It is the stuff of nightmares: trapped in an immobilized body, unable to move a finger or bat an eyelid, yet with sight and hearing and thought undiminished. The impulse to whisper, "I love you," or to scream, "I am in pain," is smothered by one's own unresponsive muscles. To the outside world, you are all but dead. Inside, you burn with life.
Neurologists call patients who are totally paralyzed "locked-in," and diagnoses of Lou Gehrig's disease or a brain-stem stroke are among the most feared of all neurological disorders. Doctors often counsel patients and their loved ones to opt against life support before becoming fully locked-in, because such a life is thought to be unbearable.
But a German neuroscientist has found a way to give voice to 11 patients around the world with a device that converts mental activity into computer commands. His experience has led him to challenge the prevailing medical assumption that locked-in lives are not worth living.
Niels Birbaumer, Ph.D., of the University of Tübingen calls his machine a Thought Translation Device, or TTD. It is attuned to a low-frequency brain wave called the slow cortical potential, which people can produce at will. By controlling their thoughts, patients can answer yes-or-no questions, spell out sentences or even surf the Internet.
More than 25,000 people in the U.S. live in severe or total paralysis. An accident or a catastrophic stroke paralyzes some instantly. Others bear the slow agony of amyotrophic lateral sclerosis, or ALS—commonly known as Lou Gehrig's disease. In such cases the nerves commanding the voluntary muscles slowly degenerate. Astrophysicist Stephen Hawking, who suffers from ALS, retains control of a few muscles in one finger; with these, he operates a computer that generates his world-famous voice. For some, though, even that amount of control is gone.
That's the case for Hans-Peter Salzmann, a former lawyer with ALS living in Germany. Salzmann commands one muscle just below his left eye. With a caregiver slowly reciting the alphabet, Salzmann can draft messages by signaling "yes" to the appropriate letter. But no truly private communications can be written with someone sitting inches away, waiting for a face to twitch.
Since 1996, however, Salzmann has been able to compose messages on his own by using the TTD that Birbaumer and his colleagues built. This in itself is a first: No one before had communicated via brain waves in a real-world environment.
The device scans Salzmann's brain waves through electrodes pasted to his scalp. By consciously changing his thought patterns, Salzmann can signal the TTD. First, he builds mental tension by imagining a stoplight changing from green to red. Then, if he sees a desired letter among a group at the top of a computer screen, he envisions the light changing back to green. Repeating the process, he whittles the group to a single character and then builds a string of characters into a message.
"I first heard about Birbaumer's device at an international meeting on ALS in 1998," says Mary Lyon of the ALS Association located in Calabasas Hills, California. "The audience was stunned." The TTD has in many ways brought a degree of independence rarely found in people with profound paralysis. Salzmann's system now features a built-in Internet browser so he can read online newspapers and books. In fact, the device has password protection to help insure his privacy—a huge concern for many locked-in patients. Birbaumer contends that by and large, doctors and caregivers have a poor understanding of the experiences of locked-in patients. While admittedly devastating, the condition—as reported by those who suffer from it—does not appear to be as intolerable as commonly assumed.
In a study conducted by Birbaumer's colleagues at Tübingen, ALS patients with severe paralysis were surveyed on their quality of life, looking for signs of depression. Although ALS patients were more depressed than the general population, those surveyed were not nearly as distressed as people suffering from clinical depression.
"The widespread belief that their quality of life is very low, and that they therefore have to die, is a prejudice," says Birbaumer, who adds that some 95 percent of patients who become locked in refuse artificial respiration on the advice of their doctors. "These patients are killed because of that prejudice."
Niels Birbaumer was born to German parents in Czechoslovakia three days after the end of World War II, and came of age in Austria during the tumultuous 1960s. He was already a full professor by the age of 30; and in addition to his position at Tübingen, where he is director of the Institute of Medical Psychology and Behavioral Neurobiology, he is on the faculty of universities in Italy and the U.S.
Birbaumer has consistently probed the far reaches of mental activity, trying to understand how the brain copes with extraordinary circumstances. An early project examined how people who are born blind process information. Later, he looked for ways to treat the so-called phantom limb pain that often torments amputees.
