骁龙616联发科x10:青少年的大脑

Teenage Brains

青少年的大脑

Beautiful Brains

Moody. Impulsive. Maddening. Why do teenagers act the way they do? Viewed through the eyes of evolution, their most exasperating traits may be the key to success as adults.

喜怒无常、冲动任性、惹人讨厌。青少年为什么会如此行事呢？从进化的角度来看，他们让人恼火的特点中大多数可能是成年时取得成功的关键。

By David Dobbs

撰文：大卫·多布斯（David Dobbs）

Photograph by Kitra Cahana

摄影：克伊楚娃·卡阿纳（Kitra Cahana）

Although you know your teenager takes some chances, it can be a shock to hear about them.

虽然你明知道十几岁的孩子会冒险，但是听说了他们做的有些事你还是会感觉很震惊。

One fine May morning not long ago my oldest son, 17 at the time, phoned to tell me that he had just spent a couple hours at the state police barracks. Apparently he had been driving "a little fast." What, I asked, was "a little fast"? Turns out this product of my genes and loving care, the boy-man I had swaddled, coddled, cooed at, and then pushed and pulled to the brink of manhood, had been flying down the highway at 113 miles an hour.

不久之前，在五月份的一个美好的早晨，我的大儿子（那时他17岁）打电话告诉我说，他刚在州警察所度过了几个小时。很显然，他车开得“有点儿快了。”我问，什么叫“有点儿快”？结果，这个禀承了我的基因和关爱的产儿，这个我曾包在襁褓里、娇惯着、对他柔声细语的而如今已跌跌撞撞来到成年边缘的小男人，竟然以每小时113英里的速度在高速公路上飞驰。

"That's more than a little fast," I said.

“那可不是什么有点儿快，”我说。

He agreed. In fact, he sounded somber and contrite. He did not object when I told him he'd have to pay the fines and probably for a lawyer. He did not argue when I pointed out that if anything happens at that speed—a dog in the road, a blown tire, a sneeze—he dies. He was in fact almost irritatingly reasonable. He even proffered that the cop did the right thing in stopping him, for, as he put it, "We can't all go around doing 113."

他表示同意。事实上，他的声音听起来又沮丧又后悔。我说他得自己付罚金，如果必要的话还要自己付律师费，他都没有表示反对。我说如果以那种速度开车时发生了什么事——路上出现一条狗，爆胎，打了个喷嚏——他可能就没命了，他也没有争辩。实际上，他通情达理得都让人恼火。他甚至说那个制止他的警察做得很对，因为，正如他指出的，“大家不能总是每小时开113英里。”

He did, however, object to one thing. He didn't like it that one of the several citations he received was for reckless driving.

但是，他对一件事表示反对。他讨厌“鲁莽驾驶”（对他指控的罪名之一）的说法。

"Well," I huffed, sensing an opportunity to finally yell at him, "what would you call it?"

“哦，”我被激怒了，觉得终于逮着机会冲他大吼了，“那你管这叫什么？”

"It's just not accurate," he said calmly. "?'Reckless' sounds like you're not paying attention. But I was. I made a deliberate point of doing this on an empty stretch of dry interstate, in broad daylight, with good sight lines and no traffic. I mean, I wasn't just gunning the thing. I was driving.

“那不够准确，”他冷静地说。“‘鲁莽’听起来就像你根本没过脑子。但我不是这样。我慎重考虑过这件事，选择了州际间一条空荡荡的高速公路，头上是大大的太阳，路上视线良好，根本没车经过。我的意思是说，我并没有开枪射击。我只是开车而已。”

"I guess that's what I want you to know. If it makes you feel any better, I was really focused."

“这就是我想对你说的。如果能让你感觉好点儿，我就算说到点儿上了。”

Actually, it did make me feel better. That bothered me, for I didn't understand why. Now I do.

事实上，那番话的确让我感觉好多了。但它也让我很困扰，我不明白为什么会那样。现在我懂了。

My son's high-speed adventure raised the question long asked by people who have pondered the class of humans we call teenagers: What on Earth was he doing? Parents often phrase this question more colorfully. Scientists put it more coolly. They ask, What can explain this behavior? But even that is just another way of wondering, What is wrong with these kids? Why do they act this way? The question passes judgment even as it inquires.

我儿子的高速冒险经历引出了一个问题，这也是探究青少年人群的人们长久以来一直在追问的一个问题：他到底在做什么？父母们的措词通常更加丰富多彩。而科学家会相对冷静些。他们问，如何解释这种行为？但就算只是换了一种提问方式，这些孩子到底怎么了？为什么他们会这样？提问时，问题本身就是种评判。

Through the ages, most answers have cited dark forces that uniquely affect the teen. Aristotle concluded more than 2,300 years ago that "the young are heated by Nature as drunken men by wine." A shepherd in William Shakespeare's The Winter's Tale wishes "there were no age between ten and three-and-twenty, or that youth would sleep out the rest; for there is nothing in the between but getting wenches with child, wronging the ancientry, stealing, fighting." His lament colors most modern scientific inquiries as well. G. Stanley Hall, who formalized adolescent studies with his 1904 Adolescence: Its Psychology and Its Relations to Physiology, Anthropology, Sociology, Sex, Crime, Religion and Education, believed this period of "storm and stress" replicated earlier, less civilized stages of human development. Freud saw adolescence as an expression of torturous psychosexual conflict; Erik Erikson, as the most tumultuous of life's several identity crises. Adolescence: always a problem.

