We like to think of ourselves as the top of the line, the epitome of a long lineage of human beings. But we still have a lot to learn about our brains and our bodies.

Not too long ago breaking the four minute mile was thought to be impossible. But once that barrier was breached by Roger Bannister in 1954, it set the stage for the rise of the superathlete. Today runners routinely run a mile in less than four minutes and every Olympics sees old records smashed.

A similar phenomenon is happening to the brain. Not too long ago the brain was considered to be hard-wired. For the most part, people were not concerned about the development of a child's brain until he or she went off to school.

Scientists are finding that this notion is as much of a myth as the unbreakable four-minute mile. There is a growing recognition today that the kind of experiences the brain is exposed to in the first three years dramatically influence how it operates-for the rest of its life.

Some revolutions are obvious because they are fought with weapons. Others, especially those that require new ways of thinking, tend to sneak up on us. The revolution in brain research is only now revealing itself. For the past 5 to 10 years scientists have been busy figuring out how the brain gets built, how it gets damaged and how it can be repaired.

At the core of this new knowledge is the plasticity factor, a term that scientists use to describe the brains amazing ability to constantly change its structure and function in response to experiences coming in from the outside. They recently discovered chemical lifesavers inside the brain called neurotrophic factors, which are critical for the development and maintenance of brain cells. Scientists are searching for ways to replenish these vital chemicals when they decline with age.

With the growing understanding of how the brain works comes the opportunity to increase brain power. Who wouldn't want to improve their memory, stop forgetfulness and prevent Alzheimer's disease and other neurodegenerative disorders. For me this is the best time to be a science writer because the powerful new tools of molecular biology and genetic engineering are revolutionizing most fields.

Look what's happened to cancer. Ten or so years ago cancer was thought to be more than 100 different diseases and scientists didn't' t think they would ever understand it. But, using molecular biology's new tools, they have solved cancer's mystery. Cancer is a derangement of normal genes. In a sense, we all carry the seeds of our own cancers in our genetic codes.

How does that happen? Genes that promote cell division can cause cancer when they forget to turn off. They are like accelerators stuck to the floor. But cancers can also result when the brakes fail, as when genes that are supposed to regulate cell division fall asleep on the job.

Turning those same tools loose in neuroscience is producing a similar revolution. Scientists have learned more about the brain in the past 5 years than in the last 100. The explosion of new knowledge has led scientists to a greater understanding of the brain's biology and to finding potential causes of violence. What we thought we knew about the relationship between a deprived or bad upbringing and the increased risk of criminal behavior is now being traced to the brain's chemistry. It is the biological smoking gun of violence. We are now finding the molecular answers to the things that happen to the brain that we could only grope for with older techniques - such as psychology, psychiatry, and sociology.

Now we can see thoughts with new imaging devices that can spy on the living, working brain, and we can eavesdrop on individual brain cells to listen to their chatter. With this new technology we can begin to understand through genes, chemistry and experience the sayings, which were based only on observation, "the child is father to the man" and "as the twig is bent, so grows the tree." It also is evident now why a child can easily learn a new language in a foreign country, if he or she does so at the age when the brain cells that process language are being wired.

And this new knowledge puts to rest the old, contrived argument of which is more important, nature or nurture, genes or environment. Do we come into the world fully programmed to act the way we do or are we blank slates waiting to be written upon? The answer is that genes and environment are probably equally important. The environment affects how genes work and genes determine how the environment is interpreted.

Most people are delighted with all the new information about the organ that is most curious to us. But some don't believe it and others are afraid of it, convinced that such research is a plot to discriminate against some groups, or gain mind control over others.

I suppose it is somewhat disconcerting to realize that our thoughts are created by molecules and that the molecules are manipulated by our experiences. But, instead of being limiting, or threatening, I believe the new knowledge about the brain is enlightening and liberating.

My foray into this revolution began in 1992 when then editor of The Chicago Tribune, Jack Fuller, was getting ready to launch a year-long project called "Killing Our Children." He asked if there was anything going on in brain research that might be helpful. For me that was like being given the keys to the candy store.