By the early 1990s, Birbaumer was working with epileptics, trying to stave off impending seizures. He and his colleagues discovered that controlling the slow cortical potential, or SCP, can derail an epileptic seizure before it grips the sufferer.
A slow cortical potential is a type of electrical activity in the cortex, the outer part of the brain. Electroencephalograms (EEGs) detect this activity through electrodes on the scalp. These electrodes measure the voltage difference, or potential, between two points in the brain.
Anything the brain does, from adding a row of numbers to directing your arm to swat a fly, creates a voltage that an EEG can pick up. SCPs are produced when the brain is engaged in a spectrum of mental activities. Thoughts pertaining to anticipation—waiting in a runner's crouch, for example—create a negative potential. While those involving release, such as beginning to sprint, create a positive one. And unlike most brain waves that flit across the EEG monitor in milliseconds, SCPs build up over several seconds. This relatively slow speed makes them the easiest brain waves to detect and influence.
Birbaumer's team taught a group of epileptics how to change the nature of their SCP; if they could do this when they felt a seizure coming on, they might be able to avoid it entirely. The results were phenomenal. Without drugs or surgery, more than half the patients in the study significantly curbed their number of seizures. Some were able to eliminate seizures altogether. For this, Birbaumer was awarded the Leibniz Prize, the German equivalent to the Nobel Prize in medicine, in 1995.
The prize carried a cash grant of some $1.5 million, allowing Birbaumer to devote his research to developing communication for locked-in patients, a project that might never have attracted conventional funding because the prospect of immediate results seemed remote. "With the award, we could work for five years without publishing," says Birbaumer.
Building a communications device for a person with severe paralysis meant tapping directly into mental function. Birbaumer realized he already had a working model for such an unorthodox intervention. To fend off a seizure, epileptics could change their SCP wave by force of will—imagining a tension being released such as a pistol cocked and then fired.
Banking on this, Birbaumer taught Salzmann and 10 other patients with near-complete paralysis to control their SCP. He then adapted an EEG machine to use the SCP state as a kind of computer cursor. With this, patients can winnow the alphabet to a single letter just as children can discover a particular animal, vegetable or mineral through playing a game of 20 questions. With the SCP, "he's identified a signal that he can get reliably from patients," confirms Charles Anderson, a Colorado State University computer scientist involved in developing brain-computer interfaces like the TTD. "That's not easy to do."
Similar devices exist in laboratories around the world, but few have been used by the locked-in. "Unlike many researchers, Birbaumer is working with real patients," says Jessica Bayliss, a researcher at Rochester Institute of Technology in New York who also works with brain-computer interfaces. In August of 2002, Birbaumer spent several weeks in Lima, Peru, training a fully locked-in businessman to communicate with the TTD. Although the patient can't do much more than answer yes or no questions, Birbaumer's training represents a breakthrough: No fully locked-in patient has made as much progress.
Birbaumer's device is a coup, but it is also achingly slow: 100 characters can take the better part of an hour (Salzmann spells faster using his twitching eye muscle). Researchers are investigating whether other brain waves might provide a clearer signal of intent to speed up communication. Birbaumer uses SCPs because "after 20 years of research, we know the physiological meaning of that wave." While these waves are, with practice, easily produced and controlled, they are too slow to tap out an instant message or direct a cursor on a computer screen.
Birbaumer believes the future of brain-computer interfaces lies in implanting electrodes directly into the brain. American neuroscientists have experimented with animals to create such direct connections for some time; researchers at Emory University in Atlanta have even implanted electrodes into the brains of terminally ill patients, with modest success. But there's a catch. "Our patients refused to have implants," says Birbaumer. "They are sitting there with artificial respiration, and someone offers to drill a hole in their heads and implant electrodes. They tell us they would rather do it slowly than take on all the risks from surgery. These patients don't have the time pressure to communicate that we do. They have totally different aspirations."
Birbaumer continues to give his patients what they do want. One man yearns to play chess online, so Birbaumer (in collaboration with Bayliss and others) is designing a special program to enable this. Another patient who enjoys pornography can now direct his computer to show him nude photos. But most are happy simply to compose a letter, to tell their children that they are loved.
"Humans are enormously adaptable," Birbaumer says, "and even in these extreme states, as long as they can communicate, their quality of life can remain high."