古往今来，大多数答案中提及了影响青少年的独一无二的神秘力量。2300多年前，亚里士多德（Aristotle）指出“年轻人受天性驱使，就如醉汉受酒精驱使。”威廉·莎士比亚（William Shakespeare）《冬天的故事》（The Winter's Tale）中，牧羊人希望“孩子与成人之间不再有差别，年轻人以后能够安眠，因为二者之间本无差别，只有成人才会与孩子通奸、对古人不敬、偷窃、打仗。”他的挽歌也影响了现代大多数的科学探索。1904年，斯坦利·霍尔（G. Stanley Hall）在《青春期》一书中正式提出了他对青春期的研究成果：青春期的心理状态以及与生理学、人类学、社会学、性、犯罪、宗教和教育的关系，他认为，这个“狂风暴雨”时期是人类发展早期阶段、文明程度不高状态的重现。弗洛伊德（Freud）认为青少年体现了一种痛苦的精神性欲的冲突，而艾里克·埃里克森（Erik Erikson）认为青少年处于人生各阶段身份认同危机中最混乱的一个时期。青少年：反正就是麻烦。

Such thinking carried into the late 20th century, when researchers developed brain-imaging technology that enabled them to see the teen brain in enough detail to track both its physical development and its patterns of activity. These imaging tools offered a new way to ask the same question—What's wrong with these kids?—and revealed an answer that surprised almost everyone. Our brains, it turned out, take much longer to develop than we had thought. This revelation suggested both a simplistic, unflattering explanation for teens' maddening behavior—and a more complex, affirmative explanation as well.

这种想法一直持续到20世纪晚期，研究者开发了脑成像技术，通过这种技术可以看到青少年大脑中的许多细节，从而得以追踪大脑的生理发展和活动方式的情况。成像工具提供了一种新的提问方式——这些孩子怎么了？——也给出了一个几乎让所有人都感到意外的答案。结果表明，我们大脑的发展需要花费比我们以为的长得多的时间。这个新发现指出，对于青少年惹人讨厌的行为，无论是直白的、过分简单化的解释还是肯定的、过分复杂化的诠释，两者没什么分别。

The first full series of scans of the developing adolescent brain—a National Institutes of Health (NIH) project that studied over a hundred young people as they grew up during the 1990s—showed that our brains undergo a massive reorganization between our 12th and 25th years. The brain doesn't actually grow very much during this period. It has already reached 90 percent of its full size by the time a person is six, and a thickening skull accounts for most head growth afterward. But as we move through adolescence, the brain undergoes extensive remodeling, resembling a network and wiring upgrade.

20世纪90年代，第一次对青少年发展中的大脑进行全方位扫描（这是国家卫生研究院（NIH）的一个项目）旨在研究100多名青少年的成长过程，结果显示，我们的大脑在12岁到25岁之间经历了一次大规模的重组。这段时期，大脑并没有怎么长大。人6岁时，脑容量就已经达到成人的90%，之后头部发育主要就是头骨增厚。但是，随着我们度过青春期，大脑进行大面积重组，就像一次网络和线路升级。

For starters, the brain's axons—the long nerve fibers that neurons use to send signals to other neurons—become gradually more insulated with a fatty substance called myelin (the brain's white matter), eventually boosting the axons' transmission speed up to a hundred times. Meanwhile, dendrites, the branchlike extensions that neurons use to receive signals from nearby axons, grow twiggier, and the most heavily used synapses—the little chemical junctures across which axons and dendrites pass notes—grow richer and stronger. At the same time, synapses that see little use begin to wither. This synaptic pruning, as it is called, causes the brain's cortex—the outer layer of gray matter where we do much of our conscious and complicated thinking—to become thinner but more efficient. Taken together, these changes make the entire brain a much faster and more sophisticated organ.

刚开始，大脑的轴突（一种长的神经结构，神经元通过它向另一个神经元传递信号）在周围那层叫作髓鞘（大脑中的白色物质）的脂肪物质的包裹下逐渐绝缘化，最终，轴突的传输速度能增大一百倍。与此同时，树突（树枝状细胞突起，神经元通过它接受邻近轴突发出的信号）更加细化，而且最常使用的突触（小的化学连接体，轴突和树突通过它传递信息）数量增多功能增强。而那些很少使用的突触就开始萎缩。这种所谓的突触剪除使得大脑皮层（外层灰色物质，我们的意识和复杂的思考都是在那儿进行的）变薄但效率提高。综上所述，这些变化使整个大脑变成一个更灵活更精密的器官。

This process of maturation, once thought to be largely finished by elementary school, continues throughout adolescence. Imaging work done since the 1990s shows that these physical changes move in a slow wave from the brain's rear to its front, from areas close to the brain stem that look after older and more behaviorally basic functions, such as vision, movement, and fundamental processing, to the evolutionarily newer and more complicated thinking areas up front. The corpus callosum, which connects the brain's left and right hemispheres and carries traffic essential to many advanced brain functions, steadily thickens. Stronger links also develop between the hippocampus, a sort of memory directory, and frontal areas that set goals and weigh different agendas; as a result, we get better at integrating memory and experience into our decisions. At the same time, the frontal areas develop greater speed and richer connections, allowing us to generate and weigh far more variables and agendas than before.

