The Frontier Within

By J. MADELEINE NASH

Contemplate for a moment a tangle of seaweed tossed up on the shore. This is what a neuron looks like, surrounded by a thicket of tiny tendrils that serve as communications channels. Now multiply that neuron 100 billion times. Crammed into the skull of every human individual are as many neurons as there are stars in the Milky Way. Each one of these receives input from about 10,000 other neurons in the brain and sends messages to a thousand more. The combinatorial possibilities are staggering. The cerebral cortex alone boasts 1 million billion connections, a number so large, marvels neuroscientist Gerald Edelman in his recent book about the brain, Bright Air, Brilliant Fire, that "if you were to count them, one connection per second, you would finish counting some 32 million years after you began."

Assembled by nature and honed by evolution, the convoluted 3-lb. organ positioned between our ears represents a triumph of bioengineering, one that continues to elude comprehension and defy imitation. "The brain," declares molecular biologist James Watson, co-discoverer of the physical structure of DNA, "is the most complex thing we have yet discovered in our universe." The + quest to understand the biology of intelligence is likely to occupy the minds of the world's best scientists for centuries to come. The task may prove more challenging than those alive today suppose, requiring perhaps new breakthroughs in physics and chemistry. Meanwhile, the knowledge spawned by this search promises to transform society. Here is what lies ahead:

COMPUTERS WILL EMULATE THE BRAIN BUT NOT REPLACE IT

From the wheeled cart to the printing press, from the telephone to the airplane, inventions have enormously expanded the repertoire of human capabilities, and this trend will continue, even accelerate. In this century computers have provided instant access to awesome number-crunching power and a vast storehouse of information. In coming centuries they will augment and amplify human skills in far more astounding ways. Thus, while the brain will not undergo much in the way of biological evolution, humans, assisted by ever more powerful computers, will become capable of far greater intellectual feats. "We won't recognize any difference in brains themselves," emphasizes Maxwell Cowan, chief scientific officer of the Howard Hughes Medical Institute in Bethesda, Maryland. "But we will recognize enormous differences in what brains know and understand."

Intriguingly, the brain's expanding knowledge of itself has begun to suggest radical new approaches to computer design. Like the brain, the computers of the future will not execute tasks in serial lockstep but will be capable of doing a million things in parallel. The chips of which they are composed may well be silicon, but they will mimic biological systems in almost every other way. A tantalizing hint of what the future holds comes from a type of computer known as a neural network. Employing the time-tested tactic of trial and error, these assemblages of artificial neurons have already "learned" to recognize scribbled handwriting, deduce principles of grammar and even mimic the acoustic sensitivity of the barn owl. By cobbling several of these sensory systems together, scientists will certainly be able to create, say, a robot that combines a barn owl's hearing with the ability to track moving objects and issue an ear-piercing hoot. Home gardeners may well employ an artificial owl to chase away rabbits and deer, but they will hardly consider it an intellectual equal. "Let me put it this way," laughs Caltech physicist Carver Mead, a legendary designer of computer chips. "Two hundred years from now, I will not be having this conversation with a piece of silicon."

THE DEAF WILL HEAR, THE BLIND SEE, THE LAME WALK

By the end of the next century, if not before, scientific insight into the perceptual centers of the human brain should vanquish these ancient afflictions. Already scientists have developed a cochlear implant that bypasses nonfunctioning hair cells in the ear and stimulates the nerve leading to the auditory cortex of the brain. Says Michael Merzenich, a neurophysiologist at the University of California, San Francisco: "We know that these inputs to the brain are distorted, yet the patients who have worn them for a while insist that what they hear sounds perfectly normal." What appears to occur, says Merzenich, is that the brain somehow manages to adjust its connections to make sense of the distortions it receives. This clear demonstration of the plasticity inherent in the adult brain lends hope that scientists of the future will succeed in performing other similar feats. One of these might well be the ability to equip artificial limbs with electronic "neurons" that can respond to signals relayed by the brain. These circuits might even include the equivalents of the axons and dendrites that link one neuron to another.

Almost certainly, scientists will master techniques for stimulating injured neurons to regenerate themselves. The brains and spinal columns of adult mammals do not possess this ability, at least not yet. A clue that this should be possible comes from frogs and salamanders, whose central nervous systems miraculously regrow following injury. Scientists have discovered several proteins that may eventually be deployed to rejuvenate broken spinal cords and damaged optic nerves. "I don't hold out too much hope for bionic man," says Michael Stryker, a colleague of Merzenich's who specializes in vision. "I think we will get there faster using biological techniques."

GENETIC ENGINEERING WILL EXTEND TO MENTAL TRAITS

Scientists are currently absorbed in tracking down genes believed to be responsible for such mental illnesses as manic depression and schizophrenia. Eventually, they can be expected to broaden their goals and seek out the genetic tool kit for building such intellectual traits as musical talent, mathematical genius and, above all, personality. Shyness, for instance, appears to have a genetic basis; assertiveness and hair-trigger anger probably do as well. Like it or not, predicts Dr. Lewis Judd, chairman of the psychiatry department at the University of California at San Diego, "We are going to find that the attitudes we take, the choices we make, are far more influenced by heredity than we ever thought."

