大脑发育30岁才完成？
这两天，「大脑发育30岁才完成」的话题引发热议。真的是这样吗？
🤔️小作业：
A. The brain begins to eliminate some gray matter and increase white matter production.
B. The brain rapidly expands its gray matter due to newly forming synapses.
C. The brain's white matter begins to decrease while gray matter increases.
D. The brain's total volume begins to change dramatically.
A. Because people define adulthood based on different qualities.
B. Because the total volume of the brain doesn't change after adolescence.
C. Because brain development occurs in waves and at different times in different regions.
D. Because the concept of neurodevelopmental maturity is still not widely accepted.
无注释原文：
You're an adult, but your brain might not be, experts say
From: CNN
December 21, 2016
You're legally an adult when you turn 18, in most of the United States. However, from a scientific perspective, adulthood is an unsolved mystery.
Even neuroscientists don't know when adolescence ends and adulthood begins in the brain – after all, our brains are constantly changing, according to a new opinion paper published in the journal Neuron on Wednesday.
“There is no agreed-on benchmark that, when reached, would allow a neuroscientist to say ‘Aha! This brain is fully developed,' ” said Leah Somerville, an associate professor of psychology at Harvard University, who wrote the paper.
“However, it is safe to say that by almost any metric, the brain is continuing to develop actively well past the age of 18,” she said. “The reason I think it's important to discuss this issue is because policies impacting youth have begun to pay more and more attention to the concept of neurodevelopmental maturity, so neuroscientists have begun to get engaged in these complicated discussions,” such as debates about when to charge a child with an adult crime or when to permit aging out of the foster care system.
So, why can't the brain reveal whether you're an adult or not? Different parts of your brain mature at different times, Somerville said.
“Brain development occurs in waves, with different brain regions having their major developmental events at different times,” she said. “So, the measurements that index brain maturation will give you different answers depending on what measure you're focusing on and where in the brain you're looking.”
In other words, since there is no definitive way to measure brain maturity, there is no definitive age in which your brain signals that you are an adult.
Your brain consists of two types of tissue, gray matter and white matter. In your first decade of life, the gray matter grows and expands rapidly as many new synapses, or connections between nerves, are being made. The gray matter grows as you learn and are exposed to new experiences as a child.
Then, as your body prepares for puberty, your brain starts to prune back some of that gray matter and amp up its production of white matter, which allows different parts of the brain to share information better and faster, said Dr. Jess Shatkin, a child and adolescent psychiatrist at the Child Study Center at NYU Langone Medical Center, who was not involved in the new paper.
“The brain volume, the total volume, doesn't really change, but we lose about 1% of gray matter starting around 13 and we gain about 1% of white matter at the same time, and that trade off keeps going,” Shatkin said.
“There are big changes (in the brain) until the early 20s, and there may be pretty significant changes still until the early 30s,” he said. “We're still learning. Whereas, once upon a time, we imagined adolescence to end at 18, now we don't really know when this process of development ends. … Twenty-five, 26, 28, 30, 32? We don't know.”
Shatkin added that this maturation process of the brain tends to appear in female brains earlier than male brains.
“There's been some neurological data showing that girls' brains may begin to prune earlier,” he said. “This certainly goes along with what we typically observe clinically as well.”
Overall, most neuroscientists agree that “there's no magic age at which the brain reaches adulthood,” said Jeffrey Jensen Arnett, a research professor of psychology at Clark University in Massachusetts.
“I've been waiting to see a paper like this, and have thought of writing one myself,” he said. “I've done a lot of research on how people define adulthood, and people vary, but in general it's not an age, it's defined by qualities such as accepting responsibility for yourself and making independent decisions.”
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注：中文文本为机器翻译并非一一对应，仅供参考
含注释全文：
You're an adult, but your brain might not be, experts say
From: CNN
December 21, 2016
You're legally an adult when you turn 18, in most of the United States. However, from a scientific perspective, adulthood is an unsolved mystery.
在美国大部分地区，年满18岁就法定成年。然而，从科学的角度来看，成年期的界定仍是个未解之谜。
perspective
表示“（思考问题的）角度，观点，想法”，英文解释为“a particular way of considering something”举个🌰：Her attitude lends a fresh perspective to the subject. 她的态度为这一问题提供了新的视角。
Even neuroscientists don't know when adolescence ends and adulthood begins in the brain – after all, our brains are constantly changing, according to a new opinion paper published in the journal Neuron on Wednesday.