这个成熟期一直持续到青春期（以前人们以为在小学阶段就已经大部分都完成了）。20世纪90年代以来所做的脑成像显示，无论是从大脑后部到前部，还是从靠近脑干（执行古老的更基本的行为功能，比如，视力、运动和基本生命过程）的区域到进化得更新更复杂的思维区域，发生的生理变化是以慢波形式移动的。胼胝体（连接大脑左右两半球，负责传递对高级大脑功能有重要意义的信息）在稳步增厚。海马体（有点像计算机内存）和额叶（负责设定目标并权衡利弊）之间的联系也增强了，结果，我们做决定时就能更好地整合已有的记忆和经验。与此同时，额叶的速度加快联结也更丰富，我们就能比以前处理更多的变量和日常事项。

When this development proceeds normally, we get better at balancing impulse, desire, goals, self-interest, rules, ethics, and even altruism, generating behavior that is more complex and, sometimes at least, more sensible. But at times, and especially at first, the brain does this work clumsily. It's hard to get all those new cogs to mesh.

这个发展过程正常化以后，我们就能更好地协调冲动、欲望、目标、自私、规则、道德甚至是利他、反应生成行为（这更为复杂，至少是更理智）。但有时候，尤其是刚开始时，大脑并不擅长做这些。各部分很难协调运转。

Beatriz Luna, a University of Pittsburgh professor of psychiatry who uses neuroimaging to study the teen brain, used a simple test that illustrates this learning curve. Luna scanned the brains of children, teens, and twentysomethings while they performed an antisaccade task, a sort of eyes-only video game where you have to stop yourself from looking at a suddenly appearing light. You view a screen on which the red crosshairs at the center occasionally disappear just as a light flickers elsewhere on the screen. Your instructions are to not look at the light and instead to look in the opposite direction. A sensor detects any eye movement. It's a tough assignment, since flickering lights naturally draw our attention. To succeed, you must override both a normal impulse to attend to new information and curiosity about something forbidden. Brain geeks call this response inhibition.

皮兹堡大学（University of Pittsburgh）的精神病学教授贝亚特里斯·卢娜（Beatriz Luna）运用神经成像技术研究青少年的大脑，她通过一种简单测试说明了这种学习曲线。卢娜扫描了孩子、青少年和二十多岁人在执行非眼跳任务（有点儿像是一种只用眼睛玩的电子游戏，需要让自己不去看突然出现的亮光）时的大脑。每当屏幕上其他位置出现闪烁的光，你就要去看屏幕中央出现的红色十字光标。你收到的指令是不要去看亮光而要去看完全不同的方向。传感器会监测眼球运动。这项任务很难，因为人的注意力很容易被闪烁的光所吸引。为了完成任务，你必须不去理会想处理新信息的自然冲动以及对被禁止事物的好奇。大脑天才管这叫反应抑制。

Ten-year-olds stink at it, failing about 45 percent of the time. Teens do much better. In fact, by age 15 they can score as well as adults if they're motivated, resisting temptation about 70 to 80 percent of the time. What Luna found most interesting, however, was not those scores. It was the brain scans she took while people took the test. Compared with adults, teens tended to make less use of brain regions that monitor performance, spot errors, plan, and stay focused—areas the adults seemed to bring online automatically. This let the adults use a variety of brain resources and better resist temptation, while the teens used those areas less often and more readily gave in to the impulse to look at the flickering light—just as they're more likely to look away from the road to read a text message.

10岁孩子表现不理想，45%的时间都无法完成任务。青少年做得好一些。实际上，15岁的孩子如果有意识地抵制诱惑，他们就能做得和成人一样好，70%到80%的时间都能得分。但是，卢娜的发现中最有趣的并不是得分。而是她在人们做测试时的所做的脑部扫描。与成年人相比，青少年很少使用大脑的以下区域：监控行为、发现错误、做计划和保持专注，而成年人好像是“自动上线”。成年人运用大脑的各种资源有效地抵制诱惑，而较少使用那些区域的青少年通常更容易屈从于去看闪烁的光的冲动——正如他们更有可能不看路而去读短信。

If offered an extra reward, however, teens showed they could push those executive regions to work harder, improving their scores. And by age 20, their brains respond to this task much as the adults' do. Luna suspects the improvement comes as richer networks and faster connections make the executive region more effective.

但是，如果有额外奖励，青少年就能更努力运用那些执行区域，从而提高得分。20岁时，人的大脑对该任务的反应更加接近成年人。卢娜认为，更加丰富的神经网络和更加快速的连接速度使得执行区域更加有效。

These studies help explain why teens behave with such vexing inconsistency: beguiling at breakfast, disgusting at dinner; masterful on Monday, sleepwalking on Saturday. Along with lacking experience generally, they're still learning to use their brain's new networks. Stress, fatigue, or challenges can cause a misfire. Abigail Baird, a Vassar psychologist who studies teens, calls this neural gawkiness—an equivalent to the physical awkwardness teens sometimes display while mastering their growing bodies.

