a ping-pong match in orbit around a black hole,

一場在黑洞旁軌道上的乒乓球賽

a dolphin balancing a pineapple.

一隻海豚試圖平衡一顆鳳梨

You probably haven't actually seen any of these things,

你也許從沒看過剛剛的任何一樣東西

but you could imagine them instantly.

但你可以立刻想像出他們

How does your brain produce an image of something you've never seen?

你的大腦是怎麼產生出一張你從沒看過東西的畫面呢？

That may not seem hard,

那似乎不是太困難

but that's only because we're so used to doing it.

但那只是因為我們非常習慣於這件事了

It turns out that this is actually a complex problem

這實際上是個複雜的問題

that requires sophisticated coordination inside your brain.

你的大腦中需要複雜的協調合作

That's because to create these new, weird images,

創造出這些新奇的畫面

your brain takes familiar pieces and assembles them in new ways,

你的大腦需要取出相近的片段 再將他們用不同的方式組合起來

like a collage made from fragments of photos.

就像利用各部份相片完成一幅拼貼畫作

The brain has to juggle a sea of thousands of electrical signals

大腦必須應付海一般成千上萬的電子訊號

getting them all to their destination at precisely the right time.

並在準確的時間點將他們放到各自的目的地

When you look at an object,

當你看著一樣東西

thousands of neurons in your posterior cortex fire.

後皮質裡上千個神經元正受到激發

These neurons encode various characteristics of the object:

這些神經元編碼出各種關於這樣東西的特性：

spiky, fruit, brown, green, and yellow.

帶刺的、水果、咖啡色、綠色和黃色

This synchronous firing strengthens the connections between that set of neurons,

這個同步激發使的那些神經元彼此間的連結更強

linking them together into what's known as a neuronal ensemble,

讓他們結成了我們所知道的神經元集群

in this case the one for pineapple.

鳳梨這個例子中

In neuroscience, this is called the Hebbian principle,

在神經科學裡稱之為赫布理論

neurons that fire together wire together.

那些共同受到激發有所連結的神經元

If you try to imagine a pineapple later,

假設過了一下子，你試圖去想像一個鳳梨

the whole ensemble will light up, assembling a complete mental image.

整個集群會亮起來並組合出一個完整的心理意象

Dolphins are encoded by a different neuronal ensemble.

海豚則會由不同神經元集群來編碼出來

In fact, every object that you've seen

事實上，你看到的每一樣物品

is encoded by a neuronal ensemble associated with it,

皆由一個神經元集群來產生與它相關的編碼

the neurons wired together by that synchronized firing.

藉由同時受到激發而使那些神經元連結在一起

But this principle doesn't explain the infinite number of objects

然而這個理論並無法解釋我們如何想像出無限多種物品

that we can conjure up in our imaginations without ever seeing them.

即使我們從未見過那些東西

The neuronal ensemble for a dolphin balancing a pineapple doesn't exist.

"一隻海豚試圖平衡鳳梨"這樣的神經元集群並不存在

So how come you can imagine it anyway?

那麼，你為什麼能想像這個畫面呢？

One hypothesis, called the Mental Synthesis Theory,

有一個假說叫"心理合成理論"

says that, again, timing is key.

又再次重申了關鍵在於時間點

If the neuronal ensembles for the dolphin and pineapple

如果海豚與鳳梨的兩個神經元集群

are activated at the same time,

同時受被激發

we can perceive the two separate objects as a single image.

我們便能在同一畫面中感知到兩個不同物品

But something in your brain has to coordinate that firing.

但必須由你大腦中的某樣東西來協調這樣的激發

One plausible candidate is the prefrontal cortex,

最有可能的角色就是前額皮質

which is involved in all complex cognitive functions.

因為它幾乎參與了所有複雜的認知行為

Prefrontal cortex neurons are connected to the posterior cortex

前額皮質中的神經元與後皮質連結在一起

by long, spindly cell extensions called neural fibers.

藉由長且纖細的組織延伸 稱之為神經纖維

The mental synthesis theory proposes that like a puppeteer pulling the strings,

心理合成理論認為如同木偶師操縱著繩子

the prefrontal cortex neurons send electrical signals

前額皮質神經元傳送出電子訊號

down these neural fibers

沿著那些神經纖維

to multiple ensembles in the posterior cortex.

抵達數個後皮質中的神經元集群

This activates them in unison.

使得他們行為一致

If the neuronal ensembles are turned on at the same time,

若那些神經元群集能夠在同時受到激發

you experience the composite image just as if you'd actually seen it.

你就如真的看見一般想像出合成畫面

This conscious purposeful synchronization

這個感知有目的的藉由前額皮質

of different neuronal ensembles by the prefrontal cortex

使得數個神經元集群達成同步

is called mental synthesis.

稱之為心理合成

In order for mental sythesis to work,

為了使它順利運作

signals would have to arrive at both neuronal ensembles at the same time.

訊號必須同時抵達神經元集群

The problem is that some neurons

會出現的問題是

are much farther away from the prefrontal cortex than others.

有些神經元比其他前額皮質中的神經元遠的多

If the signals travel down both fibers at the same rate,

如果訊號以同樣速度在神經纖維中傳輸

they'd arrive out of sync.

他們並無法同時到達

You can't change the length of the connections,

你無法改變連結的長度

but your brain, especially as it develops in childhood,

但你的大腦，特別是在孩童發展階段

does have a way to change the conduction velocity.

的確有辦法改變傳導速度

Neural fibers are wrapped in a fatty substance called myelin.

神經纖維外層包裹著富含脂肪的物質稱為髓鞘

Myelin is an insulator

髓鞘是一種絕緣體

and speeds up the electrical signals zipping down the nerve fiber.

可以加快電子訊號在神經纖維中的傳送速度

Some neural fibers have as many as 100 layers of myelin.

有些神經纖維外甚至包著100層之多的髓鞘

Others only have a few.

其他的則數量較少

And fibers with thicker layers of myelin

那些包裹著較厚髓鞘層的神經纖維

can conduct signals 100 times faster or more

相較於沒那麼厚的神經纖維

than those with thinner ones.

傳導速度可達到或超過100倍

Some scientists now think that this difference in myelination

部份科學家開始認為這些髓鞘層的厚薄程度

could be the key to uniform conduction time in the brain,

也許就是平衡大腦中傳導時間的關鍵

and consequently, to our mental synthesis ability.

所以，對於我們心理合成的能力

A lot of this myelination happens in childhood,

大部分的髓鞘生長於孩童時期

so from an early age,

因此小時候

our vibrant imaginations may have a lot to do with building up brains

我們活躍的想像力對於建構大腦有很大的作用

whose carefully myelinated connections

有著髓鞘良好發展的連結

can craft creative symphonies throughout our lives.

能作出富有創造力的生命樂章