Brain scientists will tell you that the greatest problem facing human biology, and perhaps all of science, is cracking the code of consciousness. It means solving the long-intractable brain-mind conundrum: How does our material brain--the most complex physical system known--produce our immaterial but vital sense of awareness? Neuroscientists and philosophers argue fiercely about how to solve the riddle and whether it is even solvable. Some say consciousness is illusory. (Try to counter that one--a real headache.) Others say consciousness exists but at too complex a level for humans to fathom, like quantum mechanics is for monkeys. Still others believe consciousness will yield its secrets only when we discover new physical brain laws that could reveal its creation.

Christof Koch rejects all this skepticism. As one of the world's leaders in the field, the California Institute of Technology neuroscientist believes that consciousness is distinctly physical, that it can be described by existing neurological theories, and that he is on the way to figuring it out. He has some invaluable help in collaborators such as Tomaso A. Poggio, the neural-networks and artificial-intelligence guru at the Massachusetts Institute of Technology, and some lasting inspiration instilled by his close friend and longtime collaborator, the late Francis Crick, who with James D. Watson won the Nobel Prize for discovering the double-helix structure of DNA. The key to finding an answer, Koch says, is to trace the activity of neurons--the "neural correlates"--of the simplest type of consciousness, which is the awareness of something we see. "Some of my colleagues think I'm naive," Koch remarks, "that this rather narrow focus won't reveal the workings. And they might be right. But as a scientist, I think this is the most likely way to solve this problem."

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