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If you turned 18 in the United States...
在美國，如果你滿18歲……
Congrats, you're legally an adult.
那么恭喜你，在法律上你已經是成年人了。
Even if you're not doing your own laundry yet...
即使你還沒有自己洗過衣服…
You're not your parents' responsibility anymore. I'm sure they're celebrating too...
你已不再是父母的責任了。我肯定他們也在慶祝…
But, here's the catch.
但問題是。
Even though you reached adulthood on paper;
即使名義上你已經成年，
Your brain still has more work to do
你的大腦并沒有。
Ask a neuroscientist, and they'll tell you that people don't get to the so called adult brain until their thirties.
神經學家表示，人們直到三十多歲才步入所謂的成人大腦。
Or maybe even never.
或者可能永遠不會。
That's because your brain never stops changing (even after you grow-up).
那是因為你的大腦從未停止變化（即使在你長大后）。
So, really, there's no such thing as a fully developed brain!
所以，真的，不存在完全發育的大腦！
Scientists are still learning a lot about brain development, but they've come a long way.
科學家們仍在學習有關大腦發育的許多知識，但他們已經取得了很大進展。
We used to think that you were born with all the neurons you would get.
我們曾經以為，人生來就具備所有的神經細胞。
But, now we know that new neurons and other brain cells can grow well into adulthood!
但是現在我們知道，新的神經細胞和其他腦細胞可以長到成年！
And the networks of connections between those neurons -- [which] let you learn, [and] think, and do things -- is also in flux.
這些神經細胞連接的網絡——讓你學習、思考和做事——也在不斷變化。
So, your brain never really stops changing.
所以，大腦永遠不會停止變化。
But, we do know it goes through developmental stages
但是，我們知道它會經歷發展階段，
After all, baby brains are really different from teen brains, which are really different from the brains of middle aged people.
畢竟，嬰兒的大腦和青少年的大腦是不同的，青少年的大腦和中年人的大腦是不同的。
In terms of volume, your brain is full sized by the time you're ten, or so.
就體積而言，當你10歲左右的時候，你的大腦已經發育完全了。
You're born with most of your neurons, so in your first few years you're adding a lot of glial cells.
你生來就有大部分的神經細胞，在你出生的頭幾年，你會有很多神經膠質細胞。
Brain cells that help support neurons by feeding, insulating, and protecting them.
腦細胞為神經細胞提供供給、隔離和保護。
But it still has a lot of structural changes to under go; like a huge shift in the ratio of gray to white matter.
但還有許多結構性變化，比如灰質和白質比例的巨大轉變。
Gray matter makes up the bulk of neurons while white matter is the stuff connecting it all together.
灰質構成了神經細胞的主體，而白質則是將其連接在一起的物質。
It's made of thin nerve fiber called axons surrounded by myelin -- a fatty substance that electrically insulates axons and speeds along brain signals.
它由一種被髓磷脂包圍的稱為軸突的薄神經纖維構成——一種將軸突絕緣并加速大腦信號傳遞的脂肪物質。
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.
現在，灰質和白質兩個都很重要，但是隨著孩子開始變得易怒（進入青春期），它們用更多的灰質來交換白質。
For one, the brain is laying down more myelin...
首先，大腦正在分泌更多的髓磷脂……
Which adds to white matter and lets neurons send information more quickly.
這增加了白質，讓神經細胞更快地發送信息。
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，大腦也在經歷一場激烈的春季大掃除，清除那些無用的連接。
This process is called synaptic pruning.
這個過程叫做突觸修剪。
It sounds a little weird because we tend to think more is better.
這聽起來有點奇怪，因為我們往往認為腦細胞越多越好。
So how could fewer brain cells be a good thing?
那么，減少腦細胞怎么會是一件好事呢?
Well, synaptic pruning is thought to make the brain more efficient.
突觸修剪被認為能使大腦更有效率。
There may be fewer neurons, and fewer contacts...
可能神經細胞更少，接觸更少…
But that allows the brain to make better, stronger connections between different parts.
但這能讓大腦不同部分之間的聯系更好更強。
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.
科學家們還沒有完全理解這些結構變化的作用，但他們認為這是你最終能夠處理更復雜想法的原因之一。
Like, linear algebra (instead of just addition)
比如線性代數（而非增加物）
And these structural changes don't happen at the same rate for the entire brain.
