A Mind for Consciousness
Somewhere in the brain, Christof Koch believes, there are certain
clusters of neurons
LOS ANGELES--Prominent on Christof Koch's desk is a white ceramic phrenology bust, its skull divided by glazed black lines into arbitrary regions. The maverick neuroscientist assures me that I need not worry about any caliper exam; he is as bemused as the rest of us by Lorenzo Fowler's 19th-century phrenological propaganda that cortical areas correspond to such personal attributes as "love of country" and "secretiveness." But Koch appreciates the early brain map as a reminder that he's looking for "a discrete set of neurons that might be in 20 different areas but share some set of properties that are responsible for generating consciousness."
Neurobiologists have since given up the notion that Koch may be dangerously offbeat, despite his having tattooed his arm last summer with the Apple Computer logo to demonstrate his love of the Macintosh (a zeal not even matched by Steve Jobs). The neuroscientist leads about 20 researchers and calls their mission to explain consciousness "one of the major unsolved problems of modern science."
During his early years, Koch, the American-born son of German diplomats, imbibed embassy life from Kansas City to Amsterdam to Bonn, Ottawa and Morocco. Initially he wanted to be a cosmologist, but he realized that his gifts were not in high-level mathematics. Two books sparked his interest in nervous system computations, one of which gave a physicist's perspective on the brain. Its author, Valentino Braitenberg, became one of Koch's advisers at the Max Planck Institute for Biological Cybernetics in T黚ingen, Germany, where Koch earned a doctorate in physics in 1982.
Koch started thinking about consciousness seriously in the summer of 1989--thanks to a throbbing toothache. He wondered, Why do a bunch of neurons flashing around result in pain? And why don't electrons moving in a transistor cause the computer to have subjective states? By that time he and Crick, one of DNA's co-discoverers, had already had several discussions along these lines (they had met incidentally in Europe and become friends). They soon drafted their first joint paper on consciousness.
Visual awareness is Koch's chief pathway into the murky workings of the mind. Not only is vision readily manipulated and the best understood of the senses, but it also shares fundamental aspects among species ranging from fruit flies to humans. Such commonalities are important to Koch because he believes (to the chagrin of many philosophers) that facets of consciousness--visual, olfactory, linguistic, even self--are all "elaborations of a common biological process." Koch has used electrophysiological recordings and brain imaging in primates to explore the neuronal operations underlying vision.
Along the way, his vision work has helped elucidate how neurons compute. Koch was among the few to challenge the prevailing metaphor equating the wiring of the human brain with the circuitry of a computer. Instead of accepting the idea that thought results from the combined action of billions of neurons, each a relatively simple component, he asserted that individual neurons carry out complex computations.
Indeed, mounting evidence shows how neural cells function not only as a network of linear threshold devices, relaying electrical pulses or not, but also as individuals working autonomously and adaptively. Neurons can add signals, subtract them, multiply, divide, filter and average them, among other functions. "The computational toolbox of individual neurons dwarfs the elements available to today's electronic circuit designers," Koch says.
To test such notions, Koch is focusing on the cagey mind of the rodent. His team aspires, among other things, to create "zombie" rodents by inactivating specific subpopulations of neurons, thereby dissociating the animals' behavior and awareness. In this way, neurons critical for awareness may become apparent. (But first the team must show that rodents are indeed conscious, through experiments based on a more complex version of Pavlovian conditioning called trace conditioning.) Unraveling basic neural correlates, Koch believes, will definitively answer such questions as whether human babies are conscious.
When it comes to a grand unified mind and brain theory, or GUMBAT, in Koch's lingo, Koch and Crick feel that humility is in order. "The last 2,400 years--starting with Socrates, Plato and Aristotle--have shown the futility of developing grand-scale theories," Koch says. "Right now we feel we lack basic elements for any such theory." He equates pursuing a global model now with "Aristotle's chances of developing a good theory of heredity in his day."
Not all leading consciousness researchers think that locating specific neuron groups is the key. Edelman and his longtime collaborator Giulio Tononi, now at the University of Wisconsin朚adison, see limits. "Even if we could come down with a small list [of neurons]," Tononi says, "we wouldn't understand why some neurons contribute to the whole experience of consciousness and others don't. The apparent differences seem insufficient to explain the metaphysical gap." Tononi and Edelman favor characterizing broader neural processes to account for properties of consciousness--namely, differentiation (neural complexity) and integration (functional clustering). That is, a huge number of conscious states exist, and each is a unified whole that can't be subdivided. These two properties, they contend, can be measured to gauge whether a group of neurons is contributing to conscious experience. The combination of neural complexity and functional clustering forms the basis of their so-called dynamic core hypothesis.
Meanwhile a chorus of philosophers led by David Chalmers of the University of Arizona believes that a scientific theory of consciousness will emerge but that it won't be just a neurophysiological theory. "It's very much an open question what form" a theory of consciousness will take, Chalmers remarks. Before a theory can take hold, he and Roger Penrose of the University of Oxford propose that new physical laws or principles will need to be discovered. That's because consciousness, they say, is an irreducible phenomenon, much like space, time and gravity.
Koch acknowledges the difficulties in developing a neurophysiological explanation of subjective experience but thinks neuroscience will eventually solve the puzzle. "Whether we will ever have a satisfactory reductionist account, like we think we do of life, remains an open question," he says. Then he points to a bit of wisdom from renowned English biologist J.B.S. Haldane. "The universe is not only a strange place," Koch paraphrases, "but a stranger place than we can imagine."Julie Wakefield is a science writer based in Washington, D.C.
--By JULIE WAKEFIELD
Julie Wakefield is a science writer based in Washington, D.C.