Understanding how neurons operate is one thing; understanding how they make us the conscious beings we are is another matter
By STEVEN PINKER
Imagine this scene from the future. You are staring at a screen flickering with snow. Scientists have hidden one of two patterns in the dots, and eventually you spot one. But you don't have to tell the scientists what you are seeing; they already know. They are looking at the electrical signals from one of the billions of cells in your brain. When the cell fires, you see one pattern; when it stops, you see another‹your awareness can be read from a single neuron. Now, in an even more unsettling trick, they send an electrical current to the neurons in that part of your brain and, with a push of a button, make you see one pattern or the other.
These feats of pinpoint mind study are not fantasies. They have already been performed by the Stanford neuroscientist William Newsome. Not with people, of course, but with monkeys. Yet few scientists doubt the trick would work with us.
This is just one example of how much we have learned about the workings of the brain in the past 10 years‹a period of intense research proclaimed by the U.S. Congress and the President as the Decade of the Brain. Every facet of mind, from mental images to the moral sense, from mundane memories to acts of genius, have now been tied to tracts of neural real estate. Using fmri, a new scanning technique that measures blood flow, scientists can tell whether the owner of the brain is imagining a face or a place. They can knock out a gene and prevent a mouse from learning, or insert extra copies and make it learn better. They can see the shrunken wrinkles that let a murderer kill without conscience, and the overgrown folds that let an Einstein deduce the secrets of the universe. How far will this revolution go? Will we ever understand the brain as well as we understand the heart, say, or the kidney? Will mad scientists or dictators have the means to control our thoughts? Will neurologists scan our brains down to the last synapse and duplicate the wiring in a silicon chip, giving our minds eternal life?
No one can say. The human brain is the most complex object in the known universe, with billions of chattering neurons connected by trillions of synapses. No scientific problem compares with it. (The Human Genome Project, which is trying to read a long molecular string composed of four letters, is a snap by comparison.) Cognitive neuroscience is attracting so many brilliant minds that it would be foolish to predict that we will never understand how the brain gives rise to the mind. But the problem is so hard that it would be just as foolish to predict that we will.
One challenge is that we are still clueless about how the brain represents the content of our thoughts and feelings. Yes, we may know where jealousy happens‹or visual images or spoken words‹but "where" is not the same as "how." We don't know how the brain holds the logical connections among ideas that spell the difference between "Burr slew Hamilton" and "Hamilton slew Burr," between the image of a woman winking to realign her contact lens and that of a woman winking to flirt. These distinctions don't appear as blobs in a brain scan. They arise from the microcircuitry of the living human brain, and most people don't want to donate their brains to science until they are dead. (As Woody Allen said, "It's my second-favorite organ.") The content of our thoughts may be the province of psychologists studying the brain's software, rather than neurobiologists studying its hardware, for a long time.
Another challenge is understanding how the mere darting of ions and oozing of neurochemicals can create the vivid first-person present-tense subjective experience of colors, sounds, itches and epiphanies that make up the self‹the soul, if you will. There's no doubt that physiological brain activity is the cause of experience. Thoughts and feelings can be started, stopped or altered by electricity and chemicals, and they throw off signals that can be read with electrodes and other assays. I also have little doubt that we will crack the mystery of consciousness, learning which brain events correlate with experience. Just compare brain activity when a person is awake or anesthetized, or when a novice is thinking about his golf swing and when a pro does it automatically.
But why some kinds of brain activity feel like something to you‹or, more accurately, are you‹is another question, and scientists disagree about how to answer it. Some say that subjective experience is unobservable and not a proper topic for science. Some say that once we can distinguish conscious brain processes from unconscious ones and show how they cause behavior, there is nothing left to explain; people who are looking for some extra ingredient are just confused. Some concede that sentience is still a mystery, but expect that an unborn genius will someday explain it to us as all. Still others suspect that the brain did not evolve to grasp the answer, any more than it can visualize what came before the Big Bang or the shape of a curved 4-D universe. If you think the answer is obvious, you are prepared for the ultimate triumph of the brain science of tomorrow. The synapse scanner has been perfected, and you can download a backup copy of your mind into a brainlike computer that will outlast your body. Unfortunately the scanner destroys the tissue it scans, so you have to choose between your old brain and a new one. The new brain will react and behave exactly like you‹but would it be you? If you say yes, are you confident enough to step into the scanner?