As I began to dig in, what initially turned me on was the work of the University of Chicago's Peter Huttenlocher. He was, for the first time, counting synapses, the telephone lines that enable brain cells to communicate with each other. These connections are so small and so numerous that they had previously defied a scientific census.

From autopsies of the brains of fetuses and people ranging in age from a few months to their nineties, he took samples about the size of the head of a pin, each containing about 70,000 brain cells. In a sample from a 28-week-old fetus he found 124 million connections between the cells. The same size sample in a newborn had 253 million synaptic connections and in an 8 month old the number exploded to 572 million.

At the fastest rate, connections were being built at the incredible speed of 3 billion a second, eventually reaching a total of about 1,000 trillion connections in the whole brain. After that point, the connections begin a gradual decline. By about age 10 or so, half the connections have died off, leaving about 500 trillion, a number that remains fairly constant through most of life.

Obviously something pretty terrific was going on.

I then became curious about what was happening to the brain cells themselves. I learned that scientists had found a similar explosion there, but it occurred during fetal development. From conception to about halfway through fetal life, brain cells grow from one to about 200 billion. Then brain cells begin to die off, leveling off at about 100 billion at birth, the number that remain through adulthood.

Again, something amazing was happening. Both phenomena were examples of genetic frugality. Humans do not contain anywhere near enough genes to make a fully operational brain at birth. So they are given an overabundance of the same or similar cells and connections between them and the brain then has to learn how to make itself work.

A surplus of brain cells makes sure that there are enough available for the awakening body to plug into to make the heartbeat, muscles twitch, lungs breathe and eyes move. Brain cells compete for the jobs. It's as if they all come out of the same mold but have to learn different jobs, depending on where they find themselves. Those cells that don't connect die off. There is some thought that the extra cells also give the brain the ability to evolve new capacities, such as language and abstract thinking.

A similar thing happens to the synaptic connections after birth. Twice as many are made to guarantee that a newborn will be able to receive input from any environment it is born into, whether it's Chicago or Calcutta, and to adapt to the food, language and culture.

The outside world shapes the brain's architecture. The connections that do not become part of this structure perish. The outside world comes in through the senses---vision, hearing, smell, touch, taste---teaching the brain what to become.

As I continued my research, other pieces of the puzzle began to fall into place.

One was a fairly old piece. In the 70s Torsten Wiesel and David Hubel sewed shut one eye of newborn kittens. Two weeks later the eyes were opened. Although anatomically perfect, the eyes that had been closed could not see.

It was the most vivid evidence that there are critical stages of development in which the brain needs the-right kind of outside stimulation to teach brain cells how to do their jobs. In this case it was vision. But it is also true for speech and other functions.

During critical developmental periods, brain cells that normally process vision do not learn how to do so if no visual stimuli come in to activate them. They either go off to perform another job, such as helping to process information coming in through the uncovered eye, or they shrivel and die.

This discovery had an immediate impact on children who are born with cataracts. Doctors used to wait until the children were older and stronger before removing-the cataracts. They found, to their dismay, that while the children's eyes were perfect, they couldn't see. The same thing that had happened to Wiesel's and Hubel's cats was happening to these children.

Learning that early visual stimulation was essential for the cells in the visual cortex to be able to see, surgeons began removing cataracts as soon after birth as possible. Today thousands of children born with cataracts have sight who otherwise wouldn't. That's something to remember when you think about the need for animal research.

Another piece of the puzzle was provided by Bill Greenough of the University of Illinois. He exposed one group of rats to a stimulating environment---toys, colors, playmates, exercise devices, challenges. A comparison group of rats was housed in routine laboratory cages with little stimulation.

When Greenough looked at the brains of the animals in the two groups he found the key to building brain power. The animals living in the stimulating environment had 25 percent more connections between their brain cells than the control rats, and they were a lot smarter.