根据周三发表在《神经元》（Neuron）杂志上的一篇新观点论文，甚至神经科学家也不知道青春期何时结束，何时进入成年期——毕竟，我们的大脑在不断变化。
neuroscientist
表示“神经科学家”，英文解释为“a scientist who studies the nervous system and the brain”。
adolescence
adolescence /ˌædəˈlɛsəns/ 表示“青春期”，英文解释为“Adolescence is the period of your life in which you develop from being a child into being an adult.”
“There is no agreed-on benchmark that, when reached, would allow a neuroscientist to say ‘Aha! This brain is fully developed,' ” said Leah Somerville, an associate professor of psychology at Harvard University, who wrote the paper.
“没有公认的基准可以让神经科学家能够说‘哈！这个大脑已经完全发育了，’”论文作者哈佛大学心理学副教授利亚·萨默维尔（Leah Somerville）说。
benchmark
表示“基准”，英文解释为“something which can be measured and used as a standard that other things can be compared with”。
associate profess
associate professor /əˌsəʊ.si.ət prəˈfes.ər/ 表示“副教授”，英文解释为“a teacher of high rank in a college or university who has a lower rank than a professor”
“However, it is safe to say that by almost any metric, the brain is continuing to develop actively well past the age of 18,” she said. “The reason I think it's important to discuss this issue is because policies impacting youth have begun to pay more and more attention to the concept of neurodevelopmental maturity, so neuroscientists have begun to get engaged in these complicated discussions,” such as debates about when to charge a child with an adult crime or when to permit aging out of the foster care system.
“然而，几乎可以肯定的是，无论使用何种度量标准，大脑在18岁以后仍在不断发育，”她说。“我认为讨论这个问题很重要的原因是，对青少年产生影响的政策越来越关注神经发育成熟的概念，因此神经科学家已经开始参与这些复杂的讨论，”比如，何时以成年罪行起诉孩子，或者何时允许孩子从寄养系统中“成长出来”。
metric
metric /ˈmet.rɪk/ 作形容词，表示“公制的，米制的”，英文解释为“using or relating to a system of measurement that uses metres, centimetres, litres, etc.”举个🌰：The recipe is given in both metric and imperial measures. 制作方法以公制和英制两种计量方法标出。
作名词，它通常表示“度量标准”或“衡量指标”。它用于描述一种可以量化或衡量某个事物的标准或指标，英文解释为“a standard or measure for assessing something”。
maturity
maturity /məˈtʃʊə.rə.ti/ 1）表示“发育成熟，长成”，英文解释为“the state of being completely grown physically”举个🌰：How long does it take for the chicks to grow to maturity? 小鸡多长时间才能长大？
2）表示“（心智）成熟；成熟阶段；完善的状态”，英文解释为“the quality of behaving mentally and emotionally like an adult；a very advanced or developed form or state”
3）表示“（保险合同或投资）到期，开始有回报”，英文解释为“the time when an insurance agreement or investment becomes ready to be paid”举个🌰：The investment reaches maturity after ten years. 这项投资10年后开始获得回报。
foster
foster /ˈfɒs.tər/ 作动词，表示“鼓励；促进；培养”，英文解释为“to encourage the development or growth of ideas or feelings”举个🌰：I'm trying to foster an interest in classical music in my children. 我正努力培养我的孩子们对古典音乐的兴趣。
作形容词，表示“（在有限的一段时间内）（所）收养的，（所）代养的”，英文解释为“used to refer to someone or something connected with the care of children, usually for a limited time, by someone who is not the child's legal parent”如：a foster care/home/child/mother 非亲代养/寄养家庭/代养的孩子/养母。
So, why can't the brain reveal whether you're an adult or not? Different parts of your brain mature at different times, Somerville said.
那么，为什么大脑不能揭示你是否已成年呢？萨默维尔说，大脑的不同部位在不同时期成熟。
reveal
表示“揭露；泄露；透露”，英文解释为“to make known or show something that is surprising or that was previously secre”举个🌰：He was jailed for revealing secrets to the Russians. 他因为向俄国人泄密而被监禁。
“Brain development occurs in waves, with different brain regions having their major developmental events at different times,” she said. “So, the measurements that index brain maturation will give you different answers depending on what measure you're focusing on and where in the brain you're looking.”
“大脑的发展是波浪式的，不同的大脑区域在不同的时间有相应的关键发展阶段，”她说。“因此，对大脑发育是否成熟的度量会根据你关注的指标和大脑区域给出不同的答案。”
index
作动词，1）表示“为…编索引；把…编入索引”，英文解释为“to prepare an index for a book or collection, or arrange it in an index”举个🌰：Our computer indexes several thousand new records every second. 我们的计算机每秒钟可把几千个新记录编入索引。
2）表示“将…与…挂钩；使指数化”，英文解释为“to change a system of numbers according to each other or a fixed standard”举个🌰：Living expenses will be indexed to/in line with inflation (= to take inflation into consideration). 生活费用将与通货膨胀挂钩。
In other words, since there is no definitive way to measure brain maturity, there is no definitive age in which your brain signals that you are an adult.
换句话说，由于没有确切的方法来衡量大脑的成熟程度，所以没有一个确定的年龄可以表明你已经成年。
definitive
1）表示“最终的，决定性的；不可更改的”，英文解释为“not able to be changed or improved”如：a definitive judgment/ruling 最终的判决；
2）表示“最佳的；最完整可靠的”，英文解释为“considered to be the best of its type”举个🌰：He's written the definitive guide to Thailand. 他写出了最完整可靠的泰国旅游指南。
Your brain consists of two types of tissue, gray matter and white matter. In your first decade of life, the gray matter grows and expands rapidly as many new synapses, or connections between nerves, are being made. The gray matter grows as you learn and are exposed to new experiences as a child.
你的大脑由灰质和白质两种类型的组织组成。在你生命的前十年，随着许多新的突触或神经之间的连接被建立，灰质会迅速增长和扩张。你在儿童时期学习和接触新体验，灰质会随之增长。
tissue
表示“（动物或植物的细胞）组织”，英文解释为“a group of connected cells in an animal or plant that are similar to each other, have the same purpose, and form the stated part of the animal or plant”举个🌰：His face is covered with scar tissue where he was badly burned. 他脸上严重烧伤的地方满是疤痕。
synapse
synapse /ˈsaɪ.næps/ 表示“（神经元的）突触”，英文解释为“the point at which electrical signals move from one nerve cell to another”
Then, as your body prepares for puberty, your brain starts to prune back some of that gray matter and amp up its production of white matter, which allows different parts of the brain to share informpsychiatristation better and faster, said Dr. Jess Shatkin, a child and adolescent psychiatrist at the Child Study Center at NYU Langone Medical Center, who was not involved in the new paper.
然后，当你的身体准备进入青春期，你的大脑开始修剪一部分灰质，并增加白质的产生，这使得大脑的不同部位可以更好、更快地共享信息，纽约大学朗格内医学中心儿童研究中心的儿童和青少年精神病医生杰斯·沙特金博士（Dr. Jess Shatkin）表示。他并未参与这篇新论文的撰写。
puberty
puberty /ˈpjuːbətɪ/ 表示“青春期”，英文解释为“the stage in people's lives when they develop from a child into an adult because of changes in their body that make them able to have children”
prune
prune /pruːn/ 1）表示“修剪（树枝）”，英文解释为“to cut off branches from a tree, bush, or plant, especially so that it will grow better in the future”举个🌰：She spent the afternoon pruning roses. 她用下午的时间修剪了玫瑰。
2）表示“删除，删节”，英文解释为“to reduce something by removing things that are not necessary”举个🌰：I felt his essay needed a little pruning. 我认为他的文章需要稍作删节。
amp sth up
amp /æmp/ 表示“加大；加强”，英文解释为“to make something stronger, more extreme, or more exciting”举个🌰：They are amping up the pressure on their opponents. 他们正在给对手施加更大的压力。
psychiatrist
psychiatrist /saɪˈkaɪətrɪst/表示“精神病医生”，英文解释为“A psychiatrist is a doctor who treats people suffering from mental illness.”
“The brain volume, the total volume, doesn't really change, but we lose about 1% of gray matter starting around 13 and we gain about 1% of white matter at the same time, and that trade off keeps going,” Shatkin said.
