This incident occurred more than three decades ago, when Dr. Antonio Damasio was a medical student in Lisbon, Portugal, and he has never forgotten it. How was it possible, he wondered, for someone to be there and yet not be there, to be awake and yet not be awake, to be aware of his surroundings and at the same time be oblivious to them? The more Damasio puzzled over what had happened to the patient during an epileptic seizure, the more he felt compelled to confront a much larger question: What is it about the human brain and its networks of neurons that give rise to consciousness?
In recent years scores of scientists have grappled with that profound question, among them mathematical physicist Roger Penrose, biologist Francis Crick and psychiatrist Allan Hobson, as well as many philosophers. Their answers have ranged from the optimism of Tufts University's Daniel Dennett, who says consciousness will one day be understood as nothing more complicated than a kind of biological software routine, to the outright pessimism of Rutgers University's Colin McGinn. He regards consciousness as "the ultimate mystery, a mystery that human intelligence will never unravel."
Now it's Damasio's turn. In a new book titled The Feeling of What Happens (Harcourt Brace; $28), the noted neuroscientist not only argues that human consciousness is comprehensible but also offers an arrestingly original explanation of its workings. What makes his views so noteworthy is that they're grounded not in theoretical musings but in years of clinical research on patients who are epileptic or have suffered brain damage through strokes, disease or traumatic injuries.
From these studies, Damasio, who is chairman of the University of Iowa's neurology department, concludes that consciousness is a layered edifice, like some Mayan pyramid or Mesopotamian ziggurat. It is based on an inchoate feeling of self that arises from the brain's detailed "diagram" of the body. Damasio says this diagram, which is continuously revised by the senses, can be thought of as the "protoself"; it props up the rest of the structure.
All kinds of creatures, even ones as lowly as snails, have protoselves, Damasio says, but they aren't really conscious. Consciousness, he explains, requires a nervous system sufficiently evolved and complex that the organism can hold in mind the image of a protoself's moving through and interacting with the world.
It's this core consciousness, as Damasio calls it, that registers "the feeling of what happens," and it's something we share with other intelligent animals, such as dogs. But there is another form of consciousness that embellishes one's image of self with a wealth of autobiographical detail. Damasio calls this extended consciousness, and it requires such a vast capacity for memory that it's probably special only to humans and great apes. Hence, damage to the brain's memory centers can impair a person's extended consciousness while leaving core consciousness intact.
Damasio cites the case of a young woman who at age 30, shortly after the birth of her second child, entered a netherworld of nonstop epileptic seizures. The seizures damaged a region of the brain called the hippocampus, so that afterward she could no longer recall the simplest things, like having put clothes in the washer or having given her kids permission to visit friends. For six years she has lived in a free-floating present, unable to form new memories or envision the future. Her extended consciousness has been sadly diminished.
To Damasio and his wife Hanna, his closest collaborator, such patients are windows into the brain. Their seizures, strokes and diseases, while damaging the hippocampus, leave core consciousness unimpaired. That's because it evolved much earlier than extended consciousness, Damasio says, and thus is dependent on more ancient structures, especially those located within the brain stem and hypothalamus. Among the most important: a large region called the cingulate cortex, which not only receives sensory input from the skin, muscles and internal organs but also sends out signals to initiate movement and focus attention, as when emotions send our blood pressure soaring or make our hair stand on end.
As a demonstration of the cingulate cortex's importance to consciousness, Damasio recalls a patient he calls L. After a comparatively minor stroke, she became bedridden, lying utterly still and mute for six months even though her physical condition seemed to suggest she could have resumed her daily life. During her ordeal, she later told Damasio, she felt absolutely no desire to speak or move. "Her mind," he says, "had not been imprisoned in the jail of her immobility. Instead it appeared that there had not been much mind at all, and nothing that would resemble consciousness." It turned out that she had done damage to her cingulate cortex.