Brain-wave Test Challenges Vegetative-State Diagnosis
Tests using an EEG have shown unexpected cortical functioning in vegetative patients
PHOTO: Peter Arnold/Alamy
6 August 2008— Eluana Englaro has been lying motionless in a hospital bed in Italy for 16 years. In 1992, Englaro survived a serious car crash that left her brain damaged, completely unresponsive, and unable to eat, drink, or breathe on her own. She is now in a class of patients diagnosed as ”persistently vegetative.” Her father, convinced that Eluana would have opposed the medical intervention she received, has fought in court for the past nine years for the right to remove her feeding tubes and turn off her respirator. In early July, he finally won, but Italian state prosecutors have 60 days to appeal.
End-of-life decisions in nonresponsive patients like Englaro and American Terri Schiavo pose a deep challenge to the science of consciousness. When these types of cases go to trial, courts spend much of their time hearing opinions on whether the patient is truly in a vegetative state and whether he or she has any chance of improving. The controversy surrounding these disputes is due in part to the primitive methods we rely on when assessing consciousness. But some scientists are working on technical ways to measure consciousness in patients with brain injuries.
Niels Birbaumer, a neurobiologist at the University of Tübingen, in Germany, used EEG recordings to study the brain activity of patients diagnosed as vegetative and found unexpected levels of cortical activity. He presented his work this month at the Euroscience Open Forum, in Barcelona, and discussed the medical implications.
In one of the studies, Birbaumer and his colleagues looked for patterns in the brain’s electrical activity as patients listened to sentences being read aloud. The experimenters attached 10 to 20 electrodes to the scalps of 98 patients who had suffered severe brain damage. The group was composed of both completely vegetative patients and others that still retained control of their gaze or other simple physical abilities. In the experiment, patients listened to a series of seven-word sentences. Half the time the sentences were semantically logical. The other half of the sentences ended with a nonsensical word. An example might be ”I baked a cake in the banjo.”
As the patients listened to the words, the researchers listened to the electrical activity in their brains. With EEG data from 100 trials, the researchers pieced together a signature response, called an event-related potential (ERP), for each patient who gave some indication of how he processed the errors he was hearing. When graphed out, an ERP is a collection of waves and spikes that chart the firing of neurons during the milliseconds following an event, such as hearing an unexpected word at the end of a sentence. Neuroscientists have studied and named the various components of the ERP and are beginning to understand what they mean in terms of how we think.
In this particular example, Birbaumer’s group was looking for a dip in the wave 400 milliseconds after a patient heard an incorrect sentence. The dip is called the N400, and many neuroscientists regard it as the cortical signature for processing semantic errors.
What the group found challenges the diagnoses of many of the patients they tested. Of the 38 participants considered persistently vegetative, 22 percent responded to semantic errors with an N400wave effect. The group found similar results when testing the ability to discriminate between tones of different pitches. The data suggest that these patients are capable of a higher level of processing than previously thought. Although they cannot interact with their environment, many people with severe brain injuries may still be responding to it internally.
On the other hand, says Birbaumer, the test can also provide more support that those patients who show no response with an EEG are truly in a vegetative state. It takes many EEG trials to sketch out an accurate ERP for each patient, but if it’s done properly, it could be convincing to both families and courts. ”I think [these tests] can help, but you have to do them many times,” says Birbaumer. ”If they fail to show anything repetitively, end-of-life decisions should be easier.”
About the Author
Morgen E. Peck is a freelance writer and former neuroscience researcher. In April 2008 she wrote about an EEG-based technique to speed the sorting of images.