(FORTUNE Magazine) – WHEN HIS PARENTS brought 3-month-old Jacob Stark to UCLA's medical school last winter, he was stricken with infantile spasms, a pernicious form of epilepsy that starts at birth. Dozens of times a day, seizures wracked his body. The disease makes it impossible for an infant to grow properly, and until recently Jacob's prospects would have been grim: confinement to bed, sedation to a near-vegetable state, and early death. But scientists at UCLA have pioneered a dramatic treatment that relies on a new understanding of the adaptability of the brain. Using a high-tech scanner that translates the brain's metabolic workings into vivid color images, they were able to pinpoint the source of the seizures: renegade neurons in the left temporal and occipital lobes, above and behind Jacob's ear. That information made it feasible to undertake surgery that few neurologists would have risked five years ago. In a five-hour operation, Dr. Warwick Peacock eliminated the offending neurons -- by cutting out a fifth of Jacob's brain. According to traditional neurological theory, Jacob should have emerged crippled, perhaps paralyzed on one side of his body, unable to think logically or speak -- skills long thought to depend on the brain's left side. Instead, a startling recovery: Within weeks of the operation, the rest of Jacob's brain took over the function of the missing part. Today he is a normal 1-year-old -- able to stand, play, and delight his parents. His only handicap is a loss of peripheral vision in his right eye, which the missing part of his brain controlled. Apart from that, in medical terms he suffers ''zero deficit'' in function, intelligence, and emotion. In human terms, as his mother says, ''Jacob is doing all the things they told us he probably would never do.'' The cure of Jacob's epilepsy is a harbinger of huge advances in neuroscience and the treatment of brain disorders. By the time Jacob enters fifth grade in the year 2000, doctors may be able to restore the use of limbs paralyzed by strokes, enhance memories ravaged by Alzheimer's disease, and treat other forms of mental illness with an effectiveness unheard of today. Brain research will also advance mankind's understanding of mental health, and of the mind's most noble functions -- the ability to conceptualize and to create poetry and music. The consensus among thousands of U.S. scientists: The time has come for a major, wide-ranging assault on the mysteries of the brain. The research battalions are on hand. When the Society for Neuroscience held its first meeting 19 years ago, 1,500 attended; some 15,000 turned up for the annual conference in St. Louis this November. Many of the scientists were from the pharmaceutical industry, which sees enormous potential in exotic new brain drugs. At least 20 small neuroscience companies have organized in recent years, while many established pharmaceutical houses have greatly expanded their brain research, turning neuroscience into the fastest-growing segment of biotechnology (see box). The scientists are attracted by the immensity of the challenge. Though the brain is sometimes compared to a computer, it is unimaginably more advanced. A single neuron, or nerve cell, may maintain a million communication links with its neighbors. If a computer were built to replicate the brain's network, it would occupy a ten-story building covering the entire state of Texas. Arnold Scheibel, acting director of the Brain Research Institute at UCLA, calls the & brain ''a cosmic, celestial organ.'' On his desk he keeps a black and white photograph of the Andromeda galaxy, which comprises some 100 billion stars, as many as there are cells in the brain. Says Robert C. Collins, chairman of the neurology department at UCLA: ''The brain represents the furthest extent of biological evolution.''

For all its sophistication, the brain falls prey to a terrifying array of diseases. According to the Society for Neuroscience, located in Washington, D.C., fully one-sixth of the U.S. population -- 48 million people -- suffer from brain disorders. These range from such handicaps as speech defects (eight million) and deafness (two million) to afflictions like stroke and epilepsy (two million each). As the population ages, more and more people will become susceptible to Alzheimer's and Parkinson's diseases. For reasons science can't yet explain, depression and other forms of mental illness are hitting Americans at younger ages than ever before. Still another fast-growing group of the mentally ill: sufferers from AIDS-related dementia. The estimated annual cost of medical care for all these afflictions is at least $400 billion. AS RECENTLY as 1970, brain research was the province of an avant-garde. Armed only with microscopes and other traditional gear, a few scientists groped for knowledge, dissecting the nervous systems of worms, planting electrodes in cats' brains, devising treatments for humans with drugs whose actions were only dimly understood. Even so, science made remarkable advances. The discovery of the drug L-dopa in the late 1960s, for example, made it possible to reverse, at least temporarily, the tremors associated with Parkinson's disease. But the brain's inner workings remained hidden. No more. Sophisticated tools, made possible by the explosive growth of computing and biochemistry, are opening new windows on the brain. In hospitals around the country, doctors are using magnetic resonance imaging, or MRI, to generate stunning pictures of the living brain's anatomy. At Barrow Neurological Institute in Phoenix, Arizona, Burton Drayer, a physician, has adapted MRI to study the possible connection between the accumulation of iron in the brain and aging; MRI is helping reveal structural abnormalities in the brains of schizophrenics, autistic children, and manic-depressives. Meanwhile, Christopher Gallen, a neurologist at the Scripps Clinic in LaJolla, California, is using another new technique, magnetoencephalography, or MEG, to unlock the secrets of how the brain makes sense of what the body sees, hears, smells, tastes, or touches. His focus is the cerebral cortex, a table-napkin-thin layer of cells on the brain's surface. Sometimes called the ''superbrain,'' it elevates mammals over the lower forms of life. MEG works by recording the faint, fleeting magnetic fields generated by the cortex's electrical activity. Investigating the part of the cortex that handles signals from the ears, Gallen and others have shown it to be organized in squads of cells, each sensitive to a different frequency. Even the venerable electroencephalograph, or EEG, is contributing to new brain research. The device uses electrodes on the scalp to graph the brain's electrical activity. E. Roy John, head of the brain research lab at New York University's medical center, has devised a computer-enhanced EEG system that compares a patient's results with thousands of previous cases stored in its database and produces color images instead of graphs. The device helps psychiatrists at many U.S. hospitals evaluate complex cases of schizophrenia or depression in patients. The most potent imaging tool in neuroscience's new high-tech arsenal is positron emission tomography, or PET, the type of scanner UCLA doctors used to identify baby Jacob's epileptic tissue. Developed in the early 1970s, PET is the invention of Michael E. Phelps, a UCLA physicist, mathematician, and chemist, and his colleague, physicist Edward Hoffman. Phelps grew up in working-class Port Orchard, Washington, and spent ten years as an amateur boxer before deciding to try to heal brains rather than knock them senseless. In a typical PET procedure, doctors inject a radioactive isotope into the patient's blood. It attaches itself to molecules of glucose, the brain's fuel. As the blood circulates, neurons take up the glucose and consume it; the higher the activity, the greater the concentration of glucose and the isotopes it carries. A ring of crystal detectors records the temporary buildup of radiation in these hot spots. The radioactivity quickly dies out, but the stored data can generate colored cross-sections of brain activity. THESE SNAPSHOTS are astonishingly revealing. Phelps can show, for example, that a listener's training determines where in the brain music is processed. When a trained musician listens analytically, a PET scan shows a spot in the left hemisphere that lights up. When an untrained listener responds emotionally, by contrast, a spot in the right hemisphere grows brighter on the scan. In most people, the left hemisphere is the seat of analytical reasoning while the right hemisphere handles emotions. A PET scan literally can trace thoughts as they occur. Consider the word test devised by neurologist Marcus Raichle of Washington University in St. Louis. It involves showing a succession of TV images to a volunteer and producing a snapshot of the brain as each image is flashed. The first, which has arbitrary lines on it, triggers a diffuse response. The second, with a random string of consonants, gets a response only slightly less diffuse. But the third image, of a pseudoword such as TWEAL, causes a blaze of activity in several spots as the brain decides whether it is seeing English or nonsense. The fourth image, of a real word such as BOARD, causes just one area to flare as the brain gets the idea -- almost like the proverbial light bulb going on. Eventually, Raichle hopes to apply the technique to treat dyslexia, other learning disabilities, and the devastating damage to speech that sometimes occurs in strokes. UCLA psychiatrist Lewis Baxter uses PET to study the effects of cocaine. The drug is thought to cause euphoria by boosting the level of dopamine, an essential brain chemical. A dramatic set of PET images shows the aftermath of cocaine abuse: Days after a dose, dopamine-related activity is severely reduced; the patient craves food and feels sleepy and depressed. Weeks may pass before brain activity returns to near normal. At St. Elizabeth's Hospital in Washington, D.C., neurologist Daniel Weinberger has begun to apply a version of PET to the treatment of mental patients. He uses the scanner to see whether an experimental drug has corrected aberrant activity in their brains. Says Weinberger: ''We're no longer looking at some rat model. Instead, we see if a medication actually reverses something in the scans.'' At $5 million per installation, PET technology is prohibitively expensive for ordinary hospitals. But it holds such promise for the treatment of mental illness that the National Institute of Mental Health (NIMH) is paying for the construction of imaging centers around the U.S. Neuroscientists are rapidly closing in on the secrets of how the brain functions. By applying methods from molecular biology, they are charting an interplay of chemistry and electricity far more complex than anyone imagined a few years ago. In decades past, debate among brain scientists revolved around the issue of ''soups'' (chemistry), vs. ''sparks'' (electricity). The sparks camp held ascendancy for a long time. Scientists thought the brain worked