What percentage of your brain do you use? - Richard E. Cytowic

譯者: Regina Chu 審譯者: Dong Mao

An enduring myth says we use only 10% of our brain,

有個歷久不衰的傳說

說我們只用了大腦的 10%

the other 90% standing idly by for spare capacity.

其餘的 90% 閒著備用

Hucksters promised to unlock that hidden potential

賣膏藥的人保證你能釋放潛能

with methods "based on neuroscience,"

用「有神經科學根據」的方法

but all they really unlock is your wallet.

但實際只釋放了你的錢包

Two-thirds of the public and nearly half of science teachers

三分之二的大眾

和近半的科學老師

mistakenly believe the 10% myth.

誤信這 10% 的傳說

In the 1890s, William James,

1890 年代，威廉‧詹姆士

the father of American psychology, said,

美國心理學之父

"Most of us do not meet our mental potential."

說：「大部分的人都沒有充分發揮

他們的心智潛能」

James meant this as a challenge,

詹姆士意指這是一個挑戰

not an indictment of scant brain usage.

而不是指控很少用腦

But the misunderstanding stuck.

但這誤解延續至今

還有，科學家長久以來

Also, scientists couldn't figure out for a long time

都搞不清楚

the purpose of our massive frontal lobes

我們巨大的額葉

or broad areas of the parietal lobe.

或大面積的頂葉的功能

Damage didn't cause motor or sensory deficits,

損傷並不會造成運動或感覺障礙

so authorities concluded they didn't do anything.

所以科學家斷定它們沒用

For decades, these parts were called silent areas,

數十年來，這些部分

被稱為 「寂靜區域」

their function elusive.

他們的功能令人費解

We've since learned that they underscore

我們後來得知它們強調

executive and integrative ability,

執行及整合能力

without which, we would hardly be human.

沒有它們，我們稱不上是人類

They are crucial to abstract reasoning,

它們對於抽像推理

planning, weighing decisions

計畫

衡量決定

and flexibly adapting to circumstances.

及對各種情況的適應力非常重要

The idea that 9/10 of your brain sits idly by in your skull

你的大腦十分之九

在顱腔內閒著的這個想法

looks silly when we calculate how the brain uses energy.

看起來很蠢，如果我們計算 腦部如何使用能量

齧齒類及犬類的腦消耗

Rodent and canine brains

consume 5% of total body energy.

身體總能量的 5%

Monkey brains use 10%.

猴子的腦使用 10%

An adult human brain,

一個成年人的腦

which accounts for only 2% of the body's mass,

只占身體總質量的 2%

consumes 20% of daily glucose burned.

卻消耗 20% 每日燃燒葡萄糖量

In children, that figure is 50%,

而孩童，這數字是 50%

and in infants, 60%.

而在嬰兒，60%

This is far more than expected for their relative brain sizes,

這比預期高出許多

與他們相對的腦容量而言

which scale in proportion to body size.

而腦容量與身體大小成正比

Human ones weigh 1.5 kilograms,

人類的腦重 1.5 公斤

elephant brains 5 kg,

大象的腦 5 公斤

and whale brains 9 kg,

而鯨魚的腦 9 公斤

yet on a per weight basis,

而以重量比來看

humans pack in more neurons than any other species.

人類裝了更多的神經元

比其他物種都多

This dense packing is what makes us so smart.

這種高密度填充 就是我們如此聰明的原因

There is a trade-off between body size

靈長類動物在身體大小

and the number of neurons a primate,

及能維持多少神經元之間

including us, can sustain.

必須取得平衡，這也包括人類

A 25 kg ape has to eat 8 hours a day

一隻 25 公斤的猩猩每天要吃 8 小時

to uphold a brain with 53 billion neurons.

以維持牠腦內五百三十億個神經元

The invention of cooking,

而發明烹調法

one and half million years ago,

在 150 萬年前

gave us a huge advantage.

給了我們巨大的優勢

Cooked food is rendered soft and predigested

煮熟的食物使之變軟而且已在身體外

outside of the body.

先消化過了

Our guts more easily absorb its energy.

我們的腸胃更容易吸收它的能量

Cooking frees up time and provides more energy

煮食釋放出時間

及提供更多能量

than if we ate food stuffs raw

比之於我們吃生食

and so we can sustain brains

所以我們才能維持腦內

with 86 billion densely packed neurons.

