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Friday, October 10, 2008

How Are Brains Structured?

FROM ROBERT LAWRENCE KUHN, HOST AND CREATOR OF CLOSER TO TRUTH: My inner self, my private sense of “I”—of this I am more sure than I am of anything else. How to understand this consciousness, this internal mental experience of an external physical world? What possibly could generate, create, cause it?
We know to begin with the brain. Biological brains are the most complex form of matter in the universe (as far as we know), and the human brain, three pounds, 75 percent water, is the pinnacle. How brains make their magic is just astonishing.
How to understand the brain? I start with brain structure, and to do so, I return to my roots, the Brain Research Institute at the University of California, Los Angeles, where more than 40 years ago I did my doctorate in brain research. Although my career went off in other directions, I’ve always followed advances in the brain sciences, and in my personal self-conception, if this means anything, I’ve always considered myself more as a lapsed brain scientist than an investment banker or writer.
I recently visited three of my former professors at UCLA, to whom I owe much: Carmine Clemente, a distinguished neuroanatomist whose research focused on central brain mechanisms related to sleep and wakefulness and behaviors like sexuality and feeding (he is also the editor of Gray’s Anatomy); Arnold Scheibel, a professor of neurobiology and psychiatry, and an expert in relating function and malfunction to the organization and structure of brain cells; and John Schlag, a neurophysiologist who has shown clear relationships between various motor behaviors and detailed electrophysiology of specific brain areas. It was wonderful seeing them again, and it made me realize once more how tightly brain and behavior are connected.
What is it about brain structure, I reflected, that can make all this consciousness and self and stuff happen? To oversimplify:

At the macro level of brain systems, it’s:
• symmetry and subtle asymmetries between sides—left and right brains are both similar and different
• specificity in function—different brain areas do different things
• plasticity in development—brains remodel and revise continuously.

At the micro level of brain cells, it’s:
• dozens of billions of neurons (nerve cells)
• trillions of connections between them
• incalculable permutations of electrochemical communications.

Christof Koch, a professor of biology and engineering at the California Institute of Technology, and a pioneer in investigating the “neural correlates of consciousness,” explains why the analogy of a brain to a computer falls off. In a computer’s central processing unit, the transistor equivalents are pretty much alike, whereas in a biological brain, there are many different kinds of nerve cells and different kinds of macro brain areas. This structure is a fundamentally distinguishing characteristic of biological brains.
And brain structure is not as rigid and inflexible as was once the accepted wisdom. New nerve cells are being created constantly in adults, and there is tremendous brain plasticity, as the fascinating work of Michael Merzenich of the University of California, San Francisco has shown, particularly in developing the basic science for cochlear implants, which enable deaf people to hear. (That the brain can learn to process input from artificial electronic signals and make them into meaningful sounds is remarkable evidence of the brain’s plasticity and adaptability.)
But our internal sense of “I,” believes Rodolfo Llinas, chairman of the department of physiology and neuroscience at New York University, is created by the cyclical waves of recursive feedback between the cerebral cortex (that covers the brain and accounts for the conscious registration of our senses, movements, and thoughts) and the thalamus (a kind of central relay deep in the center of the brain). Llinas calls this system the “I of the Vortex,” and he makes the claim that this is consciousness.
To understand consciousness, we know to begin with brain. The next question, to me, is as difficult to answer as it is easy to ask: Do we end with the brain? Most scientists, but not all, think surely so. Most theologians, but not all, think surely no. There is no compromise here.
I chose to study the brain because only by means of the brain can we know anything at all. Understanding the brain certainly brings us closer to truth. But, I wonder, will it ever bring us all the way to truth?

Robert Lawrence Kuhn speaks with
Carmine Clemente, Arnold Scheibel, John Schlag, Christof Koch, Michael Merzenich, and Rodolfo Llinas in "How Are Brains Structured?" the fifth episode in the Closer to Truth: Cosmos, Consciousness, God TV series, which airs Thursdays on the PBS HD network and many other PBS stations. Every Friday, participants in the series will share their views on the previous day's episode.