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Shankar Vedantam Washington Post Staff
Writer
June 3, 2001; Page A1
Neuroscientist Jay Giedd was studying the brains of healthy teenagers when he noticed something odd: The brains appeared to change in unexpected ways as the youths matured through adolescence.
When Giedd looked closer, the National Institute of Mental Health researcher realized that the most dramatic shifts around puberty occurred in the front of the brain, in an area believed crucial for advanced mental functions such as reasoning, making judgments and self-control.
Could the alterations account for the impulsive, erratic and sometimes irresponsible behavior often seen in teenagers?
"Some kids are more likely to take risks than adults, and those are the areas that are undergoing drastic changes," said Paul Thompson, a mathematician and neurologist at the University of California at Los Angeles who helped Giedd produce striking images of changes in healthy teenagers' brains. "It mirrors cognitive changes."
Giedd and Thompson's work is part of a growing body of scientific evidence suggesting that rebelliousness and other stereotypical teenage behaviors commonly blamed on raging hormones may be partly caused by a burst of rapid change sculpting the developing teenage brain.
The theory is speculative. But if it turns out to be true, it would underscore the importance of guiding children carefully through adolescence, because the right kinds of teenage experiences might build the structures and connections necessary for a healthy adulthood.
"If the teens are doing music and sports and academics, that's how brains will be hard-wired. If they are doing video games and MTV and lying on the couch, that would be how they are hard-wired," Giedd said. "Teens are most likely to experiment with drugs and alcohol. I often show teens my data curve [and say], 'If you do this tonight, you may not be affecting your brains just this weekend but for the next 80 years of your life.' "
The theory is controversial because the roots of behavior are complex and cannot be easily explained by relatively superficial changes in the brain. Critics say the theory reduces the range of teenage behavior to stereotypes.
"The idea that because the frontal portions of the brain are immature and therefore children undertake risky behavior is nonsense," said John Bruer, president of the James S. McDonnell Foundation in St. Louis, which funds research in cognitive neuroscience.
"What you have is folk theory about irresponsible, careless adolescents who are annoying around the house, and people are making up these stories to say behaviors can be rationalized by looking at fine brain structure," Bruer said. "The tendency here is to take our folk ideas and theories and prejudices about what adolescent behavior should and shouldn't be and make some biological explanation for that."
Giedd agreed that what scientists know for sure is limited, but he added that the findings are intriguing. "The solid data is the gray matter thickens, peaks around puberty and thins. The rest is pretty much speculation. There are very few things that we can say beyond that. I don't mean to say that video games destroy the brain -- the real answer is we don't really know."
Scientists have struggled for hundreds of years to figure out how brain changes affect behavior and which parts of the brain are responsible for specific mental abilities. Until recently, all scientists could do was study patients with brain injury to see how the damaged areas affected behavior. They also examined the brains of people who had died to look for unusual features that might explain the person's behavior.
A confounding factor in such studies is that the brain can frequently compensate for damage by rerouting wiring to healthy areas. In that sense, the image of the brain as having interlocking Lego blocks that perform different functions -- the model of the pseudoscience phrenology -- simply doesn't work.
But in recent years, advances in brain scan technology have allowed researchers to evaluate which parts of the brain use energy while performing certain tasks and which parts vary in their water content, which distinguishes different types of tissue. Researchers ask patients to perform mental tasks while being scanned to get a snapshot of the brain in action. Such tests have suggested links between behavior and performance and various brain structures.
"The more mature an individual's frontal lobe appeared, the better they performed on the verbal test," said Elizabeth Sowell, an assistant professor of neurology at the University of California at Los Angeles. "You can take 10 8-year-olds, and there is a range of performance. We are finding that the structure of the brain helps predict that variance."
Brain scans of healthy children show that the amount of gray matter, which consists of neurons and the connections between them, and the amount of white matter, the insulation wrapped around nerve fibers, fluctuate from birth onward, possibly because the brain is learning.
Gray matter actually reaches a peak while the fetus is in the second trimester, then begins to shrink and continues to shrink after birth. The shrinking of gray matter is one way the brain translates experience into knowledge. As babies learn to see and hear, scientists believe the brain lays down wiring by eliminating neurons that are unnecessary. White matter slowly begins to grow as the brain wraps its finished wiring, improving the efficiency of nerve signal transmissions.
Then there is a switch, and gray matter starts to increase by about age 3 or 4, Giedd said. The increase continues until around puberty, when researchers such as Giedd recently noted there is another rapid decline -- especially in the frontal areas of the brain.
"If you slap your forehead -- it's right above the eyes," said Jordan Grafman, a cognitive neuroscientist at the National Institute for Neurological Disorders and Stroke. "It goes back to about in front of the ears. People refer to it as the prefrontal cortex or the frontal lobe. The prefrontal cortex does reasoning, planning, social behavior and knowledge -- the ability to infer the mental states of others, to have insight and reflect on your own behavior -- all the kinds of things you want to teach teenagers."
Based on data from living patients and autopsies, researchers have linked the frontal areas of the brain with judgment and self-control, which has led to the speculation that the distinctive changes in teenage brains are linked with typical adolescent behaviors.
Although there isn't definite proof, Sowell said, "we feel pretty strongly that there is a link."
In animal studies, said Bill Greenough, a psychologist and neuroscientist at the University of Illinois, scientists have demonstrated the powerful connection between the brain and behavior by altering the brains of animals and studying their behavior, or by drastically altering their environments and behavior and seeing the consequence on their brains.
But that research doesn't necessarily neatly translate to humans, because the behavior that most people are interested in about adolescents -- that "Keep Out" sign on the door or early experimentation with sex -- are relatively subtle behavioral changes and purely human concerns.
Definitively linking brain change with behavior might require an understanding of the complexity of inter-neural connections, which is probably where the chemistry of the brain becomes thought, ideas -- and behavior. But technology isn't there yet, which is why brain images cannot tell the difference between people with IQs of 80 and 160.
"There's a gross misunderstanding on the part of the general public about how much recent brain work is ready for prime time in terms of applications to education and social service programs," said Jack Shonkoff, a pediatrician at Brandeis University and chairman of a panel at the National Research Council that studied how brain research could be translated into public policy.
"It doesn't tell us anything different that would lead to different clinical practices, public policies, educational strategies," he said. "Brain research doesn't lead us to be smarter at how we teach kids."
Bruer, author of "The Myth of the First Three Years," a book that criticized hype over research on early child brain development, noted that the sudden interest in teenage brains replaced an earlier fascination with the brains of infants, which triggered a wave of product marketing. Anxious parents, for example, were told that playing Mozart to babies worked miracles on the brain -- a theory that was subsequently seriously questioned.
"We don't have any magic manipulation so that if we do X to the brain, we stop having problems with adolescents," said Linda Patia Spear, professor and chairman of the department of psychology at the State University of New York in Binghamton who has studied how brain changes and hormones affect teenage behavior. "If anything is said like that, it will be like Mozart and babies. It's oversimplified. When you are talking of billions and billions of connections in the brain, any simple solution is unlikely to be meaningful."