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Most educators and parents know, without the aid of science, how volatile teenagers can be: placid one moment, a stick of dynamite the next. But a recent book by a psychologist鈥攁nd former high school teacher and school counselor鈥攖akes the conclusions from scientific studies of the adolescent brain and turns them into practical advice.

David Walsh, the author of WHY Do They Act That Way?: A Survival Guide to the Adolescent Brain for You and Your Teen, said he began reading in the mid-1990s about studies of the brains of teenagers based on scans with magnetic resonance imaging.

鈥淚t started to make so much sense in terms of so many things I鈥檝e learned from a psychological point of view,鈥� said Mr. Walsh, who is the founder and president of the National Institute on Media and the Family, a nonprofit organization based in Minneapolis that examines the impact of electronic media on families.

Pioneering research on normal adolescents, led by scientists at the National Institutes of Health, has proved that the adolescent brain is not a finished product, but a work in progress, according to Mr. Walsh. That is contrary to the conventional wisdom that the crucial connections between neurons, or brain cells, are forged in early childhood, and that hormones are the root cause of teenage volatility.

鈥楶ower Struggles鈥�

Dynamic changes take place in the brain at roughly the time of puberty, Mr. Walsh says, drawing particular attention to the prefrontal cortex, just behind the bone of the forehead.

The prefrontal cortex is 鈥渟o key to understanding adolescents,鈥� he writes in his book. 鈥淚t plays the role of the brain鈥檚 executive or CEO and is responsible for planning ahead, considering consequences, and managing emotional impulses. It is also called the brain鈥檚 conscience.鈥�

As the brain forges new circuits involving the prefrontal cortex and lets other circuits 鈥渨ither and die,鈥� many adolescents show dramatic changes in personality, notably in their impulse control, he suggests.

鈥淎n adult prefrontal cortex would say, 鈥業鈥檇 better watch what I say,鈥� but an adolescent鈥檚 [prefrontal cortex] can short-circuit and he or she may mouth off, sometimes leading to unpleasant consequences,鈥� he writes in the book, which was published in 2004 by the Free Press, based in New York City.

Such changes, at their worst, can create crises in families and discipline problems in schools.

鈥淭he fact is that the teenage brain is built for power struggles,鈥� Mr. Walsh said in an interview. 鈥淪o what you don鈥檛 want to do is get into power struggles, but you don鈥檛 want to be a doormat either.鈥�

Although Mr. Walsh cites the work of some of the nation鈥檚 most eminent brain researchers, some researchers question the validity of turning brain research into practical lessons in handling teenage behavior.

Researchers React

鈥淎dvice to parents and educators at the present time should really not be based on findings in neuroscience鈥攚e鈥檙e not ready for that yet,鈥� said Dr. Daniel S. Pine, a neuroscientist in the mood- and anxiety-disorders program at the National Institute of Mental Health in Bethesda, Md.

鈥淭he relationship between behavioral changes in adolescents and changes in brain structure and function is highly complex,鈥� Dr. Pine said. 鈥淲e have too limited an understanding about the relationship between changes in behavior and changes in brain structure and function to draw conclusions about how those are related.鈥�

As one gauge of the limits of the research, Dr. Pine notes that even today, brain conditions such as bipolar disorder are still diagnosed using checklists of behaviors, not MRI brain scans.

Mr. Walsh conceded that he is pushing beyond the research. But he believes he is consistent with it, not 鈥渟peculative.鈥�

Dr. Ronald E. Dahl, a pediatrician in the department of psychiatry at the Western Psychiatric Institute and Clinic at the University of Pittsburgh, generally agrees with Dr. Pine that it鈥檚 too early to cite science as the source of advice for educators and parents because so many factors influence adolescents鈥� emotions.

Regulating Emotions

But Dr. Dahl said the research supports the conclusion that educators and parents need to monitor teenagers鈥� behavior. 鈥淚t鈥檚 a fine line,鈥� he said. 鈥淜ids need to have freedom to develop self-regulatory skills, but they also need a lot of monitoring to keep them safe while they鈥檙e experimenting with their self-regulation.鈥�

He pointed out that the refinement of the self-regulation process can have far-reaching effects for teenagers. For example, he said, the development of teenagers鈥� 鈥渃ircadian system鈥濃�攖he biological clock in the brain that influences sleep, body temperature, and hormones鈥攇ives them a 鈥渟light tendency to be more owl-like.鈥�

That tendency does not by itself make teenagers stay up later, he said. But throw in other factors鈥攕uch as teenagers鈥� elevated appetites, their greater freedom in choosing their own bedtimes, and a cultural tendency to stay up later鈥攁nd the result may be students who are especially grumpy or temperamental in classes.

鈥淲ith modern forms of entertainment exciting them, and exciting things to do [later at night], it spirals,鈥� Dr. Dahl said. 鈥淏ut only a tiny amount of this is really biological.鈥