In a startling new report in today's issue of the journal Science, however, scientists describe how the young accident victim in a vegetative state shows brain activity consistent with conscious awareness.
When the scientists spoke to her, advanced imaging showed, her brain registered activity in regions responsible for decoding language, just as the brains of normal volunteers do. When they used sentences with homonyms, which require more complicated semantic processing, the appropriate parts of her brain lit up, again just like healthy brains.
Either response might be dismissed as automatic and therefore unconscious. After all, some people in a vegetative state retain "islands" of preserved neural function, Nicholas Schiff of New York-Presbyterian Hospital/Weill Cornell Medical Center and colleagues found in a 2002 study, but not in areas involved in higher mental function. Similarly, studies have shown that some people who are asleep, under general anesthesia or in a vegetative state show brain activity consistent with perceiving speech and responding to emotion-laden words and their name.
That's why simply responding to speech, admits neuroscientist Adrian Owens of the Medical Research Council Cognition and Brain Sciences Unit, Cambridge, who led the new study, is "not unequivocal evidence that [the woman] is consciously aware."
So they asked her to imagine playing tennis. Remarkably, this made neurons fire in the premotor cortex, a region that hums with activity when you mentally practice sophisticated movement, from a jump shot to a backhand. Then they asked her to imagine walking through each room of her house. This time her parahippocampal gyrus, which generates spatial maps, became active, again just as in healthy volunteers.
"We know from extensive research that brain responses of this type do not occur automatically," says Prof. Owens, but "require the willed, intentional action of the participant."
He cautions that the results apply only to this patient, and that others in a vegetative state aren't this responsive. Indeed, 60 previous patients in a vegetative state show no such brain activity, says Steven Laureys of the University of Liege, Belgium. "But she was different," he says. "Her brain activity shows a clear act of intention. The activity in her higher-order cognitive areas means, to me, that she was consciously aware of herself and her surroundings."
Lionel Naccache of the National Institute of Health and Medical Research in Orsay, France, calls the woman's response to the tennis and home tasks "quite spectacular" and evidence of "a rich mental life." But he notes that consciousness, according to neuroscience, requires engaging "in intentional actions or interactions" with the outside world. If she is conscious, why does she show no spontaneous intentional behavior, especially since there is no damage to parts of the brain that control moving or speaking?
Although the woman fits the diagnosis of being in a vegetative state, her brain activity raises the intriguing (or disturbing) possibility that there is a fully conscious being locked in that unresponsive body after all. The scientists doubt this, pointing out that there is nothing wrong with her motor function, so if there really were a conscious being in there she would purposefully move at least her eyes. Cornell's Dr. Schiff suspects that she may at least be moving into "a minimally conscious state."
From the WSJ Science section: