Brain Development


Video Activity: Brain Development: Adolescence features animations and illustrations of the changes that occur in the teenage brain.

Like the other parts of the body, different parts of the brain grow at different rates. Myelination and maturation occur in sequence, proceeding from the lower and inner parts of the brain to the cortex and from the back to the prefrontal cortex (Sowell et al., 2007). That means that the limbic system (site of fear, anxiety, and other intense emotions) matures before regions where planning, emotional regulation, and impulse control occur.

Furthermore, pubertal hormones target the amygdala and other crucial parts of the HPA axis directly (Romeo, 2013), but full functioning of the cortex requires maturation and experience beyond the teen years. Thus, the instinctual and emotional areas of the adolescent brain develop ahead of the reflective, analytic areas. Puberty means emotional rushes, unchecked by caution. Immediate impulses thwart long-term planning.

Brain scans confirm that emotional control, revealed by fMRI studies, is not fully developed until adulthood. During adolescence, the prefrontal cortex is limited in connections and engagement (Luna et al., 2013).

When compared with the brains of emerging adults, adolescent brains show heightened arousal in the brain’s reward centers. Teens seek excitement and pleasure, especially the social pleasure of a peer’s admiration (Galván, 2013). In fact, when others are watching, teens find it thrilling to take dramatic risks that produce social acclaim, risks they would not dare take alone (Albert et al., 2013).

FIGURE 14.5
Same People, But Not the Same Brain These brain scans are part of a longitudinal study that repeatedly compared the proportion of gray matter from childhood through adolescence. (Gray matter refers to the cell bodies of neurons, which are less prominent with age as some neurons are unused.) Gray matter is reduced as white matter increases, in part because pruning during the teen years (the last two pairs of images here) allows intellectual connections to build. As the authors of one study that included this chart explained, teenagers may “look like an adult, but cognitively they are not there yet” (K. Powell, 2006, p. 865).

Especially for Health Practitioners How might you encourage adolescents to seek treatment for STIs?

Many adolescents are intensely concerned about privacy and fearful of adult interference. This means your first task is to convince the teenagers that you are nonjudgmental and that everything is confidential.

The fact that the frontal lobes are the last to mature may explain something that has long bewildered adults: Especially when they are with their friends, many adolescents seek the thrill of new experiences and sensations, forgetting the caution that their parents have tried to instill. The following is one example.

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a case to study

“What Were You Thinking?”

Laurence Steinberg is a noted expert on adolescence (e.g., Steinberg, 2014). He is also a father.

When my son, Benjamin, was 14, he and three of his friends decided to sneak out of the house where they were spending the night and visit one of their girlfriends at around two in the morning. When they arrived at the girl’s house, they positioned themselves under her bedroom window, threw pebbles against her windowpanes, and tried to scale the side of the house. Modern technology, unfortunately, has made it harder to play Romeo these days. The boys set off the house’s burglar alarm, which activated a siren and simultaneously sent a direct notification to the local police station, which dispatched a patrol car. When the siren went off, the boys ran down the street and right smack into the police car, which was heading to the girl’s home. Instead of stopping and explaining their activity, Ben and his friends scattered and ran off in different directions through the neighborhood. One of the boys was caught by the police and taken back to his home, where his parents were awakened and the boy questioned.

I found out about this affair the following morning, when the girl’s mother called our home to tell us what Ben had done…. After his near brush with the local police, Ben had returned to the house out of which he had snuck, where he slept soundly until I awakened him with an angry telephone call, telling him to gather his clothes and wait for me in front of his friend’s house. On our drive home, after delivering a long lecture about what he had done and about the dangers of running from armed police in the dark when they believe they may have interrupted a burglary, I paused.

“What were you thinking?” I asked.

“That’s the problem, Dad,” Ben replied, “I wasn’t.”