For the next century or two, if not beyond, schemes for improving the brain through genetic tinkering are likely to be confounded by a combination of social taboos, legal restrictions and sheer biological ignorance. But when the genes that underlie personality and behavior are isolated and understood, society will reach a critical ethical divide. A Pandora's box of options that were not available in centuries past will suddenly pop wide open. Should would-be parents who learn a fetus has inherited a strong likelihood of developing a serious but treatable mental illness opt for an abortion? Should they choose gene therapy to replace the defective DNA in their newborn child's brain cells? And while they're contemplating all this, might they not also consider conferring on their offspring desirable traits like intelligence?

MIND READING WILL BE MORE THAN A PARLOR GAME

The machines that make images of the brain today are large, expensive contraptions that only major medical centers can afford. But just as computers have become ever smaller, cheaper and more powerful, so will the ultrafast successors to present-day positron-emission tomography and magnetic-resonance imaging scanners. Washington University neurologist Marcus Raichle predicts, in fact, that the "brain scopes" of the future will make a big splash at Disneyland and other theme parks. One can imagine lines of vacationers waiting to have their thoughts and emotions imaged in garish hues.

But these machines will also be put to serious purpose. Consider, for example, the tantalizing evidence that certain patterns of brain activity correlate with higher achievement levels. Competing educational strategies might someday be judged by whether they stimulate specific areas of the brain and how strongly. "Is phonics really the best way to teach reading?" muses Dr. Raichle. "Or is it just another silly idea? By looking at the brain, I think we'll discover the answer to that question." And to others as well. Many mothers-to-be have wondered whether playing music and reciting poetry can influence embryonic brain development in desirable ways. Someday they may be able to judge for themselves.

More important, tomorrow's brain scanners will be able to assess intellectual strengths and weaknesses in preschool children. A wide spectrum of mental weaknesses will become targets for early intervention. Dyslexia could be diagnosed in infancy, the time when brain plasticity is highest. Therapies could then be monitored by charting changes in neuronal firing patterns.

BRAINS WILL BE HEALTHIER, HAPPIER

Prominent mainstays of the pharmacopoeia of the future will be compounds that prevent nerve cells from dying. Much of the devastation caused by stroke is believed to occur because the directly injured neurons release massive quantities of the neurotransmitter glutamate. Normally, tiny bursts of glutamate act as signals between one neuron and another, triggering the brief opening of minuscule channels that allow calcium to pass through the cell's protective membrane. Too much glutamate, however, causes the channels to remain open too long, permitting an abnormal, and lethal, influx of calcium. Soon drugs that mop up excess glutamate or block its action may make this sort of stroke-related brain damage as preventable as tissue damage from gangrene. Similar strategies should likewise succeed in protecting neurons from the ravages of Alzheimer's disease.

Needless to say, expanding knowledge of the brain's complex biochemistry and how it goes awry will bring about more effective treatments for depression and schizophrenia, panic attacks and obsessive compulsions, alcoholism and drug addiction. Along the way, scientists will gain profound insights into the biochemical signals that create the astounding range of human emotions. "Which peptides make you sad, which ones make you happy, and which ones make you feel just grand?" wonders Columbia University neuroscientist Eric Kandel. That knowledge could conceivably translate into an ability to fine- tune those states at will -- through either pharmacology or sophisticated biofeedback techniques.

Certainly nothing in the past 100,000 years of cultural evolution can prepare future generations for the moment when science lays bare, as it most certainly will, the secrets of the human mind. "We will be rendered naked," predicts Tufts University philosophy professor Daniel Dennett, "in a way that we've never been naked before. The mind boggles at the varieties of voyeurism, eavesdropping and intrusion that will become possible." Concepts like good and evil, free will and individual responsibility, will presumably survive the upheaval, but not before being shaken to their deepest foundations. Imagine, for a moment, that a psychiatrist could peer into the psyche of a serial killer. Could the doctor see what was wrong? If he could, would he know how to fix it?

The great adventure on which modern neuroscience has embarked will end up challenging our most cherished concepts of who we are. "In the end, we will even figure out how this tissue in our skulls produces the states of self- awareness we refer to as consciousness," ventures John Searle, a philosopher of science at the University of California, Berkeley. But just as understanding the Big Bang has not permitted humans to create new universes at will, understanding consciousness will probably not allow us to construct an artificial brain. Besides, says University of Iowa neurologist Dr. Antonio Damasio, "a brain is not likely to work without a body." At the very least, a disembodied brain would be extremely disoriented and terribly unhappy.

In the coming centuries, one imagines, the desire to create monstrous caricatures of ourselves will dissipate. At long last, we will reclaim the awe and wonder our predecessors reserved for machines and turn them back toward our biological selves. Like Narcissus, we will behold the image of our minds and lose ourselves in endless admiration.