For a human being, that translates into trillions of extra connections---and remember, connections mean brain power---and possibly a boost in IQ of 20 points or more.

What Huttenlocher was seeing in his autopsy studies, and Greenough, Wiesel and Hubel were seeing in animal studies, researcher Harry Chugani was seeing in people.

Using PET scans, which can follow the chemistry of thoughts in living brains, Chugani found that the brain is superactive from the ages of 4 to about 10, the years in which brain cells are vigorously learning which connections to keep and which to discard. These are the wonder years of learning, when a child can easily pick up a foreign language without an accent and learn a musical instrument with ease. You can learn a foreign language in adulthood, but it is much harder and you will have an accent. Responding to these new findings about the role that the environment plays in physically shaping the brain, especially during the critical periods of development, the National Institute of Mental Health has refocused its mission. Its goal now is to promote earlier and earlier intervention strategies to prevent some of the bad things that are associated with stressful environments during childhood.

In its recent report, Starting Points, the influential Carnegie Corporation of New York said the first three years of a child's life are vitally important to brain development. Unfortunately, for a growing number of children the period from birth to age three has become a mental wasteland. Society, said the Carnegie report, needs to invest adequate resources in helping these children at this critical period in their lives if we are to stem the growing epidemic of violence.

There is increasing concern that the lack of proper stimulation, may be damaging brains. The same may be true of too much exposure to the wrong kind of stimulation, such as violence. Indeed, in the last 25 years there has been a doubling, of the rates of crimes of violence, depression, suicide, and drug and alcohol abuse.

The culprit, many scientists now fear, may well be brain cells that do not learn what they are supposed to do because they have been deprived of normal stimulation on the one hand and overexposed to violence and stressful events on the other.

For millions of American children the world they encounter is relentlessly menacing and hostile. So, with astounding speed and efficiency, their brains adapt in an effort to protect them by preparing for battle. Cells rewire trillions of connections that create the chemical pathways of aggression.

But the brain does not have to be victimized. It can be prevented from going down the wayward path.

Craig Ramey of the University of Alabama showed that what Greenough did with animal brains by providing stimulating experiences, he could do with children. Starting as early as 6 weeks of age, his intervention program showed that impoverished children exposed to nurturing and mentally stimulating experiences could be prevented from having low IQ's and mental retardation.

After 3 years children in the intervention group had IQs in the normal range, around 100, whereas children living in similar poor neighborhoods, but who were not in the intervention program, averaged IQs that were 20 points lower.

By age 12, 50 percent of the children in the control group, those who continued to live unstimulating lives, had failed one or more grades. But only 13 percent of the children in the intervention group had a similar failure record.

Early intervention also seems to work on middle class children. Using Ramey's stimulating learning experiences, Jeanne Brooks-Gunn of Columbia University's Teachers College wanted to find out if she could raise the IQs and reduce behavioral problems of premature infants, who come into the world at a biological disadvantage.

In a study of nearly 1,000 premature infants at 10 centers, those in the intervention group had modest, but significantly higher IQs than infants in the control group after three years.

Importantly, her study included middle class families as well as poor ones, a spectrum that other intervention studies had not looked at. It also included middle class blacks and poor whites. These across-the-board intellectual and behavioral improvements among all socioeconomic levels indicate that early intervention has universal powers.

Did the intellectual benefits last? The gains remained solid after five years and appear to be holding now, some eight years later.Just as Wiesel and Hubel showed that brain cells that normally process vision won't work if they are not stimulated, Saul Schanberg of Duke and Tiffany Field of the University of Miami showed that touch is also critical to the brain.

Newborn mice separated from their mothers stop growing. The researchers found that the mothers' licking was the cue that told the pups that all was well and that they could continue their development. Without the licking the brains of the pups went into a survival mode. The absence of licking meant that the mother was not present, so there was no food. Their brains shut down the feeding response to conserve what energy the animals had. After a prolonged absence of licking, the pups failed to thrive. But the pups' feeding response could be restored when the mother resumed licking them, or when researchers stroked them with a wet artist's brush.

