美国国家公共电台 NPR--Want to understand your adolescent? Get to know their brain

Want to understand your adolescent? Get to know their brain

Transcript¹

For the parents of a teenager, adolescence² can be a challenging time. But to a brain scientist, it's a marvel³.

"I want people to understand that adolescence is not a disease, that adolescence is an amazing time of development," says Beatriz Luna, professor of psychiatry⁴ and pediatrics at the University of Pittsburgh.

That development is on display most afternoons at the Shaw Skatepark in Washington, D.C. It's a public site, filled with teens hanging out, taking risks, and learning new skills at a rapid pace.

"When you're younger, your mind is more open, and you're more creative, and nothing matters," says Leo De Leon, 13. "So you'll really try anything."

Leo has been skateboarding since he was 10. But getting the nerve to try a skate park for the first time was "kind of scary," he says. "I fell a lot when I first started. And I got hurt a lot."

Leo also got better — fast. And when he'd mastered one trick, he'd push himself to learn a new one, despite the risks.

"I was trying to ollie up something, and then I clipped it and my board went up and it hit me in my mouth," he says, "so now I have this scar."

Leo's also broken his arm and his elbows are a mess. But the payoff is, he can do things now like jump the flight of five stairs on the other side of the park.

"I kickflipped that one," he says. "It's on my Instagram."

Seeking new experiences

Leo's swift progress from frightened novice⁵ to accomplished⁶ skater shows the strengths of an adolescent brain.

"It's an incredible brain," Luna says. "It's just perfect for what it needs to do. And what it needs to do is gain experiences."

A child's brain goes through two critical periods of very rapid change.

The first happens about age 2, when most toddlers are busy walking, talking, climbing and falling. The second critical period begins around puberty.

"Adolescence is a time when the brain says, 'All right, you've had a lot of time now, we have to start making some decisions,'" Luna says

Decisions like which connections to get rid of.

"You're born with an excess of synaptic connections," Luna says. "And based on experience, you keep what you use and you lose what you don't use."

It's a process known as synaptic pruning⁷. And its imminent⁸ arrival may be one reason an adolescent brain seeks out new experiences, even if it means risking a broken arm or a broken heart.

During this period the brain is also optimizing⁹ the wiring it decides to keep.

"The connections that remain become myelinated," Luna says. "That means they're insulated with fatty tissue, which not only speeds neuronal transmission, but protects from any further changes."

Sex differences in the brain and in behavior

Adolescent brain changes tend to start earlier in girls than in boys. And around this time, males and females also begin to react differently to certain experiences — like stress.

That was one finding of an analysis of research on teens asked to perform tasks like solving an impossible math problem, or giving a talk to a group of strangers.

"Males' blood pressure was higher than females," Luna says. But when participants were asked about the experience later, males said, "Oh, it was fine," while females described it as "extremely stressful."

Luna says that suggests there are some sex differences in certain brain circuits. But it's not clear whether those differences are the result of genetics, hormones¹⁰, or social and cultural influences, she says.

Regardless, sex differences are just a small part of the big changes sweeping¹¹ through the brain during adolescence. And those changes continue throughout the teens and beyond.

"A lot of times people will think, oh, too late, they're adolescents," Luna says. "But no, because even though it is a time of vulnerabilities, it is also a window opportunity."

Adolescence, chimp¹² style

Adolescence isn't just for humans. It's also present in chimpanzees.

"There's something really charming about the chimps¹³ when they're going through this adolescent period," says Alexandra Rosati, an associate professor of sociology and anthropology¹⁴ at the University of Michigan. "They look kind of gangly. They have these new big teeth in their mouth."

And, of course, they are experiencing puberty.

"They're going through this physical change in the body and those same hormones are resculpting the brain, basically, during this period," Rosati says.

Part of this resculpting involves the willingness to take risks.

Rosati was part of a team that did a gambling¹⁵ experiment with 40 chimps of various ages at a sanctuary¹⁶ in the Republic of Congo.