[Steinberg, 2004, pp. 51, 52]

Steinberg realized that his son was right: When emotions are intense, especially when friends are nearby, the logical part of the brain shuts down. This shutdown is not reflected in questionnaires that require teenagers to respond to paper-and-pencil questions regarding hypothetical dilemmas. On those tests, most teenagers think carefully and answer correctly. In fact, when strong emotions are not activated, teenagers may be more logical than adults (Casey & Caudle, 2013). They remember facts they have learned in biology or health class about sex and drugs. However,

the prospect of visiting a hypothetical girl from class cannot possibly carry the excitement about the possibility of surprising someone you have a crush on with a visit in the middle of the night. It is easier to put on a hypothetical condom during an act of hypothetical sex than it is to put on a real one when one is in the throes of passion. It is easier to just say no to a hypothetical beer than it is to a cold frosty one on a summer night.

[Steinberg, 2004, p. 53]

Ben reached adulthood safely. Some other teenagers, with less cautious police or less diligent parents, do not. Brain immaturity makes teenagers vulnerable to social pressures and stresses, which typically bombard young people today (Casey & Caudle, 2013).

Indeed, brain immaturity coupled with the stresses of adolescence may help explain why many types of psychopathology increase at puberty, especially when puberty is early. Two experts write that “higher rates of psychopathology among early maturers are expected because their slow-developing neurocognitive systems are mismatched with the fast-approaching social and affective challenges at the onset of puberty” (Ge & Natsuaki, 2009, p. 329).

Of course, as with all the changes of adolescence, social context is crucial. It is as irrational for adults to blame teenage problems solely on their brains as it is for teenagers to follow every impulse.

Source: Annals of the New York Academy of Sciences by New York Academy of Sciences; HighWire Press Reproduced with permission of NEW YORK ACADEMY OF SCIENCES in the format Educational/Instructional Program via Copyright Clearance Center

The normal sequence of brain maturation (limbic system at puberty, then prefrontal cortex sometime in the early 20s) combined with the earlier onset of puberty means that, for contemporary teenagers, emotions rule behavior for a decade. The limbic system makes powerful sensations—loud music, speeding cars, strong drugs—compelling.

It is not that the prefrontal cortex shuts down. Actually, it continues to mature throughout childhood and adolescence, and, when they think about it, adolescents are able to assess risks better than children are (Pfeifer et al., 2011). The balance and coordination between the various parts of the brain is awry, even as the brain continues to develop (Casey et al., 2011).

When stress, arousal, passion, sensory bombardment, drug intoxication, or deprivation is extreme, the adolescent brain is flooded with impulses that might shame adults. Teenagers brag about being so drunk that they were “wasted,” “bombed,” “smashed”—a state most adults try to avoid and would not admit.

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Also, unlike most adults, many teenagers choose to spend a night without sleep, to eat nothing all day, to exercise in pain, or to risk parenthood or an STI by not using a condom. The parts of the brain dedicated to analysis are immature until long after the first hormonal rushes and sexual urges begin.

Sadly, teenagers have access to fast cars, lethal weapons, and dangerous drugs before their brains are ready. My friend said to his neighbor, who gave his son a red convertible for high school graduation, “Why didn’t you just give him a loaded gun?” The mother of the 20-year-old who killed 20 children and 7 adults (including the mother) in Newtown, Connecticut, did just that.

A more common example of the cautious part of the brain being overwhelmed by emotions comes from teens sending text messages while they are driving. In one survey, among U.S. high school seniors who have driven a car in the past month, 60 percent texted while driving, even though that is illegal almost everywhere (MMWR, June 13, 2014).

More generally, despite quicker reflexes and better vision than adults, far more teenagers die in motor-vehicle accidents than older drivers do. Thoughtless impulses and poor decisions are almost always to blame, not skill.

Any decision, from whether to eat a peach to where to go to college, requires balancing risk and reward, caution and attraction. Experiences, memories, emotions, and the prefrontal cortex help people choose to avoid some actions and perform others. Since the reward parts of adolescents’ brains are stronger than the inhibition parts (Luna et al., 2013), many adolescents act in ways that seem foolhardy to adults.

Benefits of Adolescent Brain Development

It is easy to criticize adolescent behavior and blame it on hormones, peers, culture, or the latest chosen culprit, brains. Yet remember that difference is not always deficit. Gains as well as losses are part of every developmental period. There are benefits as well as hazards in the adolescent brain.

Yes, Not No Diving into cold water with your friends is thrilling if you are a teenage boy and a girl is watching. Adult prohibition increases the joy.