Knowing that premature infants who well were kept in incubators bearing "Do Not Touch" signs did not thrive, Schanberg and Field got an idea. Human babies are not licked, but they are held and their backs are rubbed.

The researchers found that touching preemies in this way affected their brains, just as it did the infant mice. Stress hormones declined, and the preemies doubled their growth rate. Thanks to this discovery, preemies are routinely held and rubbed and they develop at a more normal rate.

Even short-term babies can benefit from massage. Field studied normal-weight babies born to depressed adolescent mothers. These infants have two strikes against them---their stress hormones are churning and they receive little stimulation from their mothers. Field compared 15 minutes of massage twice a week to a similar period of rocking to determine which technique was more effective at calming these babies.

She found that massaging significantly lowered stress hormone levels in the babies, and that they cried less, gained more weight and showed greater improvement in measures of emotionality, sociability and soothability temperament. Rocking did not do much for the babies.

Once the door into the brain was opened, was only a matter of time before scientists realized they could study the biology of violence.

Researchers are finding that genes can be altered by environmental stimulation to work harder or to work less, sometimes increasing a person's risk of aggression or violence. They are also finding gene mutations that are more easily affected by environmental factors, such as alcohol and stress, making some people who have these mutations even more prone to violence.

As a society we seem to be inadvertently contributing to the increased rate of violence by what we do and what we fail to do. Among the factors that are now implicated as potential contributors to the genetic-environmental link to violence are the great increase in births to unmarried teenagers, babies born into overcrowded and impoverished environments, brain injuries, alcohol, cocaine, steroids, and lead poisoning.

As we learn how to use the brain, we are also learning how easily it can be damaged by the lack of the right kind of stimulation or too much of the wrong kind, violence.

The wonderful world of molecular biology is also revealing the brain's self-healing powers--- hormones and other chemicals that nurture and sustain brain cells. When these chemicals begin to dry up, as they sometimes do with age and with some mental disorders, brain cells wither and die.

Memory loss, Alzheimer's disease, Parkinson's, Huntington's, and other degenerative diseases of the brain are now believed to be the biological desert created when these rejuvenating chemicals vanish. If we can measure when our brain-nurturing chemicals start to decline and restore them to youthful levels, we may be able to cure or prevent many of the things that go wrong with the brain.

Among the exciting new findings:

Hormones---estrogen, progesterone, testosterone and growth hormone---play key roles in maintaining many types of brain cells. Some of these hormones, which may become the first effective drugs to prevent Alzheimer's disease and memory loss, have already produced promising preliminary results.

Estrogen, once thought to be solely a female sex hormone involved in reproduction, is turning out to be an important rejuvenator of female and male brains. A number of studies now show that women who are on estrogen replacement therapy after menopause have a dramatically lower risk of developing Alzheimer's, in addition to their greatly reduced risk of heart disease and osteoporosis.

Drugs are improving learning and memory in animals and some of them are being tested in humans. In one study at Northwestern University Medical School, researchers are testing a drug that boosts memory in normal older adults by 50 percent as measured on a test.

Brain chemicals called neurotrophic factors keep cells healthy and communicating with each other. When these factors diminish or disappear, the brain cells they nourish shrivel up. Prodded by the National Institutes of Health, scientists are gearing up to test one of them, nerve growth factor, to determine if it can stop the destruction caused by Alzheimer' s disease. Other neurotrophic factors may make it possible to grow new brain cells to replace missing ones.

Is there a bottom line to this new research? Most certainly.

The amazing discovery of the brain's plasticity---its ability to physically rewire itself to become smarter---makes mental stimulation, in the long run, more essential to the body than food. That the brain thrives with good nourishment is a concept that has profound significance for individual achievement and for the way parents raise their children.

The brain's food is education. Just as the food we eat gives our immune systems the strength to fight off life-threatening infectious germs, education protects us against bad choices. In effect, education acts like a vaccine that boosts our mental powers, making us more resistant to illness and premature aging.

