FROM ROBERT LAWRENCE KUHN, HOST AND CREATOR OF CLOSER TO TRUTH: We know what it means to see, hear, feel, and smell. We know, more than we know anything, what our “inner experience” feels like. Now, how is it possible that such inner experience is, literally, clumps of brain cells, their flowing chemicals and electrical impulses? The two things—inner experience and brain cells sloshing and sparking—seem so radically different!
So what is it about the brain that enables neuroscientists to claim they can explain the mind? And what is it about such scientific explanations of consciousness that some philosophers reject? This is the traditional “mind-body problem” in philosophy, an endless debate that has generated libraries of books.
For proper biologists, it used to be that studying the mind, or consciousness, was off limits, outside the scope of serious science, shunned. Scientists could tackle brain function, of course, determining which parts do what. But mind? Well, no, that was slippery, airy. Too loose. Too “philosophical.”
Christof Koch, a professor of biology and engineering at the California Institute of Technology, is a serious scientist who takes consciousness seriously. He seeks what he calls the “neural correlates of consciousness,” which generally means the kinds of electrical activities that occur in the brain each and every time that a certain conscious experience occurs. Koch has made the neural correlates of consciousness real science by bringing progressively greater precision to assessing what’s happening in the brain, in real time, when subjective experiences are sensed or felt.
When I did my doctorate in brain research at the University of California, Los Angeles 40 years ago, this was what I had dreamed of.
But correlation is not cause, as Koch is the first to point out. And the correlations thus far describe specific sensations, not a unified consciousness. But is there a real difference? Some say that consciousness is the illusory construct of multiple independent sensations fighting for attention like kids in a kindergarten. In philosopher Daniel Dennett’s formulation, consciousness is “fame in the brain.” If true, this demystification of consciousness would make the task of discovering its neurobiological basis much easier. In any event, can science, sticking with pure biology and its underlying chemistry and physics, produce a full theory of mind or consciousness?
Dr. Rodolfo Llinas, chairman of the department of physiology and neuroscience at New York University, has a full theory. He explains the swirl of consciousness by identifying it, quite literally, with swirling circuits in the brain—in particular, the recursive and continuous electrical circuitry between the thalamus, a relay and integration center in the middle of the brain, and the cerebral cortex, which controls the higher aspects of sensation and thought in the folds (gyri) and furrows (sulci) that cover the brain. To Llinas, these ceaseless upward and downward currents are not only how consciousness works, they are also what consciousness is. He calls it, “The I of the Vortex.”
Can brain-explaining-mind be that simple?
Before I inquire of philosophers, I must ask whether mind or consciousness can exist outside of biological brains. Is there anything special about biological brains? Can other kinds of “brains” also be conscious? My question—how can brain explain mind?—becomes more complex for highly advanced machines, or, as futurist and visionary Ray Kurzweil puts it, “nonbiological intelligences.”
Ultimately, says Kurzweil, these nonbiological intelligences will appear to be conscious: Every test of consciousness they will pass. They will be, or seem to be, no less conscious than your spouse, best friend, or children. There will be no way to tell the difference between a machine and a human. But are these nonbiological intelligences really conscious, with inner subjective experiences in their own private innards?
We can never know, says Kurzweil, not even in principle. I think he’s right: A true “consciousness detector” is, in principle, impossible to construct because it is always possible to give correct answers, no matter how detailed, without inner experience. For nonbiological intelligences, the crux of the problem will be the same as it is for the “other minds” problem in philosophy—how can one be absolutely certain that other people are conscious? The difference, of course, is that other people, other minds, are constructed like I am constructed, with wet brains or meat brains (choose your descriptor), and because I am sure that I am conscious, I can reason by analogy and become highly confident that other people are similarly conscious. But such wet-brain or meat-brain chauvinism masks the functional conundrum that if all functions are exactly the same, how then could the essence be different?
What then is mind? I’ve hit the limit in science. I turn to philosophy.
When I think of philosophy of mind, I think of John Searle at the University of California, Berkeley, who likes to follow the facts, wherever they lead. To Searle, it’s obviously false that consciousness doesn’t exist, and just as obviously false that consciousness is not part of the physical world.
To him, consciousness is real and irreducible, caused by brain processes, realized in the brain, and functions causally.
But if he’s right, I’m troubled. Because then, I think, consciousness would be the only thing in the universe that is “causally reduced” to brain function—meaning that the entire cause of mind is brain—but not “ontologically reduced” to brain function—meaning that the “being” or “essence” of mind is not brain.
Mind as caused entirely by brain? But not existing as brain? Can cause and existence be so radically different? What is going on here? Why should consciousness be so very special? And if consciousness is so very special, maybe its specialness goes beyond Searle’s somewhat subtle distinction.
I need something more. David Chalmers, an Australian philosopher of mind, has something more. Consciousness, he claims, is not an accidental derivative of reality working randomly but a fundamental part of reality existing permanently. For decades, there had been a progressive demystification of consciousness. Then, along came Chalmers.
To him, no matter how much neuroscience we learn, we will never explain consciousness. No matter how good the correlations of brain to mind, they could never literally be mind. There must be something extra in consciousness, which can never be explained by anything physical, chemical, or biological.
Chalmers gives me what I need. But what I think I need may be like a friend who is false; Santa Claus for a child.
So can the traditional mind-body problem be solved by science? For me, not so fast.
Most scientists explain mental activity in the purely physical terms of brain function, while others contend that consciousness must be generated by unknown, radically new kinds of laws. Still others wonder anew whether mind has existence beyond the brain and is a wholly different kind of stuff.
Can neuroscience explain consciousness, reducing mind to brain?
Or does mind maintain an independent existence, an irreducible element of reality?
Of only this I’m really sure: The choice is stark—mind is only brain vs. mind is more than brain. The dichotomy will lead us closer to truth.

Robert Lawrence Kuhn speaks with Christof Koch, Rodolfo Llinas, Ray Kurzweil, John Searle, Daniel Dennett, David Chalmers, and Alan Leshner in "Can Brain Explain Mind?" the 17th 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.