For instance, with increased myelination and slower inhibition, reactions become lightning fast. Such speed is valuable, making adolescent athletes potential superstars, quick and fearless as they steal a base, tackle a fullback, or sprint when their lungs feel about to burst. Ideally, coaches have the wisdom to channel such bravery.

Furthermore, as the brain’s reward areas activate positive neurotransmitters, teenagers become happier. A new love, a first job, a college acceptance, or even an A on a term paper can produce a rush of joy, to be remembered and cherished lifelong.

Societies need some people who question assumptions, and adolescents are primed to question everything, often raising issues that need to be raised. As social and ecological circumstances change, someone needs to think critically about having lots of children, or eating bacon every breakfast, or burning fossil fuels. If tradition were never questioned, customs would ossify, and societies die.

Further, teenagers need to take risks and learn new things, because “the fundamental task of adolescence—to achieve adult levels of social competence—requires a great deal of learning about the social complexities of human social interactions” (Peper & Dahl, 2013, p. 135). That is exactly what their brains enable adolescents to do.

Synaptic growth enhances moral development as well. Adolescents question their elders and forge their own standards. Values embraced during adolescence are more likely to endure than those acquired later, after brain connections are firmly established. This is an asset if adolescent values are less self-centered than those of children or are more culturally attuned than those of older generations.

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Thus the developing prefrontal cortex “confers benefits as well as risks. It helps explain the creativity of adolescence and early adulthood, before the brain becomes set in its ways” (Monastersky, 2007, p. A17). The emotional intensity of adolescents “intertwines with the highest levels of human endeavor: passion for ideas and ideals, passion for beauty, passion to create music and art” (Dahl, 2004, p. 21). One application: Since adolescents are learning lessons about life, adults who care about the next generation need to ensure those lessons are good ones.

SUMMING UP   The brain develops unevenly during adolescence, with the limbic system ahead of the prefrontal cortex. That makes the brain’s reward centers more active than the cautionary areas, especially when adolescents are with each other. As a result, adolescents are quick to react, before having second thoughts or considering consequences. Without impulse control, anger can lead to hurtful words or even serious injury, lust can lead to disease or pregnancy, self-hatred can lead to self-destruction. These same brain qualities can be positive, as adolescents fall in love, throw themselves into work or study, question social traditions that are no longer relevant. Adolescent brain development allows joy and despair; teenagers are vulnerable to some of the best as well as some of the worst experiences life has to offer.

WHAT HAVE YOU LEARNED?

  1. Question 14.19

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    Brain scans that repeatedly compare the proportion of gray matter from childhood through adolescence reveal important changes. Gray matter (which refers to the cell bodies of neurons, which are less prominent with age as some neurons are unused), is reduced as white matter increases, in part because of pruning during the teen years. This allows intellectual connections to build. However, brain scans confirm that emotional control, revealed by fMRI studies, is not fully developed until adulthood. During adolescence, the prefrontal cortex is limited in connections and engagement.
  2. Question 14.20

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    When compared with the brains of emerging adults, adolescent brains show heightened arousal in the brain's reward centers. Teens seek excitement and pleasure, especially the social pleasure of a peer's admiration. In fact, when others are watching, teens find it thrilling to take dramatic risks that produce social acclaim, risks they would not dare take alone. The fact that the frontal lobes are the last to mature may explain something that has long bewildered adults: Especially when they are with their friends, many adolescents seek the thrill of new experiences and sensations, forgetting the caution that their parents have tried to instill.
  3. Question 14.21

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    Because the frontal lobe is still maturing, emotions rule adolescent behavior. They take risks, such as driving fast and texting while they are driving. Thoughtless impulses and poor decisions are almost always to blame when teenagers die in motor–vehicle accidents.
  4. Question 14.22

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    The limbic system matures before the prefrontal cortex, thus creating a situation in which impulsivity reigns relatively unchecked by logical thought. Therefore, adolescents take risks that adults would never consider.
  5. Question 14.23

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    Compared to adults, adolescents have: 1) Faster reaction time; 2) Increased positive emotions; 3) Easier acquisition of new ideas; 4) Enhanced moral development; and 5) Willingness to question tradition and try new things.