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You're standing at the ready inside the goal.
你正站在球門內準備好了
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When suddenly, you feel an intense itch on the back of your head.
突然,後腦感到一陣強烈的癢
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We've all experienced the annoyance of an inconvenient itch,
我們都曾因為當下不方便處理的癢而感到煩躁不已
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but have you ever pondered why we itch in the first place?
但首先,你有仔細想過為何我們會覺得癢嗎?
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The average person experiences dozens of individual itches each day.
每天人們平均會感受到數十次癢的感覺
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They can be triggered by all sorts of things,
許多事物都能觸發癢的感覺
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including allergic reactions,
包括過敏反應
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dryness,
乾燥
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and even some diseases.
甚至是某些疾病
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And then there are the mysterious ones that pop up for no reason at all,
另外,還有一種神祕的情況是它毫無原因的突然出現
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or just from talking about itching.
或僅僅是談論癢也能觸發癢的感覺
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You're scratching your head right now, aren't you?
你現在正在抓你的頭,沒錯吧?
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Anyhow, let's take one of the most common sources: bug bites.
無論如何,我們先從最常見的觸發原因之一開始探討:昆蟲咬傷
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When a mosquito bites you,
當蚊子咬你時
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it releases a compound into your body called an anticoagulant
牠的口器會釋放名為「抗凝血劑」的混和物到你的身體中
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that prevents your blood from clotting.
避免你的血液凝結
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That compound, which we're mildly allergic to,
由於我們的身體對這個混和物輕微過敏
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triggers the release of histamine,
因此它會觸發組織胺的釋放
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a chemical that makes our capillaries swell.
組織胺是一種會讓我們的微血管膨脹的化學物質
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This enables increased blood flow,
微血管膨脹使得血流增加
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which helpfully accelerates the body's immune response
會加速當身體察覺到威脅時
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to this perceived threat.
所做出的免疫反應
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That explains the swelling,
這解釋了蚊子咬的地方會腫脹的原因
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and it's the same reason pollen can make your eyes puff up.
而花粉會讓你的眼周腫脹也是相同的原因
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Histamine also activates the nerves involved in itching,
組織胺也會刺激癢覺相關的神經
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which is why bug bites make you scratch.
這也是為什麼蟲咬會讓你想抓癢
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But the itchy sensation itself isn't yet fully understood.
但是目前癢覺本身還沒被完全理解
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In fact, much of what we do know
事實上,我們所知很多有關癢覺的知識
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comes from studying the mechanics of itching in mice.
都來自於老鼠體內癢覺機制的研究
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Researchers have discovered that itch signals in their skin
研究人員發現老鼠皮膚中的癢覺信號
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are transmitted via a subclass of the nerves that are associated with pain.
是從掌管痛覺相關的子神經轉換而來
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These dedicated nerves produce a molecule called natriuretic polypetide B,
這些專門的神經產生了一種叫"Natriuretic polypetide B"的分子結構
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which triggers a signal that's carried up the spinal cord to the brain,
這個分子會觸發訊號,經由脊髓傳到大腦中
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where it creates the feeling of an itch.
因此大腦就會產生癢的感覺
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When we scratch, the action of our fingernails on the skin
當我們搔抓時,指甲在皮膚上的動作
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causes a low level pain signal that overrides the itching sensation.
會產生可以壓制癢覺的低程度痛覺訊號
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It's almost like a distraction, which creates the sensation of relief.
它就像是干擾一樣,使得癢的感覺得到舒緩
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But is there actually an evolutionary purpose to the itch,
然而,癢這件事和演化目的有關嗎?
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or is it simply there to annoy us?
還是它僅僅是一個讓我們煩躁的現象呢?
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The leading theory is that our skin has evolved to be acutely aware of touch
目前主流的理論是我們的皮膚已經進化到可敏銳地感知觸覺
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so that we're equipped to deal with risks from the outside world.
使得我們能夠處理來自外界的危險
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Think about it.
試著想想看
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Our automatic scratching response would dislodge anything harmful
我們對癢的自動搔抓反應可以驅逐任何可能
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that's potentially lurking on our skin,
對我們的皮膚有潛在傷害的事物
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like a harmful sting,
像是傷人的刺
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a biting insect,
正在咬我們的昆蟲
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or the tendrils of a poisonous plant.
或是有毒植物的卷鬚
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This might explain why we don't feel itching inside our bodies,
這或許解釋了為何我們不覺得身體內部會癢
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like in our intestines,
像是我們的腸子
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which is safe from these external threats,
它們不會受到這些外在威脅
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though imagine how maddening that would be.
想想看,如果腸子會受到這些外在威脅,那會是多讓人惱怒的事情
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In some people, glitches in the pathways responsible for all of this
對某些人來說,負責傳送感覺的神經路徑上的干擾
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can cause excessive itching that can actually harm their health.
可能會導致過度搔癢進而影響健康
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One extreme example is a psychological condition called delusory parasitosis
其中一個極端的例子就是名為「寄生蟲妄想症」的心理現象
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where people believe their bodies are infested with mites or fleas
它會讓人覺得他們的身體佈滿大量的蟎蟲和跳蚤
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scurrying over and under their skin,
並且在皮膚底下亂竄
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making them itch incessantly.
讓他們不斷的發癢
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Another phenomenon called phantom itching
另外一種現象則稱為「幻肢搔癢」
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can occur in patients who've had amputations.
這個現象常發生在曾經做過截肢手術的病人身上
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Because this injury has so severely damaged the nervous system,
由於他們所受的傷害對該神經系統造成嚴重損壞
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it confuses the body's normal nerve signaling
使得身體中正常的神經訊號產生混淆
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and creates sensations in limbs that are no longer there.
並讓早已不存在的肢幹產生感覺
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Doctors are now finding ways to treat these itching anomalies.
醫生們也在尋找這種異常癢覺的治療方法
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In amputees, mirrors are used to reflect the remaining limb,
對於已截肢的人,會利用鏡子將其仍存在的肢幹反射到已被截肢的那側
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which the patient scratches.
並且搔抓那仍存在的肢幹
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That creates an illusion that tricks the brain
那樣做產生了欺騙大腦的幻象
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into thinking the imaginary itch has been satisfied.
讓大腦認為幻肢的癢覺已經滿足了
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Oddly enough, that actually works.
說也奇怪,這個方法確實有用
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Researchers are also searching for the genes involved in itching
研究員們也正在研究和癢覺有關的基因
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and developing treatments to try and block the pathway of an itch
並發展在某些極端狀況下阻止癢覺
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in extreme cases.
的治療方法
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If having an unscratchable itch feels like your own personal hell,
如果你認為不能抓的癢是地獄的話
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Dante agreed.
但丁是同意這個觀點的
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The Italian poet wrote about a section of hell
這位義大利詩人描寫的其中一個地獄類型
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where people were punished by being left in pits to itch for all eternity.
就是人們被留在一個深坑內受著永恆的搔癢作為處罰