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"Consciousness," says Antonio Damasio, "is a concept of your own self, something that you reconstruct moment by moment on the basis of the image of your own body, your own autobiography and a sense of your intended future." Missing any one of the essential parts that it's built on diminishes consciousness but does not totally negate it. Damasio has no doubt that Boswell is conscious, though the quality of that consciousness is impossible for anyone else to imagine.
However, despite our every instinct to the contrary, there is one thing that consciousness is not: some entity deep inside the brain that corresponds to the "self," some kernel of awareness that runs the show, as the "man behind the curtain" manipulated the illusion of a powerful magician in The Wizard of Oz. After more than a century of looking for it, brain researchers have long since concluded that there is no conceivable place for such a self to be located in the physical brain, and that it simply doesn't exist.
But there is no shortage of competing theories about how consciousness might arise. One, offered by the Salk Institute's Francis Crick (co-discoverer of the structure of DNA) and Christof Koch, at the California Institute of Technology, is that consciousness is somehow a by-product of the simultaneous, high-frequency firing of neurons in different parts of the brain. It's the meshing of these frequencies that generates consciousness, according to Crick and Koch, just as the tones from individual instruments produce the rich, complex and seamless sound of a symphony orchestra. The concept is highly speculative, Crick acknowledges in his book The Astonishing Hypothesis (which carries the ironic subtitle The Scientific Search for the Soul). "If you think I appear to be groping my way through the jungle," he writes, "you are right."
New York University Medical School neuroscientist Dr. Rodolfo Llins also thinks coordinated electrical signals give rise to consciousness, though his idea is subtly different from Crick and Koch's. Llinas believes that the firing of neurons is not just simultaneous but also coordinated. Using a highly sensitive device called a magnetoencephalograph, which indirectly measures the electric currents within the brain, Llinas measured the electrical response to external stimuli (he used musical tones). What he observed was a series of perfectly timed oscillations. Says Llinas: "The electrical signal says that a whole lot of cells must be jumping up and down at the same time."
These oscillations, Llinas believes, are the basic building blocks of consciousness. What the brain does, whether asleep or awake, he notes, is make images. But these are purely mental constructions, even when they're based on external information. For example, says Llinas, "light is nothing but electromagnetic radiation. Colors clearly don't exist outside our brains, nor does sound. Is there a sound if a tree drops in the forest and no one hears it? No. Sound is the relationship between external vibrations and the brain. If there is no brain, there can be no sound."
The upshot, says Llinas: "We can say that being awake or being conscious is nothing but a dreamlike state." It is a state, Llinas concedes, that corresponds tightly to external reality. But it has no objective reality; as with a rainbow, you can perceive it but never actually touch or measure it.