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Adolescence: A Time of Vulnerability and Opportunity

Scientists and doctors now have a better sense of how the adolescent brain develops and offer guidance on how we can support young people during this often-vulnerable period.

Published November 1, 2003

By Rosemarie Foster
Academy Contributor

The two young teens meet at a dance, and in an instant are mutually enraptured. They declare their love for each other, and over the next several days think of nothing or no one else. The idea of being apart is worse than death – an untimely fate that befalls them both.

The tale of Romeo and Juliet actually predates Shakespeare’s 16th century play by several centuries, illustrating that the emotionally charged nature of adolescence is not new. Along with the traditional throes of puberty, today’s adolescents juggle more homework, tightly scheduled after-school hours, a barrage of media messages, and the temptations of smoking and alcohol.

It’s no wonder that the adolescent years – the transition between childhood and adulthood – can be the most sensitive time in a person’s life. Indeed, although physical strength and reaction times peak in these years, morbidity and mortality increase by 300% in this group.

In September, 31experts gathered in New York City to address the changes and challenges of adolescence at a meeting called Adolescent Brain Development: Vulnerabilities and Opportunities. The conference was hosted by The New York Academy of Sciences (the Academy) in collaboration with the Robert Wood Johnson Foundation and the Tobacco Etiology Research Network. The conference was co-sponsored by the National Institutes of Health.

Rooted in Biology

Investigators at the conference agreed that much of the behavior characterizing adolescence is rooted in biology, intermingling with environmental influences to cause teens to conflict with their parents, take more risks, and experience wide swings in emotion. A lack of synchrony between a physically mature body and a still-maturing nervous system appears to be a primary reason.

“It’s like turbo-charging an engine without a skilled driver,” explained conference organizer Ronald E. Dahl, MD, of the University of Pittsburgh Medical Center. Although adolescents reach adult levels of decision-making by age 15, they make poor decisions in real life. “Adolescents make a lot of decisions that the average 9-year-old would say was a dumb thing to do,” he added. Dahl delivered the keynote address in place of Alan I. Leshner, PhD, of the American Association for the Advancement of Science, whose travel plans were cancelled by Hurricane Isabel.

The interaction of biological changes and environmental challenges that make adolescence a time of increased vulnerability can also make it one of great opportunity. The adolescent brain is built to learn, amassing more knowledge in high school and college than at any other time. With the right balance of guidance and understanding, adolescence can be relatively smooth. And for most kids, that’s exactly the case, with the majority of teens getting through those difficult years just fine.

Taking Risks, Despite the Odds

Driving too fast. Sneaking out. Smoking and drinking. Adolescents know very well that these activities are unlawful, dangerous and unhealthy. So why do they do it?

Part of the answer may be found in brain chemistry, explained Rudolf N. Cardinal, PhD, of the University of Cambridge in the UK. His studies in rats demonstrate that low levels of the neurotransmitters dopamine and serotonin 5HT make them more impulsive, causing them to choose smaller, immediate rewards over larger, delayed rewards. In people, such impulsivity has been linked to drug addiction, personality disorders and attention deficit hyperactivity disorder.

Laurence Steinberg, PhD, of Temple University, emphasized that researchers who explore adolescent behavior must consider the context in which risk-taking behaviors are occurring. Adolescents are more likely to engage in these behaviors when they’re in groups than when they’re alone. Moreover, real-life situations are usually highly charged with emotion, unlike the hypothetical events postulated in investigational settings.

Steinberg added that adolescents’ biological sensitivity to rewards is different than in adults, prompting them to seek levels of stimulation to achieve the same feeling of pleasure. “Increased risk-taking in adolescence is normative, biologically driven and inevitable,” he concluded. Rather than trying to change this behavior, Steinberg suggested such measures as increasing the driving age, raising the price of cigarettes, and enforcing laws restricting alcohol sales.

The Images Tell All

Magnetic resonance imaging (MRI) data can illustrate the changes occurring in the adolescent brain. Jay N. Giedd, MD, of the National Institute of Mental Health, presented MR images showing that the brain’s gray matter – which governs thought, decision-making, movement and sensation – thickens during adolescence, peaking around age 11 in girls and 12 1/2 in boys before thinning down to a stable level by age 25.

Such thickening is not due to more nerve cells, but to an increase in connections between neurons. Although the brain then has more choices of pathways through which to send signals, those pathways are not necessarily faster, making some processing inefficient. White matter – which controls motor functions – increases linearly during adolescence, while the cerebellum (which governs balance) also grows in volume. Giedd contends that adolescence is therefore the most efficient time for teens to take on such motor activities as sports, drawing and instrumental music.

One of the last areas of the brain to mature is the prefrontal cortex. Beatriz Luna, PhD, of the University of Pittsburgh Medical Center, performed behavioral and functional MRI tests to explain why the different parts of the brain learn to collaborate better, and processing becomes more efficient, as adolescents age and the prefrontal cortex matures.

Hormones and Behavior

Are the behaviors we see in adolescents simply a result of “raging hormones?” Certainly that’s not the complete answer, but changes in reproductive and stress hormones can influence behavior. Hormonal changes during adolescence can also trigger depression during this time.

Elizabeth A. Young, MD, of the University of Michigan, asserted that reproductive hormonal changes that affect stress systems during puberty may sensitize girls to stressful life events. Studies show that depressed premenopausal women have a higher baseline level of the stress hormone cortisol than post-menopausal depressed women and than depressed men. The hormone estradiol has not been shown to make women more vulnerable to stress, but progesterone may exaggerate the response to stress. During puberty, changes in reproductive hormones can therefore make girls more sensitive to the effects of stress and can trigger adolescent depression, explained Young.