這些結構變化在整個大腦中的速度并不相同。
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.
我們知道大腦后部的視覺中心似乎在20歲的時候就已經把所有的事情都處理好了。
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.
但額葉（大腦中負責決策和解決問題以及其他的部分）完成同樣的工作至少還需要10年的時間。
There are also other ways for the brain to change as you grow up.
隨著成長，大腦還有其他的變化方式。
Like, the number of neurotransmitter receptors on the brain cells, how good your brain is at using sugar, and [of course] hormones.
比如，腦細胞中神經遞質受體的數量，大腦對糖的利用程度，當然還有激素。
[Can't forget hormones].
不能忘記荷爾蒙。
But, these aren't very well studied.
但是，這些并沒有得到很好的研究。
We do know a couple things about teen brains and the behavioral transitions to adulthood, though...
不過，我們確實知道一些關于青少年的大腦和行為向成年人轉變的事情……
Neuroscientists are finding that teen and young adult brains can function pretty well, but not necessarily all the time.
科學家發現，青少年和年輕人的大腦可以很好地運作，但不一定總是如此。
If you give teenagers cognitive tests (for instance), they can usually measure up to older adults, but not if they're scared
例如，如果給青少年進行認知測試，他們通常能達到老年人的水平，但如果他們害怕，就達不到。
In one 2016 experiment, researchers quizzed volunteers in three age ranges (13 to 17, 18 to 21, and 21 to 25)
2016年的一項實驗中，研究人員對年齡在13至17歲、18至21歲和21至25歲之間的志愿者進行了測試。
and told them they might randomly blast a loud sound into the room.
然后告訴他們，他們可能會隨機地向房間里發出一聲巨響。
While slightly older adults were able to mostly ignore the threat of the noise...
稍微年長一點的成年人基本上可以忽略噪音的威脅。
Teenagers and young adults were thrown off.
青少年和年輕人就會很崩潰。
Scientist have found similar things when they give teens and young adults happy or sad emotional cues
科學家在給青少年或年輕人快樂或悲傷的情緒暗示時也發現了類似的事情
Which could mean [as cliché as it sounds]
這可能意味著（聽起來很老套）
Teenager's brains aren't quite as good at regulating and processing emotions yet.
青少年的大腦還不太擅長調節和處理情緒。
Which could explain why some teens take more risks than older people.
這可以解釋為什么有些青少年比老年人更愛冒險。
And, because those experiments involved [college aged] young adults too. It seems like this problem [if you want to call it that]...
而且，因為這些實驗也涉及到（上大學的）年輕人。似乎（如果你想這么說的話）……
Doesn't magically go away once you turn 18.
一旦滿18歲，就不會神奇地消失。
Neuroimaging studies suggest that this behaviour might be linked with be linked with less activity in the prefrontal cortex.
神經影像學研究表明，這種行為可能與前額皮質活動減少有關。
It's possible that the brain circuits that prevent emotions from overwhelming your ability to make decisions.
大腦中防止情緒壓倒你做決定的能力的回路是可能的。
Don't fully develop until you're a little older.
長大一點才會完全發育。
Some researchers think that the definition of adulthood should really be when you've got more control over these kinds of emotional responses.
一些研究人員認為，成年的定義應該是當你對這些情緒有更多的控制反應。
Which for some people might be 22.
有些人可能是22歲。
But, for others, could be much later.
但對其他人來說，可能要晚得多。
As you get older and learn new skills you're strengthening connections and physically rearranging things.
隨著年齡的增長和新技能的掌握，你會加強人際關系，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，即使你已經超過18歲，還沒覺得自己像個真正的成年人。
Take heart that your brain has more changing to do.
振作起來，你的大腦有更多的變化要做。
Thanks for watching this episode of SciShow Psych
感謝收看本期心理科學秀！
If you want to learn more about the practical side of adulting.
如果你想了解更多關于成人的實用內容。
Go check out how to adult at youtube.com/learnhowtoadult
去youtube.com/learnhowtoadult觀看看我們的節目
Which has videos about everything from doing taxes to picking wine.
里面各種視頻，應有盡有。
