Miracle grow

The teen brain is a marvel of smarts. It’s just not all filled in (yet).

Dr. Frances Jensen, here at Lexington High, gives teens and parents the facts about adolescent neurology. Dr. Frances Jensen, here at Lexington High, gives teens and parents the facts about adolescent neurology. (Gretchen Ertl for The Boston Globe)
By Elizabeth Cooney
June 28, 2010

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Adam Davis says one of his brightest friends makes the most ridiculous mistakes. For all his smarts, he’ll cross the street without looking.

More scary is the stuff he hears from other friends.

“I know some people who are heavy drinkers, and they’ve actually told me they feel their memory is going. They drink and then they black out, more and more,’’ said Davis, a 20-year-old Lexington High graduate who attends Occidental College in Los Angeles. “They don’t change their behavior. I don’t think it’s addiction. I guess that gets into judgment.’’

Smart kids doing stupid things: It’s the teen brain paradox. Extraordinarily quick to learn and rapidly reaching fluency in abstract thought, teens still make bonehead decisions, perhaps more so when routines relax in summer. But that’s because they’re operating with brains that are still a work in progress.

Of all the organs in our bodies, the brain takes the longest to develop. Frontal lobes — the seat of judgment — are the last pieces to be fully connected to the parts of the brain that sense danger or solve calculus problems. A growing body of neuroscientific evidence places full brain maturity at about age 25, well past the point when young people begin to drive, drink, vote, or go off to war.

“We all know what the frontal lobe does,’’ said Dr. Frances Jensen, a neurologist at Harvard Medical School and Children’s Hospital Boston. “It’s insight, judgment, inhibition, self-awareness, cause and effect, acknowledgment of cause and effect. And big surprise: It’s not done in your teen years. Hence [teens’] impulsiveness, their unpredictable behavior, their lack of ability to acknowledge and see cause and effect, despite the fact they are getting 800s on their SATs and can be cognitively highly functional and memorize at a much more impressive rate than we as adults do later.’’

Doctors, developmental psychologists, and educators say the brain development message gains urgency as more is learned about the teen brain, a neglected area of research in Jensen’s view. The very qualities that make learning easier in youth also make habits like smoking or drinking more deeply embedded, for example. Then there are differences in brain chemistry that mean antidepressants may act differently on young brains, notably increasing suicidal thoughts in enough cases to warrant a warning from government regulators. While youth is a time of resilience in many ways, it’s a myth that people can make up for damage later when it comes to the brain, Jensen said.

“You’re actually more sensitive, more vulnerable’’ before adulthood, she said.

Jensen has been spreading this message with the zeal of an evangelist. A specialist in age-specific brain injury with a particular focus on epilepsy in newborns, she began exploring adolescent neurology when her two teenage sons baffled her with their bizarre behavior.

“It was like living with this alien species,’’ she recalled. “There was so much I didn’t get.’’

The answer to the paradox is gray and white, neurologically speaking. Gray matter includes brain cells that from birth begin to connect to one another, forming synapses in the small space between two nerve cells where electrical signals travel via chemical transmitters. These connections made during development are also what we use to learn and remember. In order to make new connections between different brain cell groups, cells on both sides have to be “on,’’ or in a state called excitation. Its opposite is inhibition, and in adults the two are balanced. But in the brains of babies, children, and to a lesser extent teenagers, excitation is higher. They’re juiced for connections, Jensen said, making learning almost effortless for a child.

White matter lies below the synapse-making gray matter. Its job is to conduct the signals sent between cells as fast as possible via a fatty substance called myelin. Myelin is nature’s insulation, but it builds slowly, into mid-adulthood.

The brainstem, which controls breathing, for example, has its synapses connected and its myelin insulation in place at birth. By mid-childhood, other parts of the brain are connected and myelinated, too, but those frontal lobes are the last to be completed. The impressive learning ability is there, thanks to levels of excitation higher than in adult brains, but the myelination that would bring judgment into play before crossing the street or deciding to binge drink again isn’t all there yet. Teens just can’t access their frontal lobes as quickly as adults.

Drinking and drugs act potently on the teenage brain, neuroscientists now believe, because addiction itself is a form of learning that banks on better memory formation.

“Teenagers get more robustly addicted and for a longer time,’’ Jensen said. “Things like pot have a longer effect on these teen brains because they have more machinery for those molecules to be connected.’’

When Jensen speaks to high school students, often the day after lecturing to their parents, she gets their attention when she tells them the marijuana they smoke over the weekend will still impair them on a test they take the following Thursday. She firmly believes in appealing to the intellectual side of her young audiences, so she presents annotated slides and cross-sectional views of the brain, just as she would for a scientific meeting.

“Instead of sitting there saying ‘Don’t do that,’ we give them facts,’’ she said. She tells them, “This isn’t a myth, this isn’t a bunch of adults wagging their fingers at you. This is data and please consider this. I know you have brain cells up there. And you do better at understanding my slides than your parents.’’

After Jensen presented a talk attended mostly by Lexington High School parents last month, English teacher Karen Russell said the teen paradox is familiar to her from what she sees in the classroom and as a parent. Sophisticated in their thinking, her students follow where she leads them intellectually. But decision-making is inconsistent.

“It’s kind of like a learning disorder. They’re so strong in one area and weak in another,’’ she said.

She tries to give her students a scaffolding for good decision-making, but she worries about them once they hit college, where the norms are different, especially outside the classroom. “Grades don’t even come home when they’re in college,’’ she said. “These kids need more support and monitoring.’’

Julie Fenn, a prevention specialist for all the Lexington public schools and a health teacher in the high school, presents the story of brain development to students as part of the curriculum, but cites national surveys of youth risk behavior showing that parents are the biggest influence on the decisions young people make.

“I really want parents to understand they are all good kids,’’ she said. “It’s not about being good or bad. It’s about recognizing what the limitations are and looking at the physiological piece in terms of brain development and knowing that they are going to have to supervise and monitor kids and instill their values.’’

Like brain development, the job doesn’t end with high school graduation, according to Maryanne Wolf. A developmental psychologist at Tufts University who until recently joined Jensen on community lectures, she calls such continued oversight one of the last, great responsibilities for parents as their children become independent.

One window she sees opening in the college freshmen and sophomores she teaches is metacognition, or thinking about thinking. Stepping outside themselves, they consider how others think and in so doing, they can stretch to learn autonomy of thought.

“Their judgment is outdistanced by their cognitive development. Studying it helps with the development of judgment,’’ Wolf said. “We can help place them on their own trajectory of development.’’

Jensen has a sobering message for students, and their teachers, and parents.

“You have this amazingly valuable organ up there. You only get one,’’ she said. “Take good care of it.’’

Elizabeth Cooney can be reached at

What's a parent to do?

■ Be tolerant. Your teenage children are not trying to be jerks.

■ Cut down on the stress in their lives. It’s not an easy stage of life for them, either.

■ Make sure they’re not sleep-deprived. That amps up stress hormones.

■ Talk to your children.

Teen schemes

■ Count to 10 before you rush into anything.

■ Ask a friend for advice before you make a decision.

■ Keep in mind that drugs and alcohol can cause your developing brain to take an extra-hard hit.

■ Talk to your parents.

SOURCE: Dr. Frances Jensen