The chimps had a choice. They could go for a sure thing: peanuts. Or they could select a mystery option that might be a boring cucumber or a delicious banana.

"Adolescent chimpanzees were more willing to make that gamble," Rosati says. "They were more likely to choose that risky¹⁷ option and hopefully get the banana, whereas adults were more likely to play it safe."

That suggests young humans and chimps are both predisposed to risky behavior.

"The fact that we see these shifts in risk taking in the chimps suggests that this is tracking something biological," Rosati says. "It's not something to do with human culture or the way children are exposed to the media or something."

For both species, Rosati says, there's a purpose to this kind of risk-taking. "This period of adolescent risk-taking lets children grow into adults who are learning to live independently," she says.

Risky business and dopamine

So how does the brain of an adolescent chimp or a human encourage risk-taking? With dopamine, a naturally occurring chemical involved in memory, motivation and reward.

Adolescent brains produce more dopamine and are more sensitive to the chemical than adult brains, says Adriana Galván, a professor of psychology¹⁸ at the University of California, Los Angeles.

That means a bigger payoff from positive experiences like eating a piece of chocolate, or just hanging out with friends.

"It's a feedback loop," she says, "because then you start thinking, well, that was pretty good. I'm going to get that to happen again."

This amped up reward system also helps young brains learn faster by pushing boundaries and constantly asking, "What happens when I do this?" Galván says, "because that is how we learn best."

But big rewards and fast learning can make the adolescent brain vulnerable to some behaviors that are damaging, rather than useful.

"If the behavior is doing drugs, the brain is saying, 'Oh, OK, this is what I should be paying attention to and devoting my neurons and my pathways to,'" Galván says. "So you strengthen that. And eventually that is how addiction¹⁹ happens."

The brain's vulnerability during adolescence is probably one reason so many adult smokers²⁰ picked up the habit as teens, Galván says.

Over the course of adolescence, though the brain's priorities change, she says. Early on, it gives more attention to positive experiences than painful ones. But then, the balance begins to shift.

That seems to be happening with Leo the skateboarder.

"I used to do a lot of stair sets," he says. "I feel like I'm old now because I can't really do them anymore because they hurt."

All of which suggests that Leo's brain is developing exactly the way it's supposed to.

1 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

2 adolescence   

n.青春期，青少年

参考例句：

• Adolescence is the process of going from childhood to maturity.青春期是从少年到成年的过渡期。
• The film is about the trials and tribulations of adolescence.这部电影讲述了青春期的麻烦和苦恼。

3 marvel   

vi.(at)惊叹vt.感到惊异；n.令人惊异的事

参考例句：

• The robot is a marvel of modern engineering.机器人是现代工程技术的奇迹。
• The operation was a marvel of medical skill.这次手术是医术上的一个奇迹。

4 psychiatry   

n.精神病学，精神病疗法

参考例句：

• The study appeared in the Amercian science Journal of Psychiatry.这个研究发表在美国精神病学的杂志上。
• A physician is someone who specializes in psychiatry.精神病专家是专门从事精神病治疗的人。

5 novice   

adj.新手的，生手的

参考例句：

• As a novice writer,this is something I'm interested in.作为初涉写作的人，我对此很感兴趣。
• She realized that she was a novice.她知道自己初出茅庐。

6 accomplished   

adj.有才艺的；有造诣的；达到了的

参考例句：

• Thanks to your help,we accomplished the task ahead of schedule.亏得你们帮忙,我们才提前完成了任务。
• Removal of excess heat is accomplished by means of a radiator.通过散热器完成多余热量的排出。

7 pruning   

n.修枝，剪枝，修剪v.修剪（树木等）( prune的现在分词 )；精简某事物，除去某事物多余的部分

参考例句：

• In writing an essay one must do a lot of pruning. 写文章要下一番剪裁的工夫。 来自《现代汉英综合大词典》
• A sapling needs pruning, a child discipline. 小树要砍，小孩要管。 来自《现代汉英综合大词典》

