POSTED 22 FEBRUARY 2007
Panacea for paralysis?
About 10,000 Americans suffer severe spinal-cord injury each year, primarily due to car accidents. The higher the injury, the worse the paralysis. Injury to the neck can cause quadriplegia - inability to move the limbs.
Courtesy P. Hunter Peckham, Cleveland FES Center
Participants at the February meeting of the American Association for the Advancement of Science in San Francisco heard about two futuristic systems that could help quadriplegics move their muscles through electrical stimulation. One system "reads" the intention to move with an electrode placed on the brain. A second system takes its control signal from activation of those muscles that the patient can still control.
Even in severe quadriplegia, some muscle control remains, says P. Hunter Peckham of Case Western Reserve University. "All patients have something. Even if it's a very high level of injury, they still have some control over the muscles that pull the shoulders."
And that control can be used to regulate prosthetic devices.
Courtesy P. Hunter Peckham
The technology Peckham is helping develop at the Cleveland Functional Electrical Stimulation Center reads electrical contraction signals from muscles that can still be controlled, or from the position of joints that can be moved. The system then initiates movement by electrically stimulating muscles that the remaining nerves cannot reach. Each voluntary movement, Peckham says, represents a decision by the patient, who can learn to control hand muscles by moving, say, the wrist or shoulder. The research center is a consortium of the Louis Stokes Cleveland VAMC, Case Western Reserve University and MetroHealth Medical Center.
For these tiny electrical signals to control muscles, they must be processed in a control unit, and then delivered over a network of fine wires implanted under the skin. The signal is delivered either directly to the muscle, or to the motor nerve that normally controls the muscle. Because the control unit is outside the body, the system must communicate across the skin with electromagnetic radiation.
The rehabilitation process takes several months. After a thorough diagnosis, the target muscles, weak from non-use, are strengthened with several weeks of electrical stimulation. Then the surgeons install the wires, sensors and stimulators. Following a brief recovery period, the patient begins training to use the system.
Although every patient has a slightly different disability, the system can be tailored to the individual, Peckham says. "There is a standard device that we use that has two channels for recording [electric activity in the muscles], that can stimulate 12 muscles.".
To date, 11 patients have received experimental systems to control one or both arms, Peckham says, and are using them to perform "the activities of daily living, eating, writing, holding a pencil to type, grooming, brushing teeth, shaving, drinking, eating. What do you want to use your hands for? That's what dictates the objectives, and whether a person is a viable candidate. If they want to be a piano player, we don't have it as an objective to create fine individual finger control. We are trying to supply functional use to restore daily activities."
Courtesy P. Hunter Peckham
A test of slightly different technology, made by NDI Medical, will start within a year, says Peckham. And while most of the research (see #1 in the bibliography) has been done on patients with spinal cord injuries, Peckham expects the approach could be adapted to other disabilities, so long as the muscles and nearby motor nerves are intact. Candidate conditions include cerebral palsy, multiple sclerosis, and stroke.
Reading the brain
A second technological fix for paralysis does not need working muscles for a control signal -- and thus could treat the most extreme cases of paralysis. That includes the cruel "locked-in" syndrome, where patients "can think about moving, but cannot execute the movement," said John Donoghue, professor of neuroscience at Brown University.
Donoghue is involved in a technology called "Braingate" that literally "reads the mind" using electrodes implanted on the part of the brain that controls motor movement. The 100 hair-thin electrodes connect via cable to a processor outside the skull, which decodes the signals and turns them into movement commands that can be directed to control a computer, wheelchair or prosthetic device.
The first question about the technology was whether the brain was still up to the job, Donoghue said. "Does the motor cortex have neural activity more than a year after injury? Can this neural activity be changed by the patient?".
The system is being used in a clinical trial for people with spinal cord injury and other disabilities, and has been implanted for more than 1600 patient-days without harm (see #2 in the bibliography).
Four patients have received the implants, Donoghue said, and "The neurons are there, they can be activated by the patient, in all patients we have tested regardless of disorder. They could all move the cursor from point to point.".
Locked in no longer
Moving a cursor should allow a patient to use a computer, and while that's same-old, same-old to most of us, it's a different story if you are locked-in due to a stroke in the brain stem, or paralyzed due to spinal cord injury or a neurodegenerative disease such as ALS. Donoghue said the locked-in experimental subject, after getting the implant, typed "I love it!" on the screen.
This was her first verbal communication in nine years.
Courtesy John Donoghue, Cyberkinetics Neurotechnology Systems.
Beyond controlling a computer cursor, the BrainGate system could be paired with a functional electrical stimulation system that could restore partial arm and hand function to people with paralysis, allowing them to do basic tasks.
Eventually, Donoghue says, it should be possible to bypass several types of neurological damage and reconnect patients to the world. "We want to create a nervous system, and couple the brain back to the muscles. In five years, we want [quadriplegics] to be able to feed themselves.".
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Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive