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If you turned 18 in the United States...
在美国，如果你满18岁……
Congrats, you're legally an adult.
那么恭喜你，在法律上你已经是成年人了。
Even if you're not doing your own laundry yet...
即使你还没有自己洗过衣服…
You're not your parents' responsibility anymore. I'm sure they're celebrating too...
你已不再是父母的责任了。我肯定他们也在庆祝…
But, here's the catch.
但问题是。
Even though you reached adulthood on paper;
即使名义上你已经成年，
Your brain still has more work to do
你的大脑并没有。
Ask a neuroscientist, and they'll tell you that people don't get to the so called adult brain until their thirties.
神经学家表示，人们直到三十多岁才步入所谓的成人大脑。
Or maybe even never.
或者可能永远不会。
That's because your brain never stops changing (even after you grow-up).
那是因为你的大脑从未停止变化（即使在你长大后）。
So, really, there's no such thing as a fully developed brain!
所以，真的，不存在完全发育的大脑！
Scientists are still learning a lot about brain development, but they've come a long way.
科学家们仍在学习有关大脑发育的许多知识，但他们已经取得了很大进展。
We used to think that you were born with all the neurons you would get.
我们曾经以为，人生来就具备所有的神经细胞。
But, now we know that new neurons and other brain cells can grow well into adulthood!
但是现在我们知道，新的神经细胞和其他脑细胞可以长到成年！
And the networks of connections between those neurons -- [which] let you learn, [and] think, and do things -- is also in flux.
这些神经细胞连接的网络——让你学习、思考和做事——也在不断变化。
So, your brain never really stops changing.
所以，大脑永远不会停止变化。
But, we do know it goes through developmental stages
但是，我们知道它会经历发展阶段，
After all, baby brains are really different from teen brains, which are really different from the brains of middle aged people.
毕竟，婴儿的大脑和青少年的大脑是不同的，青少年的大脑和中年人的大脑是不同的。
In terms of volume, your brain is full sized by the time you're ten, or so.
就体积而言，当你10岁左右的时候，你的大脑已经发育完全了。
You're born with most of your neurons, so in your first few years you're adding a lot of glial cells.
你生来就有大部分的神经细胞，在你出生的头几年，你会有很多神经胶质细胞。
Brain cells that help support neurons by feeding, insulating, and protecting them.
脑细胞为神经细胞提供供给、隔离和保护。
But it still has a lot of structural changes to under go; like a huge shift in the ratio of gray to white matter.
但还有许多结构性变化，比如灰质和白质比例的巨大转变。
Gray matter makes up the bulk of neurons while white matter is the stuff connecting it all together.
灰质构成了神经细胞的主体，而白质则是将其连接在一起的物质。
It's made of thin nerve fiber called axons surrounded by myelin -- a fatty substance that electrically insulates axons and speeds along brain signals.
它由一种被髓磷脂包围的称为轴突的薄神经纤维构成——一种将轴突绝缘并加速大脑信号传递的脂肪物质。
Now, both of these are important, but as kids start getting angsty (and move into their teenage years); they trade more gray matter for white matter.
现在，灰质和白质两个都很重要，但是随着孩子开始变得易怒（进入青春期），它们用更多的灰质来交换白质。
For one, the brain is laying down more myelin...
首先，大脑正在分泌更多的髓磷脂……
Which adds to white matter and lets neurons send information more quickly.
这增加了白质，让神经细胞更快地发送信息。
On top of that, the brain is also going through a kind of intense spring cleaning, and getting rid of connections that aren't being used.
最重要的是，大脑也在经历一场激烈的春季大扫除，清除那些无用的连接。
This process is called synaptic pruning.
这个过程叫做突触修剪。
It sounds a little weird because we tend to think more is better.
这听起来有点奇怪，因为我们往往认为脑细胞越多越好。
So how could fewer brain cells be a good thing?
那么，减少脑细胞怎么会是一件好事呢?
Well, synaptic pruning is thought to make the brain more efficient.
突触修剪被认为能使大脑更有效率。
There may be fewer neurons, and fewer contacts...
可能神经细胞更少，接触更少…
But that allows the brain to make better, stronger connections between different parts.
但这能让大脑不同部分之间的联系更好更强。
Scientists don't fully understand what these structural changes do, but they think that's one reason why you can eventually handle more complicated ideas.
科学家们还没有完全理解这些结构变化的作用，但他们认为这是你最终能够处理更复杂想法的原因之一。
Like, linear algebra (instead of just addition)
比如线性代数（而非增加物）
And these structural changes don't happen at the same rate for the entire brain.
