unaided, the second group received random pulses of electrical stimulation in their spinal cords during the task, and the third group received stimulation pulses that were triggered by the rats’ attempts to move their immobilized limbs.
The key advance here is that triggering technique. The researchers used a device called the neurochip-2, which recorded the weak electrical signal from the limb muscles and used that signal as the cue to initiate a pulse of electrical stimulation in the spinal cord. When the attempted muscle movement was synchronized with neural stimulation, the researchers believe that surviving neurons in the spinal cord formed new connections linking the muscles to the brain’s motor control region.
What’s the underlying mechanism behind this remarkable repair work? I have just one word for you: neuroplasticity. Neural networks are malleable, and changing the patterns of connections between neurons can restore lost function. That’s why people who’ve suffered spinal cord injuries do rehab: They’re not trying to bring dead neurons back to life, but rather to teach the nervous system to work around them. However, people typically don’t recover much function with rehab alone.
Perlmutter’s research suggests that adding electrical stimulation to rehab could provide a real boost. Over the course of the three-month study, the rats with neurochips showed dramatic improvement. The synchronized-stimulation rats ultimately performed the task 63 percent as well as they had before their injuries. Both the control group and the random-stimulation group performed about 30 percent as well as they did pre-injury.
Spectrum has covered “closed-loop” neurostimulation systems before, most notably in this feature article written by researchers from the companies Medronic, Cyberonics, and Neuropace. The authors described systems that used various bodily signals to trigger electrical pulses that countered epilepsy attacks and chronic pain. Such smart and responsive systems, which are now being used in humans, seem a clear step forward in electrical therapeutics.
While the study from Perlmutter and his colleagues was conducted in rats, it points the way toward a new rehab strategy for people with spinal cord injuries. What’s more, it serves as a proof of principle for a strategy that may help people with other nervous system dysfunctions. By leveraging “the nervous system’s intrinsic capacity for reorganization and repair,” the authors write, electrical stimulation could help people regain lost motor abilities, perhaps, or bladder, bowel, or sexual function.