Silent Minds.(comatose patients)

Ten years ago, Adrian Owen, a young British neuroscientist, was working at a brain-imaging center at Addenbrooke's Hospital, at the University of Cambridge. He had recently returned from the Montreal Neurological Institute, where he used advanced scanning technology to map areas of the brain, including those involved in recognizing human faces, and he was eager to continue his research. The imaging center was next to the hospital's neurological intensive-care unit, and Owen heard about a patient there named Kate Bainbridge, a twenty-six-year-old schoolteacher who had become comatose after a flulike illness, and was eventually diagnosed as being in what neurologists call a vegetative state. Owen decided to scan Bainbridge's brain. "We were looking for interesting patients to study," he told me. "She was the first vegetative patient I came across."

For four months, Bainbridge had not spoken or responded to her family or her doctors, although her eyes were often open and roving. (A person in a coma appears to be asleep and is unaware of even painful stimulation; a person in a vegetative state has periods of wakefulness but shows no awareness of her environment and does not make purposeful movements.) Owen placed Bainbridge in a PET scanner, a machine that records changes in metabolism and blood flow in the brain, and, on a screen in front of her, projected photographs of faces belonging to members of her family, as well as digitally distorted images, in which the faces were unrecognizable. Whenever pictures of Bainbridge's family flashed on the screen, an area of her brain called the fusiform gyrus, which neuroscientists had identified as playing a central role in face recognition, lit up on the scan. "We were stunned," Owen told me. "The fusiform-gyrus activation in her brain was not simply similar to normal; it was exactly the same as normal volunteers'."

Excited by this result, Owen resolved to try to conduct brain scans of other vegetative patients in the Cambridge area. Since 1997, he has studied several dozen people, though he decided to use speech sounds rather than photographs to stimulate their brains. (Owen was concerned that showing images of faces might not be a reliable way to test recognition, since the eyes of vegetative patients often wander. "We shifted to auditory responses because you can always put a pair of headphones on the person and know that you are transmitting sound," he said.) Three years ago, he began using a functional MRI (fMRI) scanner, which is faster than a PET scanner, capturing changes in blood flow in the brain almost as they occur. The patients' brains were scanned while they listened to a recording of simple sentences interspersed with meaningless "noise sounds." The scans of some of the patients showed the same response to the sentences as scans of healthy volunteers, but Owen wasn't sure that the patients had understood the words. "So we went the next step up the cognitive ladder, to look at comprehension," he said.

Psycholinguists have shown that when we hear a noun at the beginning of a sentence we tend to associate the word with its most common meaning. For example, Owen said, most people hearing a sentence that begins, "The shell was . . ." think of an object typically found at the beach. But if the sentence is completed by the phrase "fired at the tank," the listener quickly corrects himself, a process that is evident on a brain scan. "You can actually see it happening and image it on the scanner," Owen said. "The beautiful thing about the psychological task is that we just do it automatically. When you play ambiguous sentences, areas in the inferior frontal lobe and in the posterior temporal lobe become activated, and these areas are very important for speech comprehension. They show that you understand the meaning of the word: it's not just about perceiving speech; it's about decoding. Your brain somehow appreciates that there are two meanings to a word like 'shell.' "

Owen eventually identified two vegetative patients whose brains showed the same activity in response to ambiguous sentences as the brains of healthy volunteers. He also took brain scans of healthy physicians, who were presented with the ambiguous sentences while under general anesthesia. Owen found that, as the effects of the anesthesia increased, the physicians showed less activity in the brain regions associated with comprehension. "That, of course, is in keeping with our personal experience of consciousness, which is that as you sort of drift into sleep you understand less and less of what is around you," he ...