这些研究解释了为什么青少年会有令人恼火的前后矛盾的行为方式：早餐时令人愉悦，晚餐时令人讨厌；星期一是一副精明能干的派头，星期六变得就像魂游天外似的迷茫。他们普遍缺乏经验，还在学习如何使用大脑的新神经网络。压力、疲劳或挑战都会引发失败。瓦萨大学（Vassar）研究青少年的心理学家阿比盖尔·贝尔德（Abigail Baird）把这叫做神经笨拙（与青少年掌控成长中的身体时会表现出来的生理上的笨拙类同）。

The slow and uneven developmental arc revealed by these imaging studies offers an alluringly pithy explanation for why teens may do stupid things like drive at 113 miles an hour, aggrieve their ancientry, and get people (or get gotten) with child: They act that way because their brains aren't done! You can see it right there in the scans!

脑成像展现出的这些缓慢而不均匀的发展弧线提出一种简明却很有吸引力的解释，说明了青少年为什么会做些愚蠢的事，比如车速达到每小时113英里，冒犯传统，让人怀孕或怀孕：他们会这么做是因为他们的大脑根本没做事！这一点你在屏幕上看得很清楚！

This view, as titles from the explosion of scientific papers and popular articles about the "teen brain" put it, presents adolescents as "works in progress" whose "immature brains" lead some to question whether they are in a state "akin to mental retardation."

正如大量科学论文和科普文章的标题所示，这个观点把青少年描绘成“在成长中工作”，其“不成熟的大脑”导致一些人怀疑他们是否“类似于智力缺陷”。

The story you're reading right now, however, tells a different scientific tale about the teen brain. Over the past five years or so, even as the work-in-progress story spread into our culture, the discipline of adolescent brain studies learned to do some more-complex thinking of its own. A few researchers began to view recent brain and genetic findings in a brighter, more flattering light, one distinctly colored by evolutionary theory. The resulting account of the adolescent brain—call it the adaptive-adolescent story—casts the teen less as a rough draft than as an exquisitely sensitive, highly adaptable creature wired almost perfectly for the job of moving from the safety of home into the complicated world outside.

但是，你现在看的内容告诉你了另一种关于青少年大脑的不同的科学解释。在过去的五年左右，即使“在成长中工作”的说法传入我们的文化中，对青春期大脑进行研究的这门学科也学会了更加全面地考虑问题。一些研究者开始站在一种更积极、更讨好的角度看待近期大脑和基因的研究成果，这明显是受到了进化理论的影响。关于青少年大脑的最终描述（称其为适应性青少年的描述）不再将其看作一个草稿而是看作一个相当敏感、具有高度适应性的生物体，他们几乎等不及要离开家的安全港湾到外面复杂的世界去。

This view will likely sit better with teens. More important, it sits better with biology's most fundamental principle, that of natural selection. Selection is hell on dysfunctional traits. If adolescence is essentially a collection of them—angst, idiocy, and haste; impulsiveness, selfishness, and reckless bumbling—then how did those traits survive selection? They couldn't—not if they were the period's most fundamental or consequential features.

这种观点很可能有利于青少年。更重要的是，它符合了生物学自然选择的最基本规则。选择对有功能障碍的特性非常不利。如果青少年本质上是这种集合体——焦虑、愚蠢、轻率，冲动、自私和不计后果、笨手笨脚——那么这些特性是如何经过选择而存在的呢？如果它们不是这个时期最基本或最重要的特性，就不可能存在。

The answer is that those troublesome traits don't really characterize adolescence; they're just what we notice most because they annoy us or put our children in danger. As B. J. Casey, a neuroscientist at Weill Cornell Medical College who has spent nearly a decade applying brain and genetic studies to our understanding of adolescence, puts it, "We're so used to seeing adolescence as a problem. But the more we learn about what really makes this period unique, the more adolescence starts to seem like a highly functional, even adaptive period. It's exactly what you'd need to do the things you have to do then."

答案是，那些令人恼火的特性并未真正描绘出青少年的个性；它们只是我们关注最多的东西，因为它们激怒了我们或者说把孩子们置于危险境地。威尔康奈尔医学院（Weill Cornell Medical College）的神经科学家凯西（B. J. Casey）花了将近十年时间对大脑和基因进行研究，让我们得以了解青春期，他指出“我们太过习惯把青少年当作麻烦了。但是，我们对到底是什么令这段时期如此独特这一问题研究得越多，青春期就越像是一个高度功能化甚至颇具适应性的时期。他们需要去做他们不得不做的事。”

To see past the distracting, dopey teenager and glimpse the adaptive adolescent within, we should look not at specific, sometimes startling, behaviors, such as skateboarding down stairways or dating fast company, but at the broader traits that underlie those acts.

过去无论是把青少年看作精神涣散迷迷糊糊的，还是将其看作具有内在适应性的，我们都不应该只留意那些偶尔出现的令人吃惊的特定行为，比如踩着滑板从楼梯上滑下来或与约会对象分分合合，而应该注意那些隐藏在这些行为背后的更具普遍性的品质。

Let's start with the teen's love of the thrill. We all like new and exciting things, but we never value them more highly than we do during adolescence. Here we hit a high in what behavioral scientists call sensation seeking: the hunt for the neural buzz, the jolt of the unusual or unexpected.

让我们从青少年对刺激感的热爱开始。人都喜欢新鲜刺激的事物，但只有青春期时才如此看重这些。这里我们上升到了一个高度，行为科学家叫做感觉寻求：寻求精神刺激、罕见或意外带来的强烈感受。

Seeking sensation isn't necessarily impulsive. You might plan a sensation-seeking experience—a skydive or a fast drive—quite deliberately, as my son did. Impulsivity generally drops throughout life, starting at about age 10, but this love of the thrill peaks at around age 15. And although sensation seeking can lead to dangerous behaviors, it can also generate positive ones: The urge to meet more people, for instance, can create a wider circle of friends, which generally makes us healthier, happier, safer, and more successful.

