AT THE HEART OF SCIENCE are judicious observations and measurements. This reality presupposes that something can be measured. But how can consciousness—the notorious ineffable and ethereal stuff that can’t even be rigorously defined—be measured? Recent progress makes me optimistic.
Consider a problem of great clinical, ethical and legal relevance, that of inferring the presence of consciousness in severely brain-damaged patients. Often the victims of traffic accidents, cardiac arrests or drug overdoses, such patients have periods when they are awake, and they may spontaneously open their eyes. On occasion, their head turns in response to a loud noise, or their eyes might briefly track an object, but never for long. They might grind their teeth, swallow or smile, but such activities occur sporadically, not on command. These fragmentary acts appear reflexlike, generated by an intact brain stem.
As many as 25,000 such “vegetative” patients in hospices and nursing homes hover for years in this limbo, at a steep emotional and financial cost. The extent of the damage and the persistent absence of purposeful behavior usually leave little doubt that consciousness has fled the body for good. Terri Schiavo was such a case, alive but unconscious for 15 years before her court-ordered death in 2005 in Florida.
Even worse, though, is the possibility that some of these patients may experience some remnants of consciousness, unable to communicate their feelings of discomfort or pain, agonizing thoughts or poignant memories to the outside world. Until recently, nothing could be done to diagnose when an awake mind was entombed inside a damaged brain.
Technology has come to the rescue with the demonstration—by Adrian M. Owen and his research group at the University of Cambridge—of awareness in an unresponsive patient with the aid of functional brain imaging. The patient, a young woman who sustained massive head injury as a result of a car accident, fulfilled all criteria for the vegetative state. In particular, she was unable to signal with her eyes or hands in response to commands. Owen placed the noncommunicative patient in a magnetic scanner and asked her to imagine playing tennis or to imagine visiting the rooms in her house. You and I have no trouble doing these tasks. In healthy volunteers given these instructions, regions of the brain involved in motor planning, spatial navigation and imagery light up. They did likewise in the unfortunate woman. Her brain activity in various regions far outlasted the briefly spoken words and in their specificity cannot be attributed to a brain reflex. The pattern of activity appeared quite willful, indicating that the patient was, at least occasionally, conscious but unable to signal this fact, more effectively cut off from her loved ones than any prisoner in solitary confinement. It may be possible to develop this technique into a kind of two-way radio between the patient and the rest of humankind.
It remains an open question how prevalent such a tragic condition—aware yet utterly uncommunicative—is. Brain scans of 17 vegetative patients have turned up only one other non-responsive patient with such a voluntary brain signal. Keep in mind, however, that absence of evidence is not evidence of absence and that the presence of consciousness will depend on the exact nature of the brain injury. The point I want to emphasize is that Owen and other researchers like him are developing scanning tools to spot consciousness without any external behavior.
Betting on Consciousness
The ultimate judge of any conscious feeling is the subject itself. This truism is used in everyday life: Can you see the angry face? Well, if you can’t, then you’re not conscious of it. This seductively simple strategy has drawbacks; in particular, people disagree on what exactly “consciously seeing” is if the face was only briefly flashed on a computer display screen. (Did you see any part of a face? Did you think you saw something like a face?) To get around this problem, neuropsychologists Navindra Persaud, Peter McLeod and Alan Cowey of the University of Oxford exploit gambling.