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."
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