“大脑总容量并不会发生太大变化，但在13岁左右开始我们会失去约1%的灰质，同时增加约1%的白质，这种增减交换会持续进行，”沙特金说。
volume
volume /ˈvɒl.juːm/ 1）表示“总数；总量；总额”，英文解释为“the number or amount of something in general”举个🌰：It's the sheer volume of traffic in the city that is causing the problems. 造成这些问题的就是城里的交通流量。
2）表示“容积；体积；容量”，英文解释为“the amount of space that is contained within an object or solid shape”举个🌰：Which of these bottles do you think has the greater volume? 你认为这些瓶子中哪个容积最大？
3）表示“卷；册”，英文解释为“one in a set of related books”也可以表示“书”，英文解释为“a book”如：如：a volume of poetry 一本诗集，举个🌰：She took a slim volume down from the shelf. 她从书架上取下一本很薄的书。
4）表示“音量；音量调节钮”，英文解释为“the level of sound produced by a television, radio, etc., or the switch or other device controlling this”举个🌰：Could you turn the volume down, please, I'm trying to sleep. 你能把音量调低些吗？我要睡觉。
trade-off
表示“（在需要而又相互对立的两者间的）权衡，协调；平衡，交换”，英文解释为“the act of balancing two things that you need or want but which are opposed to each other”举个🌰：There is a trade-off between the benefits of the drug and the risk of side effects. 在这种药的疗效和副作用之间有个权衡利弊的问题。
“There are big changes (in the brain) until the early 20s, and there may be pretty significant changes still until the early 30s,” he said. “We're still learning. Whereas, once upon a time, we imagined adolescence to end at 18, now we don't really know when this process of development ends. … Twenty-five, 26, 28, 30, 32? We don't know.”
“大脑在20岁出头之前会有很大的变化，甚至30岁出头之前可能还会有相当大的变化，”他说。“我们还在学习。曾几何时，我们认为青春期在18岁结束，现在我们真的不知道这个发育过程何时结束……25岁，26岁，28岁，30岁，32岁？我们不知道。”
Shatkin added that this maturation process of the brain tends to appear in female brains earlier than male brains.
沙特金补充说，女性大脑的这种成熟进程往往比男性的更早出现。
“There's been some neurological data showing that girls' brains may begin to prune earlier,” he said. “This certainly goes along with what we typically observe clinically as well.”
“有一些神经学数据显示，女孩的大脑可能会更早地开始修剪，”他说。“这确实与我们在临床上通常观察到的情况一致。”
clinically
clinically /ˈklɪn.ɪ.kəl.i/ 1）表示“临床诊断地”，英文解释为“according to medical science and examination of patients”举个🌰：Doctors pronounced him clinically dead. 医生宣布，根据临床诊断，他已经死亡。
2）表示“冷漠地；无动于衷地；无感情地”，英文解释为“in a way that lacks emotion or sympathy”举个🌰：Should doctors always remain clinically detached from their patients? 医生是否应该总是跟患者保持距离，不掺杂任何情感呢？
Overall, most neuroscientists agree that “there's no magic age at which the brain reaches adulthood,” said Jeffrey Jensen Arnett, a research professor of psychology at Clark University in Massachusetts.
总的来说，大多数神经科学家都认为，“大脑达到成年期没有魔法般的年龄界定，”马萨诸塞州克拉克大学心理学研究教授杰弗里·詹森·阿内特（Jeffrey Jensen Arnett）说。
“I've been waiting to see a paper like this, and have thought of writing one myself,” he said. “I've done a lot of research on how people define adulthood, and people vary, but in general it's not an age, it's defined by qualities such as accepting responsibility for yourself and making independent decisions.”
“我一直期待看到这样一篇论文，甚至考虑过自己写一篇，”他说。“我对人们如何定义成年做了很多研究，人们的定义各不相同，但总的来说，它不是一个年龄，而是由诸如接受为自己负责和做出独立决定等品质来定义的。”
- 今日要点 -
Legal vs. Neurological Adulthood
Adult at 18 legally, but brain continues developing
Brain Maturation
Different parts of brain mature at different times No definitive measure of maturity
Brain Composition Changes
Gray matter grows then prunes, white matter increases in puberty Changes continue into early 20s or 30s
Female vs. Male Brains
Female brains might mature earlier
Definition of Adulthood
No specific age for brain adulthood Adulthood defined by responsibility and independence
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