寻求感觉不一定是冲动。你可能做了计划——延缓张伞跳伞或飞车——而且非常谨慎，就像我儿子做的一样。冲动从10岁左右开始，通常延续终生，但这种对刺激感的热爱在15岁就达到顶峰。虽然感觉寻求会引发危险行为，但它也有积极的一面：比如，想认识更多的人能够形成更大的朋友圈子，这种行为通常会让我们更健康、更幸福、更安全也更成功。

This upside probably explains why an openness to the new, though it can sometimes kill the cat, remains a highlight of adolescent development. A love of novelty leads directly to useful experience. More broadly, the hunt for sensation provides the inspiration needed to "get you out of the house" and into new terrain, as Jay Giedd, a pioneering researcher in teen brain development at NIH, puts it.

这可能解释了为什么对新事物保持开放态度（不过有时可能是杀猫事件）仍然是青少年发展中的一个亮点。猎奇带来了有用的经验。正如杰伊·吉德（Jay Giedd）（国家卫生研究所（NIH）研究青少年大脑的一位先驱研究者）所说，从更广泛的角度来看，寻求感觉为“走出家门”进入新环境提供了必要的激励。

Also peaking during adolescence (and perhaps aggrieving the ancientry the most) is risk-taking. We court risk more avidly as teens than at any other time. This shows reliably in the lab, where teens take more chances in controlled experiments involving everything from card games to simulated driving. And it shows in real life, where the period from roughly 15 to 25 brings peaks in all sorts of risky ventures and ugly outcomes. This age group dies of accidents of almost every sort (other than work accidents) at high rates. Most long-term drug or alcohol abuse starts during adolescence, and even people who later drink responsibly often drink too much as teens. Especially in cultures where teenage driving is common, this takes a gory toll: In the U.S., one in three teen deaths is from car crashes, many involving alcohol.

冒险在青春期也达到最高峰（也许还有最激烈地冒犯传统）。法庭审讯青少年的冒险行为比其他任何时候都多。这一点也在实验室得到验证，青少年在控制实验中更倾向于冒险，无论是纸牌游戏还是模拟驾驶都是如此。这表明，在现实生活中，大约15到25岁之间，各种冒险行为和危险结果都达到顶峰。这个年龄段死于意外的几乎在各方面（除了工作事故之外）都占很高比率。长期滥用毒品或酗酒大都开始于青春期，甚至那些后来节制饮酒的人在青春期通常会饮酒过度。特别是在允许青少年驾驶的文化背景中，冒险使其付出了惨痛的代价：在美国，三分之一的青少年死于车祸，其中有些是酒后驾驶。

Are these kids just being stupid? That's the conventional explanation: They're not thinking, or by the work-in-progress model, their puny developing brains fail them.

这些孩子很蠢吗？传统的解释是：他们不过脑子或只是个正在发展中的模型，微不足道的发展中的大脑让他们失败连连。

Yet these explanations don't hold up. As Laurence Steinberg, a developmental psychologist specializing in adolescence at Temple University, points out, even 14- to 17-year-olds—the biggest risk takers—use the same basic cognitive strategies that adults do, and they usually reason their way through problems just as well as adults. Contrary to popular belief, they also fully recognize they're mortal. And, like adults, says Steinberg, "teens actually overestimate risk."

但是，没有证据支持这些说法。坦普尔大学（Temple University）专门研究青少年的发展心理学家劳伦斯·斯坦伯格（Laurence Steinberg）指出，即使在14到17岁那个最具冒险精神的年龄段，青少年运用的基本认知策略与成年人也一样，他们通常通过问题思考道理，这就跟成年人是一样的。同人们的一般认识相反，他们根本不是不知死活。斯坦伯格说，跟成年人一样，“青少年只是低估了危险。”

So if teens think as well as adults do and recognize risk just as well, why do they take more chances? Here, as elsewhere, the problem lies less in what teens lack compared with adults than in what they have more of. Teens take more risks not because they don't understand the dangers but because they weigh risk versus reward differently: In situations where risk can get them something they want, they value the reward more heavily than adults do.

所以，如果青少年跟成年人的思维方式一样，也知道危险，那他们为什么还要去冒险？这就跟其他方面是一样的，问题不在于跟成年人相比他们缺少了什么，而在于他们多了些什么。青少年倾向于冒险，不是因为他们不知道危险而是因为他们对风险和回报的看法与成年人不同：当冒险能让他们得到自己想要的东西时，他们就会把回报看得更重要（与成年人相比）。

A video game Steinberg uses draws this out nicely. In the game, you try to drive across town in as little time as possible. Along the way you encounter several traffic lights. As in real life, the traffic lights sometimes turn from green to yellow as you approach them, forcing a quick go-or-stop decision. You save time—and score more points—if you drive through before the light turns red. But if you try to drive through the red and don't beat it, you lose even more time than you would have if you had stopped for it. Thus the game rewards you for taking a certain amount of risk but punishes you for taking too much.

