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MIND-BODY PROBLEMS

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same internal feelings. In his 1997 book The Mystery of Consciousness, Searle takes the experience of consciousness as a core reality precisely because it is an unmistakable interior event. His rebuttal of Dennetts ideas is curiously reminiscent of Descartess I think, therefore I am.Searle writes,

But where the existence of conscious states is concerned, you cant make the distinction between appearance and reality, because the existence of the appearance is the reality in question. If it consciously seems to me that I am conscious, I am conscious . . . it is just a plain fact about meand every other normal human being. . . . (Italics in original.)

Searle does not use this perspective to build a theory of con- sciousness, but Francis Crick explores such a theory in detail. In The Astonishing Hypothesis and elsewhere, and with his colleague Christoff Koch, he approaches the phenomenon through the binding problem in visual cognition.This particular function of mind draws on a large fraction of the brain, where certain groups of neurons deal with spe- cific parts of what we see, such as color, movement, and the edges of objects.The mind brings these elements together to produce an inte- grated visual understanding that is an important part of our mode of thought. Using a variety of evidence, Crick concludes that binding of this sort is produced by neurons located in different and specific parts of the brain that fire in a synchronized way, on average 40 times a second. He does not claim that this conclusion solves the problem of consciousness, but believes that the full answer must begin with just this kind of consideration of enormous numbers of neurons operat- ing together.

The Nobel Laureate neuroscientist Gerald Edelman, of Rockefeller University in New York City, and his colleague Giulio Tononi also consider the unified action of groups of neurons, most recently in their 2000 book A Universe of Consciousness: How Matter Becomes Imagination.Their theory draws on evolutionary development, which, they say, has formed our brains to process information more powerfully than human-made computers can. A kind of Darwinian survival of the fittest affects individual brains as well, through neu- ronal group selection:As a brain develops, the groups of neurons that survive are those that respond well to stimuli.They represent concep-

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