But instead of the sound of silence, you hear a constant ringing — even though there's nothing making any noise.

但你聽到的不是一片寂靜，而是不停的鳴響 — 即使沒有東西製造任何噪音。

What you're experiencing is called tinnitus, the perception of a noise like ringing, buzzing, hissing or clicking that occurs without any external source of sound.

你所感受到的就是所謂的耳鳴，察覺到像鳴響聲、嘈雜聲、嘶嘶聲，或卡嗒聲之類的噪音，卻不是來自任何外部的聲源。

Tinnitus has been bothering humanity since Ancient Babylon, plaguing everyone from Leonardo da Vinci to Charles Darwin.

打從古巴比倫時代開始，耳鳴就開始煩擾人類了，從達文西到達爾文都是受害者。

Today, roughly one in seven people worldwide experiences this auditory sensation.

現今，全世界約七人之中就有一人正在經歷這種聽覺感知。

So where does this persistent sound come from?

所以，這種持續的聲音來自何方？

When you normally hear something, sound waves hit various areas of your ear, creating vibrations that displace fluid inside the cochlea.

你通常會聽到聲音是因為聲波擊中你耳內的各個區域，造成震動，使耳蝸中的液體移動。

If the vibrations are large enough, they elicit a chemical response that transforms them into bioelectrical signals.

如果震動夠大，便會引發化學反應，將震動轉變成為生物電訊號。

These nerve impulses are then relayed through the hearing pathway to the brain, where they result in the sounds we perceive.

接著這些神經衝動 (脈衝) 會透過聽覺路徑傳遞到腦部，在腦部就會產生我們察覺到的聲音。

However, in the vast majority of tinnitus cases, the nerve signals that produce these mysterious sounds don't travel through your ear at all.

然而，在大部分的耳鳴案例中，產生這些神秘聲音的神經訊號完全不會經過你的耳朵。

Instead, they're generated internally, by your own central nervous system.

反之，它們是由你自己體內的中樞神經系統生成的。

Under usual circumstances, these self-produced signals are an essential part of hearing.

在一般的情況下，這些自行產生的訊號是聽力很重要的一部分。

All mammals demonstrate on-going neural activity throughout their hearing pathways.

所有哺乳類動物的聽覺路徑上都會持續有神經波動。

When there are no sounds present, this activity is at a baseline that establishes your neural code for silence.

當沒有聲音出現時，這種波動就處於基線，而這代表寂靜的神經編碼。

When a sound does appear, this activity changes, allowing the brain to distinguish between silence and sound.

一旦出現聲音，這種波動就會改變，讓腦部可以區別出寂靜和聲音的差別。

But the auditory system's health can affect this background signal.

但聽覺系統的健康有可能會影響到這種背景訊號。

Loud noises, diseases, toxins, and even natural aging can damage your cochlear cells.

巨大的聲音、疾病、毒素，甚至自然老化，都有可能損害你的耳蝸細胞。

Some of these may heal in a matter of hours.

有些細胞在幾個小時內就會癒合。

However, if enough cells die, either over time or all at once, the auditory system becomes less sensitive.

但是，如果太多細胞死亡，不論是逐漸死亡，或是一次同時死亡，聽覺系統都會變得比較不敏感。

With fewer cochlear cells relaying information, incoming sounds generate weaker nerve signals.

當傳遞資訊的耳蝸細胞減少，進來的聲音所產生的神經訊號就會比較弱。

And many environmental sounds can be lost completely.

此外，許多環境聲音還會完全消失。

To compensate, your brain devotes more energy to monitoring the hearing pathway.

為了補償這部分，你的腦部就會用更多能量來監視聽覺路徑。

Just like you might adjust the knobs of a radio, the brain modifies neural activity while also tweaking the tuning knob to get a clearer signal.

就像你有可能會去調整收音機的旋鈕，腦部也會修改神經活動，同時微調旋鈕，以取得更清楚的訊號。

Increasing this background neural activity is intended to help you process weak auditory inputs.

