How fast is the speed of thought? - Seena Mathew

譯者: Lilian Chiu 審譯者: Helen Chang

Your mortal enemy has captured you and hooked you up to a bizarre experiment.

你的死敵抓到你，

把你綁起來做一項怪異的實驗。

He’s extended your nervous system with one very long neuron

他用非常長的神經元 延伸你的神經系統

to a target about 70 meters away.

到七十公尺外的目標。

At some point, he’s going to fire an arrow.

在某個時點，他會射出一支箭。

If you can then think a thought to the target before the arrow hits it,

如果你能在箭射中目標之前 把一個思想送到目標，

he’ll let you go.

他就會放你走。

So who wins that race?

那麼，誰會贏得比賽？

In order to answer, we have to examine the hardware of thought: neurons.

為了解答這個問題， 我們必須先探究思想的硬體：

神經元。

The human brain has about 86 billion of these cells.

人腦有大約八百六十億個這種細胞。

They transmit signals down their axons by way of electrical impulses,

它們會透過電脈衝或動作電位

將訊號沿著它們的軸索向下傳輸。

or action potentials.

One neuron can then pass that signal to the next at a synapse

神經元可以用化學神經傳遞質，

從突觸將訊號傳給下一個神經。

by way of chemical neurotransmitters.

The signal is received by the next neuron’s dendrites,

下一個神經元用其樹狀突接收訊號，

propagated down its axon, and passed further along.

傳到它的軸索，再繼續傳下去。

So, the key factors that determine how quickly you think

所以，決定你思考速度 有多快的關鍵因子

include how long it takes to generate an initial action potential;

包括花多少時間產生初始動作電位；

propagate it down the length of the axon; and transport it through the synapse.

沿著軸索的長度向下傳輸； 再透過突觸傳送出去。

We must also factor in the number of neurons involved

我們也要考量使用到多少個神經元

and the distance the signal has to travel.

以及訊號必須要傳輸多長的距離。

Let’s see what this looks like in a simple pathway— your knee-jerk reflex.

咱們用一個簡單的路徑 來說明——膝反射。

A strike to your patellar tendon triggers an electrical impulse

擊打膝蓋骨肌腱就會觸發電脈衝，

that travels up a sensory neuron to your spine.

電脈衝向上跑到脊椎的感覺神經元。

There the signal branches, and for the sake of simplicity,

訊號在那裡分岔，為了簡單說明，

we’ll consider the segment that jumps into a motor neuron

我們來談跳到運動神經元 回到腿部的那個部分。

to journey back down your leg.

The total length of the neurons in that pathway

那條路徑的神經元總長度

is about 1 meter in someone who is 5 foot 5 inches,

對 165 公分高的人大約是一公尺，

and on average it takes 15 to 30 milliseconds from strike to kick.

從擊打膝蓋到反射踢腳， 平均要十五到三十毫秒。

Speed is distance divided by time,

速度等於距離除以時間，

so this signal travels somewhere between 120 to 240 kilometers per hour.

所以這個訊號的行進速度約在

每小時一百二十到一百四十公里。

The initial action potential accounts for 1 to 5 milliseconds

初始動作電位要花一到五毫秒，

and synaptic transmissions only take .1 to .5 milliseconds,

突觸傳輸只要大約 零點一到零點五毫秒，

so the bulk of that time is spent within the axons.

所以大部分的時間是花在軸索當中。

This is consistent with research findings

這和研究的發現一致：

that the average individual neuron sends signals at around 180 kilometers per hour.

平圴每個神經元發送訊號的速度

是每小時一百八十公里。

But speeds can be boosted with myelination and increased axon diameter.

但髓鞘和增加軸索直徑 都可以讓速度增加。

Myelin is a fatty sheath that insulates an axon,

髓鞘是一種脂肪鞘，能將軸索隔離，

preventing electrical currents from leaking out.

預防電流外漏。

Meanwhile, axons with larger diameters offer less internal resistance.

此外，直徑大的軸索 比較沒有內部磨擦力。

These compounded factors can raise the speed of an action potential

這些複合因子能將動作電位的速度

as high as 432 kilometers per hour.

提升至每小時四百三十二公里。

There’s plenty of variation: some people think faster than others,

變化很多：有些人思考速度比別人快，

and your own speed of thought changes throughout your lifetime.

你的思想速度在一生中 也會不斷改變。

In particular, as you reach old age,

特別是當你進入老年時，

the myelin sheath covering your axons wears down,

覆蓋軸索的髓鞘會磨損，

and other neuronal structures degrade.

其他的神經結構會退化。

Back to the dastardly experiment.

回到邪惡的實驗。

Arrows shot from recurve bows fly, on average,

平均而言，彎弓射出的箭

飛行速度約為每小時兩百四時公里。

around 240 kilometers per hour.

Which means that given a sufficiently long, myelinated or large-diameter neuron,

那就表示，若有夠長、 有髓鞘，或直徑夠大的神經，

your thoughts actually could win the race.

你的思想可以贏得比賽。

But… there’s a wrinkle.

但……有個難題。

The arrow and thought don’t leave the gate at the same time;

箭和思想並非同時離開出發點；

first the arrow fires, then once you perceive it,

箭先被射出去， 接著在你感知到之後，

your signal can start down its path.

你的訊號才會開始上路。

Processing images or music, participating in inner speech,

處理影像或音樂、參與內在語言，

and recalling memories all require complicated neural pathways

以及回憶，都需要複雜的神經路徑，

that are nowhere close to the linearity of the knee-jerk reflex.

和膝反射的線性路徑非常不同。

The speed at which these thoughts occur is mostly consistent,

產生這些思想的速度 大部分是一致的，

with variations based on myelination and axon diameter.

會因為髓鞘和軸索直徑而有些不同。

But the duration of a thought will vary significantly depending on its routes,

但思想的時間長度 會因為路線、中途停留，

以及目的地而有很大的差異。

pitstops, and destination.

In this case, when you perceive a threatening stimulus,

在這個例子中， 當你感知到有威脅性的刺激，

you’ll invoke a fear startle response.

你會產生恐懼驚嚇反應。

Similar to the knee-jerk response,

和膝反射反應很相似，

a startle can be involuntary and quite fast.

驚嚇是非自主性的且相當快速。

If the string twangs loud enough,

如果撥弦聲夠大聲，

you might react in less than 65 milliseconds.

你有可能在六十五毫秒之內反應。

More likely though, your startle reaction will be based on sight.

不過你的驚嚇反應比較 有可能是因為視覺而產生。

Our eyes can process an image as quickly as 13 milliseconds,

我們的眼睛處理影像的速度 快到只要十三毫秒，

but computation of what you’re seeing and determining the danger it poses

但計算你看到了什麼 以及判斷它有多少危險性

can take as long as 180 to 200 milliseconds.

可能會要花一百八十到兩百毫秒。

In that time the arrow will have gained a head start of about 13 meters.

在這段時間，箭可能 就已經領先了約十三公尺。

The target is far enough away

如果目標的距離夠遠，

that you’ve got just enough of a chance to catch up,

你還有機會可以追上，

if you can quickly, and quite literally, think your way out.

只要你能快速、且真的 「想出」脫身方式。