八百六十億緊密填充的神經元

比猩猩還多 40%

40% more than the ape.

Here's how it works.

這是它運作的方式

Half the calories a brain burns

半數大腦燃燒的卡路里

go towards simply keeping the structure intact

拿去維持結構不變

by pumping sodium and potassium ions

由主動運輸鈉鉀離子

across membranes to maintain an electrical charge.

通過細胞膜以維持電荷來達成

To do this, the brain has to be an energy hog.

要這樣做，大腦必須 是隻貪吃能源的豬

It consumes an astounding

它每分鐘要消耗驚人的 3.4 x 10^21 個三磷酸腺苷分子

3.4 x 10^21 ATP molecules per minute,

ATP being the coal of the body's furnace.

三磷酸腺苷是身體能源火爐的煤炭

The high cost of maintaining resting potentials

要維持靜止電位的高代價

in all 86 billion neurons

在全部八百六十億神經元中

means that little energy is left

意指只有所剩無幾的能量

to propel signals down axons and across synapses,

能輸出信號到軸突及穿越突觸

the nerve discharges that actually get things done.

造成神經放電，也就是任務完成

Even if only a tiny percentage of neurons

即使只有極少百分比的神經元

fired in a given region at any one time,

在某個時段某個區域被激發

the energy burden of generating spikes over the entire brain

其在整個大腦產生電衝動

所需的能量負擔

would be unsustainable.

也是無法持續的

這是節能要起作用的地方

Here's where energy efficiency comes in.

Letting just a small proportion of cells signal at any one time,

讓只有一小部分的細胞

在任何一段時間發送信號

known as sparse coding,

這被稱為稀疏編碼

uses the least energy,

用最少的能量

but carries the most information.

但傳遞最多的訊息

Because the small number of signals

因為這少數的信號

have thousands of possible paths by which to distribute themselves.

可以用數千種路徑

來傳遞

A drawback of sparse coding within a huge number of neurons

在這麼大量的神經元內

稀疏編碼有個缺點

is its cost.

就是成本很高

Worse, if a big proportion of cells never fire,

更糟的是，如果一大部分的 細胞從未被激發

then they are superfluous

那他們就是多餘的

and evolution should have jettisoned them long ago.

演化早該在很久以前就把他們拋棄

The solution is to find the optimum proportion of cells

解決的方法是找到

在某時刻內，腦內有多少

that the brain can have active at once.

活躍的細胞的最佳比例

For maximum efficiency,

要獲得最大的效率

between 1% and 16% of cells should be active at any given moment.

應該要有介於 1% 到 16% 間的細胞

在任一時刻處在活躍狀態

This is the energy limit we have to live with

這是能量的限制

我們必須與之共存

in order to be conscious at all.

這是為了能保持有意識狀態

The need to conserve resources

腦部需要節約資源

is the reason most of the brain's operations

正是絕大部分的腦部運作

must happen outside of consciousness.

都必須發生在意識以外的主要原因

It's why multitasking is a fool's errand.

這就是為什麼多工只是徒勞無功

We simply lack the energy to do two things at once,

我們就是沒有能量同時做兩件事

let alone three or five.

就別提三件或五件事了

When we try, we do each task less well

當我們試著多工，我們每件事的成效

than if we had given it our full attention.

都比只專心做一件事要差

The numbers are against us.

數字對我們不利

你的大腦已經很聰明，威力強大

Your brain is already smart and powerful.

So powerful that it needs a lot of power to stay powerful.

如此強大，它需要很多能量

以保持強大

And so smart

而且是如此聰明

that it has built in an energy-efficiency plan.

它已經內建了一個節能計畫

So don't let a fraudulent myth make you guilty

所以不要讓一個不實的傳說

讓你對

about your supposedly lazy brain.

本應懶惰的大腦感到愧疚

Guilt would be a waste of energy.

愧疚會浪費能量

After all this,

在這長篇大論之後

don't you realize it's dumb to waste mental energy?

你難道還不明瞭浪費心智能量

是件很蠢的事？

You have billions of power-hungry neurons to maintain.

你有數十億

餓的要命的神經元要維持

So hop to it!

所以快點上工吧！