until their joints make noises? Humans are weird. Why do we do this?!

直到聽到喀喀喀的聲音才可罷休？人類實在很奇怪。為什麼我們會有這些行為？

Yo nail-biters, Trace here for DNews, what's up? Pia Hansen sent us a good question recently,

唷！咬指甲的人！我是 Dnews 的 Trace，你們好嗎？最近，Pia Hansen問我們一個很好的問題

about why people develop weird habits like nail-biting and knuckle-popping.

為什麼人們會有奇怪的習慣，像是咬指甲和折關節？

So, I looked into it!

所以，我對這問題做了調查！

Firstly, nail biting is a bad habit, but unless it becomes extreme, it's probably not harmful.

第一點，咬指甲是一個不好的習慣。除非，你們過度的咬指甲，要不然這習慣大概也不會有什麼傷害

If it's a regular, pathological thing, it can become what's called "pathological grooming."

如果這病態的習慣只是偶然出現，就稱為「過度性整理儀容」

Which is uncontrolled, extreme grooming behaviors, like nail biting, skin picking, or hair pulling.

這是無法控制的，強迫性的整理行為，就像是咬指甲、摳自己的皮膚、或是拉頭髮

On the other hand, or… the OTHER hand… Scientists only recently learned

此外，另一方面，科學家最近研究出

what cracking your knuckles is actually DOING inside your fingers. The sound is caused by "cavitation via tribonucleation…"

你們折手指的聲音是由手的關節內發出，這個聲音是關節摩擦生核而發出的氣穴現象

Basically, gas dissolved in the fluid between your joints forms a bubble,

基本上，溶解在關節滑液中的氣體會析出形成小氣泡

and the sound is caused when the bubble FORMS, not pops.

而這些小氣泡融合成大氣泡則發出聲響，不是憑空冒出的

And though it's weird lookin', scientists don't think it's actually harmful.

雖然這行為難以解釋。但，科學家們認為這對身體沒有實質的傷害

But the underlying question, as I see it, is why we have ANY HABIT at all.

但，我想主要的問題是，究竟為什麼我們會有這些習慣

Neuroscientists have tried to figure out where habits come from, and traced the path back to a part of the brain

神經學家曾想要找出這些習慣的原因，因而追溯到人類的腦部區塊：

called the basal ganglia -- it's connected with coordination and movement.

稱之為基底神經節系統－－負責統合我們的動作和控制身體

It's likely not the only system involved, because habits are complex behaviors,

但，他似乎不是唯一牽扯到的身體器官，因為習慣是複雜的行為表現

but numerous studies, keep coming back to the ol' BG.

但，許多研究仍無法擺脫以前的研究

From a psychological perspective, a habit needs a few things to form: a trigger, an action, and a reward.

由心理學來看，一個習慣是由幾個原因形成的：一個觸發點、一個行動、和一個獎勵

Together, they form a habit-loop. The habit loop is built on the

這三個過程則會形成一個習慣迴圈。這樣的習慣迴圈是基於

idea that at some point, you got a reward for doing the action in the first place.

你們一開始做了某種行為，而得到獎賞

For example: let's say you have a hangnail, it hurts… you pick at it, but it just hurts more…

例如：這樣說好了，你們有指甲倒刺（指甲周圍的皮膚出現乾燥，掀起一角的皮膚），痛不欲生的。你們拔他，只是更痛而已

so you pull it out with your teeth! Boom no more hangnail, no more pain! Trigger, action, reward!

所以，你們用牙齒把他拉出來！砰！不再有指甲倒刺，不再痛苦！這就是所謂的觸發點、行動、獎勵！

Simple behavioral training. Finger cracking could be the same, though

簡單的行為養成。折手指也是一樣的道理。雖然

the reward is somewhat more nebulous… Dr. Rachel Vreeman told NBC News, it could just

這折手指的獎勵令人難以理解‧‧‧但，Rachel Vreeman博士在NBC News指出，折手指的獎勵只是會

be a "physical release!" Maybe it just feels nicer? Or maybe you just like the noise!

讓人感到「身體的釋放」！可能這麼做能感到舒服？也可能你們只是喜歡這吵雜聲而已吧！

How that one moment of pleasure turns into a habit is through repetition.

但，為什麼這樣反覆享受一個美好的時刻，能造就一個永久的習慣

If you bite a hangnail enough times, you'll stop thinking about biting your hangnails, and then you have a habit.

如果你們咬掉指甲的倒刺，一旦多次下來之後，你們這樣的習慣動作就會自然而然的形成

Our brain is lazy, so if we can offload a task to our subconscious, we're going to that!

我們的腦袋是遲鈍的。所以，如果我們過度的運用我們的下意識

And once a habit is established, we stop thinking about it. Like, literally,

一旦這樣的習慣模式被建立起來，我們就不再經過大腦思考而行動。毫無疑問的

we stop sending the behavioral activity from the basal ganglia to the prefrontal cortex. The PFC is where we make decisions…

我們無須再靠基底神經節系統與前額葉皮質的系統給予動作的指示。這個前額葉皮質系統是來協助我們擬定計畫與執行決策

so if we're not engaging that part of our brain, we're literally not "thinking about it" before we do it.

所以，在我們做動作之前，我們完全不再依靠他們和「思考我們的行為」

Commonly, this can take from 15 to 254 DAYS of training.

普遍而言，這樣的習慣養成大概需要15到254天

Most of the time, if a habit isn't physically harmful, it’s just considered a bad social habit,

通常，一個習慣不會帶給身體有所傷害，只被視為一個社會所不認同的習慣

but if a habit creates open wounds or sores, begins wearing down your teeth,

但，如果一個習慣會造成開放性的咬傷或潰瘍，而且間接性的使得牙齒磨損

someone is literally pulling their hair out… doctors can diagnose it as a psychological condition.

像是有人會拔掉他們的頭髮‧‧‧醫生診斷這樣的行為為一種心理問題

This means your brain has likely paired nail-biting, for example, with relief of anxiety or stress.

意思是你們的腦袋會認為咬指甲這件事是可以減輕焦慮與不安

Damaging, compulsive nail-biting is called onychophagia,

這種衝動性和強迫性的咬指甲行為稱之為咬指甲癖（強迫性拔掉指甲）

and it's referred to as a "stress removal habit" by the Indian Journal of Dental Research

在印度牙科研究文獻中被稱為「減輕壓力的嗜好」

and appears on the spectrum of Obsessive Compulsive Disorders in the DSM-V.

也在精神疾病診斷準則手冊第五版中稱為強迫症（OCD）

Why some people pair stress relief with a habit isn't entirely clear.

但，為什麼有些人的習慣與紓壓並無明顯關係

But a 1970s twin study found there may be a genetic link.

在1970年，從雙胞胎案例中，研究出此習慣與基因的關聯性

Nail biting was practiced by nearly one-third of the 338 pairs of twins, and more in girls than boys;

調查338對雙胞胎中，高達1/3女性咬指甲比率則多過於男性

and it was more common in twins who came from the same zygote!

而同卵雙胞胎咬指甲的疾病會更普遍

Habits CAN be broken, but it takes work! You simply have to remind yourself to run your actions BACK through your prefrontal cortex!

習慣可以抑制，但，需要下苦工！簡單而言，你們必須要運用大腦前額葉來抑制自己的行動

That's why your mom put bandages or hot sauce on your fingers to keep you from biting your nails --

這就是為什麼你們的母親會用繃帶綁住手指或用辣椒水塗抹手指頭，來防止你們咬指甲

it reminded your brain, hey, pay attention, you could kick this habit! I don't bite my nails, but I DO I shake my leg a lot, like… a LOT a lot.

這警惕你們的腦袋要注意這樣的行為，而學習抑制掉這習慣！我不咬指甲，但，我的確愛抖腳‧‧‧非常非常愛

But why do we fidget? What's up with that? Luckily, some handsome devil looked into it over here.

為什麼我們會這樣坐立不安？是為什麼？幸運地，幾位英明的老兄深入研究這個問題

A 130 years ago, people fidgeted. It's definitely not caused by over-caffeniated, ADHD-prone, coddled millennials.

在130年前，人們坐立難安，不是因過多的咖啡因或是研究多時的專注力缺陷過動傾向症（Attention-deficit hyperactivity disorder）相關

Instead, fidgeting seems to be part of human nature. Are you a nail-biter? A finger-popper? Do you have tips to stop?

這樣的坐立不安反而是與人類的天性相關。你們喜歡咬指甲嗎？你們愛折手指嗎？你們有什麼方式可以戒掉這些壞習慣？

Share 'em here and ask us more science questions with the hashtag AskDNews! Thank you for your watching. See you next time.

在底下跟我們分享，也可以問我們其他問題，記得標記＃AskDNews。謝謝你們的收看。下次見