Education provides such strong immunity, in fact, that people who acquire more of it are living longer than ever before while those who don't have it are falling farther behind. It is the secret to a healthier, longer life.

For people who don't grab at the opportunity for education, the news is grim. They are on the wrong end of a widening gap between people who build more brain power and those who ignore it, and they are more likely to die younger.

Despite an overall decline in death rates in the U.S. since 1960, poorly educated low income white males die at rates that are three to seven times higher than white men with better education or higher income, Dr. Gregory Pappas of the National Center for Health Statistics found in a 1993 study.

The earlier education is acquired, the more impact it has against sickness and early death. Education throughout life acts like a continuing series of booster shots.

Education works in two fundamental ways:

Biologically, by laying down significantly more connections between brain cells that accompany learning. Memory, as a result, is increased and the additional connections also provide a buffer against the destructive forces of Alzheimer's disease.

Behaviorally, by promoting positive values and attitudes about health, higher self-esteem, effective coping skills, access to preventive health services and association with people who have similar views. At the same time, education reduces risky behaviors such as smoking.

the long run, more essential to the body Just as some people fail to get vaccinated against common childhood infections, others fail to take advantage of the immunizing effects of education. Half of all high school students in Chicago and some other large cities, for instance, fail to graduate.

The toll this takes on the brain is staggering. Children born to mothers who have less than 12 years of education have a fourfold increased risk of mental retardation, said Dr. Marshalyn Yeargin-Allsop, a medical epidemiologist at the CDC's Division of Birth Defects and Developmental Disabilities.

"This regardless of race," she said. "White children had the same fourfold risk as black children if their mothers didn't complete high school."

A CDC study of more than 1,000 children showed that mild retardation, defined as having an IQ between 5O and 70, occurs at the rate of nearly one in 100 children. The biggest risk factor for mild retardation is the mother's low educational level, which far exceeds the risk posed by poverty.

About 22 percent of all births in this country are to mothers with less than a high school education, Yeargin-Allsop said. These women often do not know how to provide stimulation---such as talk, toys, and physical activity---to their infants, which can lead to stunting of the brain during the crucial first three years of life, she explained.

Mild mental retardation is generally believed to be caused by a failure to provide the brain with the kinds of experiences from its surrounding world that it needs to develop to its maximum capacity. Early educational intervention programs for children at-risk have shown that they can increase IQ levels by 15 points or more.

"At least half of the cases of mild mental retardation are preventable," Yeargin-Allsop said. "We can leapfrog over the risks if young people stay in school and get as much education as they can."

If early education is like a vaccine against risk factors, then giving it to poor, deprived children should help protect them as they grow older. That's what David Weikart, president of the groundbreaking High-Scope Perry Preschool Study in Ypsilanti, Mich., set out to prove in the late 60s.

Weikart randomly divided 127 African American children ages 3 and 4 into two groups. The children were born in poverty and had a high risk of failing in school. One group received intensive preschool education 2.5 hours a day for 3.0 weeks. The other group served as controls.

"The educational program focused on getting kids to make choices between things that might either be good or bad for them and to invent solutions to the problems they were working on," he said.

Now, 27 years later, the children who were in the intervention program are doing significantly better as adults than the controls. Seventy-one percent of them finished high school compared to 54 percent of the controls.

And they have less risky lifestyles. The children who were in the education program have less than one-third the risk of being arrested for drugs as the controls, and girls in the program are one-third less likely to have babies out-of-wedlock than their peers in the control group. Those in the program are less likely to have been on welfare and more likely to own their own homes, have good jobs and be in a stable marriage.

Society benefits too. For every dollar initially spent on educating the children in the intervention group, the public is receiving $7.16 in savings from reduced crime, reduced welfare, reduced cost of education and more tax payment on earnings.

The evidence continues to grow that low IQ levels are preventable in many children if they are. given the right help early in their lives.