斯坦伯格通过电子游戏很好地说明了这一点。游戏中，你要在最短时间内驱车穿越城市。沿途有几个交通信号灯。跟现实生活一样，你靠近交通信号灯时，它有时会从绿灯变黄灯，让你必须快速决定穿过或停下。如果你在变红灯前开了过去，你用的时间会更少，得分也就更高。但如果你尝试这么做却没成功，那么你就会比停下来等花费更多时间。因此，在这个游戏中，冒险会得到奖励，而过于冒险就会受到惩罚。

When teens drive the course alone, in what Steinberg calls the emotionally "cool" situation of an empty room, they take risks at about the same rates that adults do. Add stakes that the teen cares about, however, and the situation changes. In this case Steinberg added friends: When he brought a teen's friends into the room to watch, the teen would take twice as many risks, trying to gun it through lights he'd stopped for before. The adults, meanwhile, drove no differently with a friend watching.

       青少年独自驾驶时，如斯坦伯格形象化地称为“冷静”的情况下（独自在一间空房子里），他们冒险的机率与成年人相似。但是，如果增加了青少年在意的奖励，情况就不同了。斯坦伯格把朋友加进来的情况下：当他带着青少年的朋友到房间来观看时，青少年冒险的机率提高了两倍，在之前他会停下来的亮灯的地方现在会拼命冲过去。但，在有朋友观看的情况下，成年人开车没有什么变化。

To Steinberg, this shows clearly that risk-taking rises not from puny thinking but from a higher regard for reward.

对斯坦伯格而言，这清楚地表明，冒险增加并非由于考虑不周而是由于回报增加。

"They didn't take more chances because they suddenly downgraded the risk," says Steinberg. "They did so because they gave more weight to the payoff."

“他们倾向于冒更多险不是因为不重视危险，”斯坦伯格说。“这么做只是因为他们更看重回报。”

Researchers such as Steinberg and Casey believe this risk-friendly weighing of cost versus reward has been selected for because, over the course of human evolution, the willingness to take risks during this period of life has granted an adaptive edge. Succeeding often requires moving out of the home and into less secure situations. "The more you seek novelty and take risks," says Baird, "the better you do." This responsiveness to reward thus works like the desire for new sensation: It gets you out of the house and into new turf.

斯坦伯格和凯西这样的研究者相信，这种衡量成本和回报的适当冒险之所以存在，是因为在人类进化过程中，青春期冒险的意愿顺应了一种适应的优势。成功通常需要走出家门进入不够安全的环境。“你寻求越多的新奇和冒险，”贝尔德说，“你做得就越好。”这种对奖励的反应就像对新感觉的渴望一样在起作用：它让你走出家门进入新的活动领域。

As Steinberg's driving game suggests, teens respond strongly to social rewards. Physiology and evolutionary theory alike offer explanations for this tendency. Physiologically, adolescence brings a peak in the brain's sensitivity to dopamine, a neurotransmitter that appears to prime and fire reward circuits and aids in learning patterns and making decisions. This helps explain the teen's quickness of learning and extraordinary receptivity to reward—and his keen, sometimes melodramatic reaction to success as well as defeat.

正如斯坦伯格的开车游戏所指出的，青少年对社会奖励的反应很强烈。生理和演化理论都解释了这种趋势。生理上青少年对多巴胺（一种神经递质，重要的奖赏回路开关，对学习方式和做出决策起辅助作用）的敏感度达到顶峰。这有助于解释青少年学习速度快而且对奖励特别有感觉，而且他对成功的热衷就如同对失败的反应一样，有时候会很过激。

The teen brain is similarly attuned to oxytocin, another neural hormone, which (among other things) makes social connections in particular more rewarding. The neural networks and dynamics associated with general reward and social interactions overlap heavily. Engage one, and you often engage the other. Engage them during adolescence, and you light a fire.

青少年的大脑同样对催产素（另一种神经激素，（在各种其他事物中）使人从社会关系中感受到更多回报）很敏感。神经网络和动力系统（与一般奖励和社会互动相联系）有很多相互交叠的地方。触及一方面，通常就会涉及另一方面。青春期时触及了它们，就等于点燃了一团火。

This helps explain another trait that marks adolescence: Teens prefer the company of those their own age more than ever before or after. At one level, this passion for same-age peers merely expresses in the social realm the teen's general attraction to novelty: Teens offer teens far more novelty than familiar old family does.

这有助于解释另一种青少年身上的特质：青少年喜欢和同龄人在一起而不喜欢和比他们大或小的人在一起。在某个层面上，这种对同龄人的激情只是表达了青少年在社会领域中普遍为新奇事物所吸引：比起熟悉的家人，青少年彼此之间更具新奇性。

Yet teens gravitate toward peers for another, more powerful reason: to invest in the future rather than the past. We enter a world made by our parents. But we will live most of our lives, and prosper (or not) in a world run and remade by our peers. Knowing, understanding, and building relationships with them bears critically on success. Socially savvy rats or monkeys, for instance, generally get the best nesting areas or territories, the most food and water, more allies, and more sex with better and fitter mates. And no species is more intricately and deeply social than humans are.