primarily by speeding electrical signals along axons, the transmission trunks of nerve cells. Arriving at synapses, tiny slits that separate neurons, the signals set off the release of chemicals known as neurotransmitters, such as dopamine. These cross the synaptic gaps and cause neighboring neurons to re- create the electrical message and pass it along. Repeated thousands of times a second, this relay process can help trigger the continuation of a thought, the blink of an eye, the throwing of a ball. BUT NOW IT turns out that the brain is less a sparks switchboard than a soups kitchen. Brain chemicals have been discovered that exert their influence by bathing whole systems of neurons. Such chemicals are called neuropeptides; several dozen are known today, but there may actually be thousands. Their billions of possible combinations and permutations is what now appears to allow nuances of thought, mood, and emotion. Says Nobel laureate Julius Axelrod of NIMH: ''The brain's electrochemical language is as rich and subtle as that of Shakespeare. And we are just beginning to learn our ABCs.'' So delicate are the balances of such chemicals that a shortage or a surfeit of a single substance can lead to emotional or behavioral disturbance. Solomon Snyder, chief of neuroscience at Johns Hopkins University medical school in Baltimore, predicts that as researchers understand better how brain chemicals interact, they will be able to tailor drugs to precise subcategories of mental illness. For example, he says, a pill will someday exist to treat wallflower syndrome, a paralyzing shyness that prevents a person from living a normal life.

PERHAPS the most stunning breakthrough of the new brain research involves plasticity, the brain's remarkable ability to adapt its biochemical circuits in response to experience or injury. Plasticity has long been taken for granted as an attribute of childhood. Scientists use it to explain why children learn quickly. But now there is evidence that the brain rearranges itself and forges new connections throughout adulthood, up to the last day of life. UCLA's Scheibel calls plasticity in the mature brain ''the most dramatic single thing we're now learning.'' Adds Floyd E. Bloom of the Scripps Clinic in LaJolla, California: ''This is something we didn't believe as recently as five years ago.'' Physical therapists have long suspected the presence of such a mechanism in victims of head injury and strokes. In an up-to-date treatment center, such as New York University's Rusk Institute of Rehabilitation Medicine, astonishing recoveries are common. Even if the cerebral circuits for, say, lifting an arm have been destroyed, a skilled therapist can often help the paralyzed limb to revive. Says Dr. Owen Kieran, director of the institute's head-trauma program: ''We often do very well with major injuries, though we have little knowledge of why the treatments work. You see actual motor changes, real changes in speech, changes in understanding. It is not just that the patients are trying hard. They have clinically observable changes.'' Like many therapists, Kieran believes that the brain reprograms healthy neurons to replace the ruined pathways. Early this year the bizarre case of the Silver Spring monkeys showed he is probably right -- and opened the possibility of a leap in the treatment of some forms of paralysis. In 1977 a Silver Spring, Maryland, scientist working for the National Institutes of Health (NIH) operated on nine macaque monkeys. In each animal he severed nerves that led from one arm to the brain, causing the arm to lose its sense of touch so that the monkey stopped using it. The plan was to wait one year and then operate on the monkeys to see how they had compensated for the injury. But before that surgery could be done, animal rights activists accused the contractor of failing to provide humane quarters for the animals. The monkeys ended up in the custody of local police, who sent them back to the NIH for safekeeping as lawsuits worked their way through the courts. When neurologists finally regained access to the animals this year, they were astonished at what they found. Though the monkeys had not relearned the use of their arms, the neurons that had been responsible for the arm's tactile sense had found other work making the monkeys' faces more sensitive than usual to touch. This odd result was revolutionary, because it proved that neurons of a mature brain can reprogram themselves. Explains NIH neurobiologist Timothy Pons, who worked on the monkeys: ''The fact that the brain is capable of that kind of reorganization implies that we may someday be able to operate on or send drugs into the brain % of a human stroke victim that will open new territory of the cortex and bring a paralyzed limb back to life.'' Scientists believe this new understanding of the brain's plasticity has far- reaching implications for the healthy as well as the sick. UCLA's Scheibel suggests it may help solve the practical challenge of retraining older workers to do new jobs. His colleague Robert Collins thinks neuroscience will exert a profound influence on all education. He predicts that one-dimensional measures of intelligence, such as IQ tests, will give way to a richer understanding of human capability, and looks forward to the emergence of educational methods that will tap an almost limitless ability to learn. Says Collins: ''The brain is so malleable that there are virtually no inherent constraints. That's where the focus belongs in a civilized society. That's where the future lies.''