这些结构变化在整个大脑中的速度并不相同。
We know that the visual center in the back of the brain seems to have things mostly wrapped up by the time you're 20 years old.
我们知道大脑后部的视觉中心似乎在20岁的时候就已经把所有的事情都处理好了。
But it takes [at least] another decade for the frontal lobe -- the part of the brain responsible for decision making and problem-solving (among other things) -- to do the same.
但额叶（大脑中负责决策和解决问题以及其他的部分）完成同样的工作至少还需要10年的时间。
There are also other ways for the brain to change as you grow up.
随着成长，大脑还有其他的变化方式。
Like, the number of neurotransmitter receptors on the brain cells, how good your brain is at using sugar, and [of course] hormones.
比如，脑细胞中神经递质受体的数量，大脑对糖的利用程度，当然还有激素。
[Can't forget hormones].
不能忘记荷尔蒙。
But, these aren't very well studied.
但是，这些并没有得到很好的研究。
We do know a couple things about teen brains and the behavioral transitions to adulthood, though...
不过，我们确实知道一些关于青少年的大脑和行为向成年人转变的事情……
Neuroscientists are finding that teen and young adult brains can function pretty well, but not necessarily all the time.
科学家发现，青少年和年轻人的大脑可以很好地运作，但不一定总是如此。
If you give teenagers cognitive tests (for instance), they can usually measure up to older adults, but not if they're scared
例如，如果给青少年进行认知测试，他们通常能达到老年人的水平，但如果他们害怕，就达不到。
In one 2016 experiment, researchers quizzed volunteers in three age ranges (13 to 17, 18 to 21, and 21 to 25)
2016年的一项实验中，研究人员对年龄在13至17岁、18至21岁和21至25岁之间的志愿者进行了测试。
and told them they might randomly blast a loud sound into the room.
然后告诉他们，他们可能会随机地向房间里发出一声巨响。
While slightly older adults were able to mostly ignore the threat of the noise...
稍微年长一点的成年人基本上可以忽略噪音的威胁。
Teenagers and young adults were thrown off.
青少年和年轻人就会很崩溃。
Scientist have found similar things when they give teens and young adults happy or sad emotional cues
科学家在给青少年或年轻人快乐或悲伤的情绪暗示时也发现了类似的事情
Which could mean [as cliché as it sounds]
这可能意味着（听起来很老套）
Teenager's brains aren't quite as good at regulating and processing emotions yet.
青少年的大脑还不太擅长调节和处理情绪。
Which could explain why some teens take more risks than older people.
这可以解释为什么有些青少年比老年人更爱冒险。
And, because those experiments involved [college aged] young adults too. It seems like this problem [if you want to call it that]...
而且，因为这些实验也涉及到（上大学的）年轻人。似乎（如果你想这么说的话）……
Doesn't magically go away once you turn 18.
一旦满18岁，就不会神奇地消失。
Neuroimaging studies suggest that this behaviour might be linked with be linked with less activity in the prefrontal cortex.
神经影像学研究表明，这种行为可能与前额皮质活动减少有关。
It's possible that the brain circuits that prevent emotions from overwhelming your ability to make decisions.
大脑中防止情绪压倒你做决定的能力的回路是可能的。
Don't fully develop until you're a little older.
长大一点才会完全发育。
Some researchers think that the definition of adulthood should really be when you've got more control over these kinds of emotional responses.
一些研究人员认为，成年的定义应该是当你对这些情绪有更多的控制反应。
Which for some people might be 22.
有些人可能是22岁。
But, for others, could be much later.
但对其他人来说，可能要晚得多。
As you get older and learn new skills you're strengthening connections and physically rearranging things.
随着年龄的增长和新技能的掌握，你会加强人际关系，重新安排生活。
So, even if you're over 18 and don't feel quite like a real adult yet.
所以，即使你已经超过18岁，还没觉得自己像个真正的成年人。
Take heart that your brain has more changing to do.
振作起来，你的大脑有更多的变化要做。
Thanks for watching this episode of SciShow Psych
感谢收看本期心理科学秀！
If you want to learn more about the practical side of adulting.
如果你想了解更多关于成人的实用内容。
Go check out how to adult at youtube.com/learnhowtoadult
去youtube.com/learnhowtoadult观看看我们的节目
Which has videos about everything from doing taxes to picking wine.
里面各种视频，应有尽有。
