The New Yorker serves up a brilliant article this week on how fMRI scans of people in a “vegetative state” have revealed astonishing evidence that many have an active mental life, and some might argue may actually be conscious.
The findings are having powerful effect on not just the diagnosis of individuals with brain injuries, but the very concept of consciousness itself.
From these and other recent experiments, including his own, Naccache and his research team are developing a working medical definition of consciousness. “When we are conscious, the key property is our ability to report to ourselves or to others the content of the representation—as when I say, for example, ‘I am perceiving a flower,’ or the fact that I am conscious of speaking with you now on the telephone,” Naccache told me. “You have patients who are conscious, or who are able to make reports, but you can prove that some stimuli escaped their conscious reports, as in the case of blindsight or neglect. You can study the neural fate of these representations by showing that, even if the stimuli were not reported by the subject, they were still processed in the brain.” He added that, in the case of Owen’s vegetative patient who imagined playing tennis, it’s impossible to know whether she reported the event to herself—which would suggest that she is capable of conscious thought—or whether, as in the case of the blindsight and neglect patients, she had no subjective awareness of the experience. However, Naccache believes that consciousness also requires an ability to sustain a representation over time, which Owen’s patient clearly was able to do. “In assessing apparently vegetative patients who are unable to speak, and thus report, the direction of research should be to look for sustained representation,” he said. “If we can prove by neuroimaging techniques that this person is able to actively maintain a given representation during tens of seconds, it provides strong evidence of conscious processing.”
Naccache has recently incorporated a third neurological feature into his definition of consciousness: broadcasting. In a person who is conscious, he explained, information entering the brain is processed in a few areas and then distributed—or broadcast—to many others. “It’s as though there is a kind of ignition in the brain, and then information is made available to a very rich number of regions,” Naccache told me. “And that makes sense, that the information is initially represented locally and then made available to a vast network, because the person has this ability to maintain the representation within the network for a long time.”