增加這種背景神經活動的目的是要協助你處理較弱的聽覺輸入。

But it can also modify your baseline for silence — such that a lack of sound no longer sounds silent at all.

但這麼做也有可能會修改你的寂靜基線 — 導致「沒有聲音」聽起來完全不像是寂靜的狀態。

This is called subjective tinnitus, and it accounts for the vast majority of tinnitus cases.

這就是所謂的「自覺性耳鳴」，而大部分的耳鳴案例都屬於這一種。

Subjective tinnitus is a symptom associated with practically every known ear disorder, but it isn't necessarily a bad thing.

幾乎所有已知的耳朵相關疾病都會有自覺性耳鳴的症狀，但那不見得不好。

While its appearance can be surprising, subjective tinnitus has no inherently negative consequences.

雖然自覺性耳鳴的出現會讓人感到出人意料，但它本身並沒有負面的影響。

But for some, tinnitus episodes can trigger traumatic memories or otherwise distressing feelings, which increase the sound's intrusiveness.

但對某些人來說，耳鳴發作會觸發創傷性的記憶或讓人苦惱的感受，因而增加聲音的煩擾程度。

This psychological loop often leads to what's known as "bothersome tinnitus," a condition that can exacerbate the symptoms of PTSD, insomnia, anxiety, and depression.

這種心理迴圈會導致一般所知的「困擾性耳鳴」，這種病症會讓創傷後壓力症候群、失眠、焦慮，及憂鬱的症狀加劇。

There's no known cure for subjective tinnitus.

自覺性耳鳴目前沒有已知的療法。

So the most important thing doctors can do is help people understand this auditory event, and develop neutral associations with these often-distressing sounds.

所以，醫生能做的最重要的事，就是協助患者了解這種聽覺狀況，並針對這些讓人煩擾的聲音發展出有中和作用的關聯性。

For example, sound therapy uses noises like rain, birdsong, or music to mask tinnitus and reduce stress.

比如，聲音治療會使用聲音，如雨聲、鳥鳴、音樂，來遮蔽耳鳴並減少壓力。

One form, called informational masking, uses soothing, complex auditory signals that distract the brain from the tinnitus sound.

有一種形式叫做「資訊遮蔽」，用讓人寬心、複雜的聲音訊號來讓腦部分心，不去注意耳鳴聲。

Another, called energetic masking, uses sounds with the same frequency as the patient's tinnitus to occupy the neurons that would otherwise deliver the tinnitus signal.

還有一種形式叫作「能量遮蔽」，採用和患者耳鳴同頻率的聲音，來佔據本來會傳遞耳鳴訊號的神經元。

Practiced alongside counseling, these interventions allow people to re-evaluate their relationship with tinnitus.

這些介入治療方式再搭配諮詢，能讓患者重新評估他們和耳鳴的關係。

Losing the sound of silence can be troubling to say the least.

再怎麼說，失去寂靜的感覺都會讓人感到煩擾。

Tinnitus reveals that your brain is constantly analyzing the world around you, even as it fails to filter its own internal noise.

有耳鳴就表示，即使你的腦部無法過濾掉它自己的內部噪音時，也仍然不斷地分析你周遭的世界。

In a sense, experiencing tinnitus is like eavesdropping on your brain talking to itself — though it may not be a conversation you want to hear.

在某種層面上，聽到耳鳴就像是偷聽到你的腦部在跟它自己說話 - 不過那可能不是你想要聽見的對話。

As mentioned in this video, tinnitus can be particularly difficult for those struggling with PTSD, but what exactly is this disorder?

在這支影片有提到，耳鳴對於那些患有創傷後壓力症候群的人特別困擾，但是這種疾病到底是什麼呢？

And what steps can be taken to help those suffering from it?

然而，可以採取什麼步驟來幫助那些受苦的人？

Learn more with this video, or check out this video for advice on coping with insomnia.

觀看這部影片了解更多，或是觀看右方的影片得知有關解決失眠的建議。