A Heightened Sensitivity

An elevated sensitivity to rewards is most apparent in teens’ use of cigarettes and alcohol. Some 17% of high school seniors say they smoke daily, and 57% report they’ve tried it. More than 80% have tried alcohol, with about 66% of them reporting they’ve had at least one episode of consuming more than five drinks.

Unlike adults, adolescents seem to be more sensitive to the pleasurable effects of nicotine and alcohol, and less likely to experience the adverse effects. Frances M. Leslie, PhD, of the University of California, Irvine, showed that adolescent rats are more likely to choose nicotine over a saline placebo than adult rats, a condition she attributed to an immature forebrain. George F. Koob, PhD, of The Scripps Research Institute, reiterated those findings in his investigations, adding that adolescent rats are less affected by nicotine withdrawal than adults. “This research provides insight into how and why adolescent humans are so sensitive to nicotine, and why this is such a critical period for intervention,” he concluded.

Why do some adolescents become addicted to smoking, while others quit and move on?

Robin J. Mermelstein, PhD, of the University of Illinois at Chicago, evaluated a group of teens to find out. They completed a questionnaire on a handheld computer seven times a day during a one-week period to assess their moods and activities, and data were correlated with behaviors such as smoking and drinking. She found that smokers are more likely to have friends who smoke and to feel a mood-boosting effect from smoking, while people who have never smoked are less likely to hang out with smoking friends. Moreover, those who try cigarettes but decide not to smoke are less likely to feel a mood boost from smoking.

The Impacts of Alcohol Consumption

Many teens consuming alcohol experience its benefits without its negative effects. H. Scott Swartzwelder, PhD, of Duke University Medical Center, demonstrated that ethanol causes memory deficits in adolescent rats by affecting the hippocampus, which regulates conscious memory. He also showed that alcohol impairs memory in human adolescents. Yet adolescents appear to be less susceptible to the sedative effects of alcohol, such as sleepiness, than adults. “During adolescence, it may be easier to drink the brain to an impaired state without realizing it,” Swartzwelder contended.

Alcohol-related memory impairment may be long-term and cumulative, suggested Sandra A. Brown, PhD, of the University of California, San Diego. Alcohol-dependent adolescents – those who reported starting early and drinking more than 700 times in their lives – had a 10% lower ability to retain verbal and non-verbal information than nonalcoholic controls, even after a three-week abstinence period. Functional MRI studies confirmed the memory impairment, though Brown noted that it is not yet possible to say whether the neurological differences predated the alcohol abuse or were caused by it.

Studies in macaque monkeys illustrate that alcohol also may increase impulsivity and risk-taking by lowering cerebrospinal fluid levels of serotonin 5-HIAA. J. Dee Higley, PhD, of the National Institute on Alcohol Abuse and Alcoholism, reported that monkeys with low CSF levels of this metabolite are more likely to take long, risky leaps between trees than those with normal levels. They’re also more aggressive, socially isolated, intolerant to alcohol’s toxic effects, and tend to over-consume alcohol. In addition, the environment plays a role: Monkeys reared by their peers are twice as likely to consume too much alcohol as are those raised by their mothers.

Just Let Them Sleep?

“Of all the potent insults to the adolescent brain, sleep deprivation is the most widespread,” said Ruth Benca, MD, PhD, of the University of Wisconsin. Without adequate sleep, people can experience deficits in learning, memory, attention, concentration, and psychomotor function, and get into more auto accidents.

Many a parent can recall problems in waking a slumbering adolescent for school. But research shows adolescents’ need to sleep late is biologically ingrained. Their bodies naturally want to go to sleep later at night. And because they need just over nine hours of sleep, they want to sleep in. But the demands of early school starting times and other activities prohibit that, explaining why so many of them make up for lost sleep on weekends.

Theresa M. Lee, PhD, of the University of Michigan, and Mary A. Carskadon, PhD, of Brown Medical School, both reported differences in sleep phase between adolescents and adults. “Many adolescents sleep too little, and in the wrong phase,” concluded Carskadon.

The answer may be simple: start high school later. But school bussing schedules in many towns prohibit that, where busses that take kids to high school in the early morning are later needed to transport elementary school students. A later school start also may cut into the time allotted for after-school activities. It’s not an easy problem to solve. Added David F. Dinges, PhD, of the University of Pennsylvania School of Medicine, “Until we get serious about time and sleep and school start time, it’s going to be difficult for kids.”

Getting Through Adolescence

What distinguishes which kids travel through adolescence smoothly from those who navigate a rockier path? Ann S. Masten, PhD, of the University of Minnesota, reported that those with the supervision of caring adults, good intellectual skills, a positive self-perception, and a positive social group are most likely to fare well. Strong bonds to school, spirituality, and community also help. Several participants agreed that we should not label adolescence solely as a trouble-prone period. “We need to avoid characterizing some adolescents as having ‘bad brains’ or ‘problem brains,’” said Daniel P. Keating, PhD, of the University of Toronto. “That’s too simplistic.”

“Adolescents are more vulnerable in risky situations because of the immaturity of their brains,” concluded Elizabeth Cauffman, PhD, of the University of Pittsburgh. “By explaining these changes, we have a better chance of understanding their behavior.”

Also read: Mental Health in Children and Adolescents


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