8 imminent   

adj.即将发生的，临近的，逼近的

参考例句：

• The black clounds show that a storm is imminent.乌云预示暴风雨即将来临。
• The country is in imminent danger.国难当头。

9 optimizing   

v.使最优化，使尽可能有效( optimize的现在分词 )；最佳化；寻优

参考例句：

• This model may be classified as either an optimizing model or simulation model. 这个模型可分为最佳化模型或模拟模型。 来自辞典例句
• Need to design crossover operator rationally while optimizing ANN. 优化网络需要合理设计交叉算子。 来自互联网

10 hormones   

n. 荷尔蒙，激素 名词hormone的复数形式

参考例句：

• This hormone interacts closely with other hormones in the body. 这种荷尔蒙与体內其他荷尔蒙紧密地相互作用。
• The adrenals produce a large per cent of a man's sex hormones. 肾上腺分泌人体的大部分性激素。

11 sweeping   

adj.范围广大的，一扫无遗的

参考例句：

• The citizens voted for sweeping reforms.公民投票支持全面的改革。
• Can you hear the wind sweeping through the branches?你能听到风掠过树枝的声音吗？

12 chimp   

n.黑猩猩

参考例句：

• In fact,the color of gorilla and chimp are light-color.其实大猩猩和黑猩猩的肤色是较为浅的。
• The chimp is the champ.猩猩是冠军。

13 chimps   

（非洲）黑猩猩( chimp的名词复数 )

参考例句：

• Chimps are too scarce, and too nearly human, to be routinely slaughtered for spare parts. 黑猩猩又太少，也太接近于人类，不可以作为人器官备用件说杀就杀。 来自英汉非文学 - 生命科学 - 医学的第四次革命
• And as nonprimates, they provoke fewer ethical and safety-related concerns than chimps or baboons. 而且作为非灵长类，就不会产生像用黑猩猩或狒狒那样的伦理和安全方面的顾虑。 来自英汉非文学 - 生命科学 - 医学的第四次革命

14 anthropology   

n.人类学

参考例句：

• I believe he has started reading up anthropology.我相信他已开始深入研究人类学。
• Social anthropology is centrally concerned with the diversity of culture.社会人类学主要关于文化多样性。

15 gambling   

n.赌博；投机

参考例句：

• They have won a lot of money through gambling.他们赌博赢了很多钱。
• The men have been gambling away all night.那些人赌了整整一夜。

16 sanctuary   

n.圣所，圣堂，寺庙；禁猎区，保护区

参考例句：

• There was a sanctuary of political refugees behind the hospital.医院后面有一个政治难民的避难所。
• Most countries refuse to give sanctuary to people who hijack aeroplanes.大多数国家拒绝对劫机者提供庇护。

17 risky   

adj.有风险的，冒险的

参考例句：

• It may be risky but we will chance it anyhow.这可能有危险，但我们无论如何要冒一冒险。
• He is well aware how risky this investment is.他心里对这项投资的风险十分清楚。

18 psychology   

n.心理，心理学，心理状态

参考例句：

• She has a background in child psychology.她受过儿童心理学的教育。
• He studied philosophy and psychology at Cambridge.他在剑桥大学学习哲学和心理学。

19 addiction   

n.上瘾入迷，嗜好

参考例句：

• He stole money from his parents to feed his addiction.他从父母那儿偷钱以满足自己的嗜好。
• Areas of drug dealing are hellholes of addiction,poverty and murder.贩卖毒品的地区往往是吸毒上瘾、贫困和发生谋杀的地方。

20 smokers   

吸烟者( smoker的名词复数 )

参考例句：

• Many smokers who are chemically addicted to nicotine cannot cut down easily. 许多有尼古丁瘾的抽烟人不容易把烟戒掉。
• Chain smokers don't care about the dangers of smoking. 烟鬼似乎不在乎吸烟带来的种种危害。