但是，青少年为同龄人所吸引的另一个更为强大的原因是：投资对象是未来而非过去。我们进入一个由父母们组成的世界。但是我们将会活在由我们自己组成的世界里，而且将在这个由我们的同龄人掌控和重塑的世界里取得成功（或失败）。认识、理解并且和他们建立关系对成功有着决定性的影响。比如，在老鼠或猴子之类的群居动物中，富有社会经验的通常会得到最好的巢区或领域、最多的食物和水、更多的拥护者和与更优秀更健康的伴侣有更多的性活动。而且没有哪种生物的社会关系比人类更加复杂和精密。

This supremely human characteristic makes peer relations not a sideshow but the main show. Some brain-scan studies, in fact, suggest that our brains react to peer exclusion much as they respond to threats to physical health or food supply. At a neural level, in other words, we perceive social rejection as a threat to existence. Knowing this might make it easier to abide the hysteria of a 13-year-old deceived by a friend or the gloom of a 15-year-old not invited to a party. These people! we lament. They react to social ups and downs as if their fates depended upon them! They're right. They do.

这种具有决定性的人类特质使同伴关系不再是一件琐碎小事而成了一件头等大事。实际上，一些脑部扫描显示，我们的大脑对同伴排斥的反应与对威胁身体健康或食物供应的反应一样强烈。换句话说，在精神层面上，我们认为社会排斥是对生存的一种威胁。明白这一点就更容易接受一个13岁的孩子被朋友欺骗后表现出的歇斯底里或者是一个15岁的孩子没接到聚会邀请时表现出的闷闷不乐。这些人！我们为之惋惜。他们对社交中的起起落落表现得好象自己的命运取决于那些似的！他们是对的。的确如此。

Excitement, novelty, risk, the company of peers. These traits may seem to add up to nothing more than doing foolish new stuff with friends. Look deeper, however, and you see that these traits that define adolescence make us more adaptive, both as individuals and as a species. That's doubtless why these traits, broadly defined, seem to show themselves in virtually all human cultures, modern or tribal. They may concentrate and express themselves more starkly in modern Western cultures, in which teens spend so much time with each other. But anthropologists have found that virtually all the world's cultures recognize adolescence as a distinct period in which adolescents prefer novelty, excitement, and peers. This near-universal recognition sinks the notion that it's a cultural construct.

兴奋、新奇、冒险、同伴相随。这些特性不过意味着和朋友一起做一些愚蠢的新鲜事。但是，深入去看，你就会发现，无论是对个人而言还是对整个物种而言，这些特性（我们用来描述青少年的）使我们更具适应性。那就是为什么这些特性（广义上）毫无疑问地在人类几乎各种文化中都有所体现，无论是现代社会还是原始部落。现代西方社会可能表现得更突出更明显，那些青少年与同伴一起度过大量的时间。但人类学家发现，实际上世界上的所有文化都把青春期看作一个截然不同的时期，青少年喜欢新奇、刺激以及同伴。这个近乎普遍的认识弱化了一个概念，那就是青春期是一种文化构建的产物。

Culture clearly shapes adolescence. It influences its expression and possibly its length. It can magnify its manifestations. Yet culture does not create adolescence. The period's uniqueness rises from genes and developmental processes that have been selected for over thousands of generations because they play an amplified role during this key transitional period: producing a creature optimally primed to leave a safe home and move into unfamiliar territory.

文化无疑塑造了青春期。影响了青春期的表达方式和可能持续的时间。文化还放大了青春期的表现。但是，青春期并不是由文化创造出来的。这个时期的独一无二来自于基因和发展过程（这个过程经历了数千代的进化），因为在这个关键的转换时期青春期扮演了一种夸大的角色：催生一种最适宜准备离开安全的家进入不熟悉领域的生命体。

The move outward from home is the most difficult thing that humans do, as well as the most critical—not just for individuals but for a species that has shown an unmatched ability to master challenging new environments. In scientific terms, teenagers can be a pain in the ass. But they are quite possibly the most fully, crucially adaptive human beings around. Without them, humanity might not have so readily spread across the globe.

从家里搬出去是人类做过的最困难的事，也是最危险的事，这不只是对个人而言，也是对整个物种而言，它表现出一种要掌控新的挑战性环境的无与伦比的能力。从科学角度来看，青少年可能是个讨厌鬼，但他们很可能就是最出色最彻底的环境适应者。没有他们，人类可能就不会这么容易地遍及整个地球。

This adaptive-adolescence view, however accurate, can be tricky to come to terms with—the more so for parents dealing with teens in their most trying, contrary, or flat-out scary moments. It's reassuring to recast worrisome aspects as signs of an organism learning how to negotiate its surroundings. But natural selection swings a sharp edge, and the teen's sloppier moments can bring unbearable consequences. We may not run the risk of being killed in ritualistic battles or being eaten by leopards, but drugs, drinking, driving, and crime take a mighty toll. My son lives, and thrives, sans car, at college. Some of his high school friends, however, died during their driving experiments. Our children wield their adaptive plasticity amid small but horrific risks.

无论具有适应性的青少年的这种观点是多么正确，都很难得到认同——父母们处理青少年那些特别恼人、执拗或绝对令人恐慌的时刻越多就越如此。让人安心的是，人们可以把青少年令人担忧的方面看作生物体在学习如何与周围环境交涉的表现。但是，自然选择是把双刃剑，青少年的草率会带来令人无法承受的后果。我们可能不用去冒在宗教战斗中被杀的危险或是被美洲豹吃掉的危险，但是毒品、酗酒、飞车和犯罪造成了重大的损失。我儿子没车，他还好好地活着而且还在大学里茁壮成长。但是，他高中时的一些朋友已经在尝试飞车时死掉了。我们的孩子们在那些看似微小但却可怕的冒险中运用着他们的适应环境的可塑性。

We parents, of course, often stumble too, as we try to walk the blurry line between helping and hindering our kids as they adapt to adulthood. The United States spends about a billion dollars a year on programs to counsel adolescents on violence, gangs, suicide, sex, substance abuse, and other potential pitfalls. Few of them work.

