Strokes and accidents that damage the brain or spinal cord sometimes leave people fully conscious but unable to speak or move. Trapped in their own bodies, the people who suffer from what is sometimes called locked-in syndrome are lucky if they can communicate their needs with a blink or a raised eyebrow. That may soon change. A team of neurologists has developed a device that allows paralyzed people to communicate through a computer without having to move a muscle.
Philip Kennedy, a neurologist in private practice near Atlanta, has been working on the implant--a millimeter-long electrode--for 12 years. Implanted into the part of the brain that normally controls the hands, the electrode, coated with growth factors that spur brain tissue to grow into it, picks up electric signals sent back and forth by nerve cells.
When a patient thinks about moving his hands, electrical activity near the electrode increases. Through an amplifier and antennas positioned underneath the scalp, those signals are transmitted to a computer, which uses them to drive a cursor across a screen. By concentrating or relaxing, a patient can control the firing of his neurons and make the cursor stop on an icon with a prepared message or on a letter of a keyboard display. The computer then speaks or prints a letter or message.
Kennedy and his partner Roy Bakay, a neurosurgeon at Emory University have tried the implant in two patients so far. The first, a woman suffering from amyotrophic lateral sclerosis, or Lou Gehrig's disease, passed away due to her illness 76 days after receiving the implant. Their second patient, a man paralyzed from the top of the neck down after a stroke, has had his implant for nearly a year. He hasn't quite mastered the keyboard, but he can position the icon near prepared messages. "He's delighted," says Kennedy, "and when it works for him he has a big smile on his face."
Kennedy and Bakay hope their implant will help people control prosthetic devices as well as computer cursors. There are approximately 5 million people in the world who are quadriplegic, paraplegic, or have locked-in syndrome. With enough funding, says Kennedy, he could help these people in as little as three to five years.
For tens of thousands of people suffering from paralysis or neurodegenerative disease, a direct connection to a computer could soon restore speech and even mobility. Neurologist Leigh Hochberg of the VA Medical Center in Providence, Rhode Island, is leading the second clinical trial of a brain-computer link called BrainGate. The system uses a sensor implanted into the motor cortex. Previous studies have shown that BrainGate can allow paralyzed people to perform simple tasks such as moving a computer cursor. The current trial will evaluate its safety outside the lab. Two people are already testing BrainGate at home, using the device to manipulate objects on a computer, and Hochberg hopes to recruit 13 more participants.
Although implants can be placed right next to the relevant neurons in the brain, they have drawbacks. Implants can inflame the surrounding tissue, and scarring can disrupt the connection between neurons and electrodes. A sensor developed by University of Pennsylvania neurologist Brian Litt could address those problems. It consists of electrodes embedded in a flexible plastic mesh that molds to the brain’s surface (but it does not penetrate the gray matter). Litt and his colleagues were able to record neural signals from cats’ brains for a few weeks without causing inflammation. Neuroscientist Gerwin Schalk of the New York State Department of Health has found that test sensors placed on the outside of human brains pick up signals that can identify spoken or imagined words. “The surface is a sweet spot,” he says.