In a first step toward helping the paralyzed to walk, scientists have found brain areas that control movement continue to work normally in patients with spinal cord injuries that have left them immobile.
The promise is in technologies now under development that might serve as brain-computer interfaces, eventually enabling quadriplegics -- also known as tetraplegics -- to leave their wheelchairs, using signals from an implant in their brain, the investigators said in the British journal Nature. Any practical applications are years away, they cautioned.
The functional magnetic resonance imaging study of five patients who suffered nerve damage one to five years earlier revealed the brains of those unable to move below the neck respond in much the same way as do those of healthy individuals with no spinal injury.
The study by researchers at the University of Utah in Salt Lake City appears to calm concerns that the brain's motor centers will cease to function if they are not put to use and suggests computer implants to bypass damaged nerves might one day make it possible for paralyzed people to move and perhaps even walk again, scientists told United Press International.
"It won't happen next year, but it will happen," Jeffrey Goldberg of the Department of Neurobiology at Stanford University in Palo Alto, Calif., told UPI. "It may be that surface, rather than implanted sensors, may be refined sufficiently, however, avoiding the need for implants."
Researchers had feared the brains of the paralyzed might not retain the ability to send signals to muscles because when portions of the brain are not used, they often undergo "reorganization," under which other areas take over the computing power for other purposes. This does not appear to be the case for at least a while.
"The motor part of the brain does not significantly reorganize for at least five years after spinal cord injury. That's what we showed," lead study author Richard Normann, professor of bioengineering and ophthalmology, said in a telephone interview. "This is very encouraging news."
While the experiment cannot rule out changes occurring in the brain's motor cortex at a finer scale beyond the MRI resolution, "these finding are somewhat reassuring for those who think about neuroprostheses," said physiologist Ferdinando Mussa-Ivaldi of the Department of Physical Medicine and Rehabilitation at Northwestern University Medical School in Evanston, Ill.
"At least one may have some confidence about what regions should be considered for capturing, say, hand movement commands," he told UPI.
"This study suggests that many years from now, technologies being developed in the laboratory today might enable paralyzed individuals to stand up out of a wheelchair and walk," Normann said.
Already, he noted, "a number of researchers are trying to develop brain-computer interfaces that can be used to control external devices -- robotic arms, wheelchairs, computer terminals -- using signals originating within a paralyzed person's brain."
Initially, command signals from the brain could be used to control such devices, said Normann, who is also using the "engineered" approach in designing artificial systems to help the blind to see and the deaf to hear.
"But eventually these same signals perhaps could be used to directly control the muscles of a paraplegic person, ultimately allowing them to move their body just through the desire to do so," he said. "That's really a long way away."
The study is but a first step. The MRI images showed the appropriate brain areas of five young adults paralyzed in traffic accidents "lit up" when the subjects were asked to move their hands or ankles, purse their lips, rotate their elbows and extend their knees. The same reaction came from the brains of fully mobile students in response to the same requests.
The lip pursing came easily to all five volunteers with nerve injuries since the head rises above the damaged section of the spine. One of the subjects was able to move his hands, the other four were quadriplegics, incapable of any movement below the neck.
The brain response implies the motor cortex does not degenerate significantly -- and can still send command signals -- in people paralyzed by spinal cord injury.
Much work remains, Normann said, including:
--lab experiments to determine the safety of long-term implantation of an electrode to read brain signals;
--once deemed safe, human tests of implants, perhaps in patients undergoing brain tumor surgery;
--trials with paraplegics and quadriplegics to determine whether the electrodes could receive command signals from the motor cortex;
--eventually, implantation of electrodes adjacent to the spinal cord to receive command signals from the electrodes in the brain -- via wires or radio signals -- and relay them to the appropriate muscles.
Animal tests have already indicated small electrodes implanted in the sciatic nerves receive external command signals and can be used to control ankle movements.
"The idea of computer implants is conceptually straightforward," W. Zev Rymer, research director of the Rehabilitation Institute of Chicago, told UPI. "However, I doubt that it is yet practical from a medical standpoint."
While some of the technologies already exist, important challenges remain, added Ivaldi.
"One is to establish long lasting and widespread connections between brains and conductive materials. The currently used glass and metal electrodes are not likely to offer the best solutions," he told UPI.
"Another challenge concerns our ability to act on the mechanisms that are responsible for the reorganization of brain circuitry. In other words, we should find ways to 'program' the nervous tissue so that a patient may learn to control an artificial arm even if the electrical contacts are not placed exactly where the commands for the arm were originally formed."
The work is "just the beginning of this new therapeutic approach to problems of the nervous system," said Normann, who envisions a tetraplegic eventually controlling his wheelchair -- or his bladder -- through volitional thought.
Restoring movement will require a two-way approach. Bypassing the damaged spinal cord, brain signals will have to be sent through electrodes to the muscles, which will then have to provide sensory feedback to the brain. The brain, in turn, must "know" the physical location of, say, the legs, to exert control over their movement. This may require additional electrodes in the sensory cortex and outside the spinal cord to carry the message from the muscle to the brain, scientists said.
This "engineered" approach comprises one of two major fronts currently pursued in paralysis research. The other involves biological solutions using gene therapy or stem cells to regenerate damaged spinal tissue.
"Certainly there is room for both to work together," Goldberg told UPI. "The bio-robotic interface is already being looked at in humans, whereas the genetic/molecular/stem cell approach is still mostly confined to animal models for further study first."
While the work opens the door to new devices, it is important to avoid raising false hopes, Normann cautioned.
"It's important we not oversell what we're trying to do," he said." It's a long race we're running, and we need to jump many more hurdles. But we're running as fast as possible and jumping as high as we can."