当然，我们作父母的也很困惑，我们想尽力把握好一个度，以在孩子适应成年期这条路上提供帮助和进行阻止。美国每年大概花十亿美元制作节目建议青少年该如何处理暴力、帮派、自杀、性行为、药物滥用以及其他潜在危险。但很少起作用。

Yet we can and do help. We can ward off some of the world's worst hazards and nudge adolescents toward appropriate responses to the rest. Studies show that when parents engage and guide their teens with a light but steady hand, staying connected but allowing independence, their kids generally do much better in life. Adolescents want to learn primarily, but not entirely, from their friends. At some level and at some times (and it's the parent's job to spot when), the teen recognizes that the parent can offer certain kernels of wisdom—knowledge valued not because it comes from parental authority but because it comes from the parent's own struggles to learn how the world turns. The teen rightly perceives that she must understand not just her parents' world but also the one she is entering. Yet if allowed to, she can appreciate that her parents once faced the same problems and may remember a few things worth knowing.

但是我们能够帮上忙，而且的确帮上了忙。我们能够阻止世界上的一些最糟糕的风险并且推动青少年去适应剩下的风险。研究表明，父母以一种柔和但坚定的手段参与指导青少年，与之保持联系但允许其独立，他们的孩子通常会在现实生活中表现得更好。青少年想从朋友那里学习大部分但并非全部内容。某种程度上，某些情况下（父母要做的就是确定在什么情况下），青少年知道父母能提供某种智慧（这种知识之所以有价值不是因为父母的权威而是因为它是父母努力掌控变化的世界的经验）。青少年准确地察觉到她必须理解的不只是父母的世界更是她自己将要进入的世界。但是，如果条件允许的话，她会意识到她父母也曾经面临同样的问题，也会记住一些有必要知晓的事。

Meanwhile, in times of doubt, take inspiration in one last distinction of the teen brain—a final key to both its clumsiness and its remarkable adaptability. This is the prolonged plasticity of those late-developing frontal areas as they slowly mature. As noted earlier, these areas are the last to lay down the fatty myelin insulation—the brain's white matter—that speeds transmission. And at first glance this seems like bad news: If we need these areas for the complex task of entering the world, why aren't they running at full speed when the challenges are most daunting?

由此引出了一个让人疑惑的青少年大脑的最后一个不同之处，也是它的笨拙和非凡的适应性的最后一个关键点。这就是随着青少年缓慢的成熟期最后完成发育的前额区所具有的持久可塑性。如早先提到的，这些区域是最后停止髓鞘（大脑中的白色物质，能提高信息传输速度）化的。乍一看，这好像是个坏消息：如果我们在进入社会时需要这些区域来执行复杂任务，那么为什么面临最大挑战时它们却不能全速应战呢？

The answer is that speed comes at the price of flexibility. While a myelin coating greatly accelerates an axon's bandwidth, it also inhibits the growth of new branches from the axon. According to Douglas Fields, an NIH neuroscientist who has spent years studying myelin, "This makes the period when a brain area lays down myelin a sort of crucial period of learning—the wiring is getting upgraded, but once that's done, it's harder to change."

答案是，速度的获得以灵活性的失去为代价。髓鞘化的外层能够提高轴突的传输速度，但它也限制了轴突上新的分支生长。根据国家卫生研究院的神经科学家道格拉斯·菲尔兹（Douglas Fields）花了数年时间研究髓磷脂的结果来看，“这使得那个时期（大脑的一个区域停止产生髓磷脂的时候）成为学习的关键期——线路在升级，但升级一旦完成，就很难再发生改变。”

The window in which experience can best rewire those connections is highly specific to each brain area. Thus the brain's language centers acquire their insulation most heavily in the first 13 years, when a child is learning language. The completed insulation consolidates those gains—but makes further gains, such as second languages, far harder to come by.

各个脑区获得信息的渠道（通过这些渠道，经验能最大限度地对神经网路进行重组）是非常具体的。因此，大脑语言中枢的绝缘化主要在头13年中（也就是一个孩子学习语言的时期）完成。绝缘完成后已有收益得到巩固，但新的收益（比如学习第二外语）就会受到妨碍。

So it is with the forebrain's myelination during the late teens and early 20s. This delayed completion—a withholding of readiness—heightens flexibility just as we confront and enter the world that we will face as adults.

因此，前脑的绝缘化是在青少年晚期和二十岁初期完成的。这个完成过程的延迟（也延迟了准备就绪）增强了我们以成人身份进入世界时的灵活性。

This long, slow, back-to-front developmental wave, completed only in the mid-20s, appears to be a uniquely human adaptation. It may be one of our most consequential. It can seem a bit crazy that we humans don't wise up a bit earlier in life. But if we smartened up sooner, we'd end up dumber.

这种长期的缓慢的从后到前的发展过程，直到25岁左右才结束，这好像是人类特有的一种适应能力。它可能也是我们最重要的适应能力之一。我们人类在生命早期并不明智，这听起来有点疯狂。但如果越早变聪明，我们最终就可能处于越愚蠢的境地。