How fast is the speed of thought? - Seena Mathew

翻译人员: C Cheng 校对人员: Yolanda Zhang

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

你的死敌抓住了你，并且把你 连到了一个怪异的实验装置上。

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

他用一条非常长的神经元 把你的神经系统延伸到了

to a target about 70 meters away.

一个约 70 米以外的靶子上。

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

在某一时刻，他将射出一支箭。

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

如果你的思维 可以在箭之前击中靶子，

he’ll let you go.

他就会放了你。

So who wins that race?

那么，谁会在比赛中获胜呢？

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

为了回答这个问题，我们必须 研究一下思维的硬件：神经元。

The human brain has about 86 billion of these cells.

人类大脑中大约有 860 亿个这样的细胞。

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

它们通过电子脉冲或动作电位 把信号向下传递给

or action potentials.

神经轴突。

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

此后，一个神经元可以把信号 传递到下一个神经元的神经突触。

by way of chemical neurotransmitters.

传递通过化学神经递质实现。

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

信号被下一个神经元的 神经树突接收，

propagated down its axon, and passed further along.

下传到它的神经轴突， 然后接着传递下去。

So, the key factors that determine how quickly you think

所以，决定你思考速度的关键因素

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

包括最初产生动作电位，

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

以及将它一路下传到轴突， 再通过突触来进行传输的时间。

We must also factor in the number of neurons involved

我们还必须把神经元的数量和

and the distance the signal has to travel.

信号传输的距离等因素考虑进去。

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

一起来看一看这一过程 在膝跳反射这一简单途径中是怎样的。

A strike to your patellar tendon triggers an electrical impulse

敲击你的髌骨肌腱 会触发电子脉冲。

that travels up a sensory neuron to your spine.

该脉冲将沿着感觉神经元 上传到你的脊椎。

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

在那里，信号分散开来。 为了简单起见，

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

我们将考虑跳入运动神经元，

to journey back down your leg.

又下行回到腿部的那部分信号。

The total length of the neurons in that pathway

这条途径中的神经元的总长，

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

就身高为 5 英尺 5 英寸的人而言， 大约是 1 米。

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

从敲击到膝跳， 平均需要 15 至 30 毫秒。

Speed is distance divided by time,

速度是距离除以时间，

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

所以这一信号的传递速度 是每小时120 到 240 公里。

The initial action potential accounts for 1 to 5 milliseconds

产生最初的运动电位 占用了 1 到 5 毫秒，

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

突触传播仅需 1 至 5 毫秒，

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

所以大块时间用在了神经轴突上。

This is consistent with research findings

该数据与研究发现相一致，

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

即平均每个单一神经元发送信号的 速度在每小时 180 公里左右。

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

但是速度可以因髓鞘化和 增加轴突直径而得到提升。

Myelin is a fatty sheath that insulates an axon,

髓鞘质是一种脂肪鞘， 它把轴突隔绝起来，

preventing electrical currents from leaking out.

以防止电波泄漏。

Meanwhile, axons with larger diameters offer less internal resistance.

同时，直径较长的轴突 拥有较小的内部阻力。

These compounded factors can raise the speed of an action potential

这些复合因素 可以将动作电位提速至

as high as 432 kilometers per hour.

每小时 432 公里。

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

这里有很多差异：有些人的 思维速度比其他人快，

and your own speed of thought changes throughout your lifetime.

你的思维速度也 会在一生中发生变化。

In particular, as you reach old age,

特别是，当你年纪大了以后，

the myelin sheath covering your axons wears down,

包裹轴突的髓鞘质会发生磨损，

and other neuronal structures degrade.

其它的神经元结构也会衰退。

Back to the dastardly experiment.

回到那个歹毒的实验。

Arrows shot from recurve bows fly, on average,

由反曲弓射出的箭平均飞行速度

around 240 kilometers per hour.

大约是每小时 240 公里。

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

这就意味着，只要神经元足够长， 且被髓鞘化或有较长直径的话，

your thoughts actually could win the race.

你的思维实际上可以赢得比赛。

But… there’s a wrinkle.

但是，这里有一个小问题。

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

箭与思维并不同时出发；

first the arrow fires, then once you perceive it,

首先箭被发射出去， 之后，一旦你看到了它，

your signal can start down its path.

信号就可以开始沿着它的途径传递。

Processing images or music, participating in inner speech,

处理图像或音乐，参与内心独白，

and recalling memories all require complicated neural pathways

进行回忆都需要复杂的神经通路，

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

它与线性的膝跳反射截然不同。

The speed at which these thoughts occur is mostly consistent,

这些思维的产生速度 大体上是一致的，

with variations based on myelination and axon diameter.

其间的区别主要基于 髓鞘化和轴突直径。

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

但是，思维的持续时间却会 出现很大变化，取决于它的路径，

pitstops, and destination.

中途站点，和目的地。

In this case, when you perceive a threatening stimulus,

在这个例子里，当你察觉到 具有威胁性的刺激时，

you’ll invoke a fear startle response.

你会触发恐惧惊吓反应。

Similar to the knee-jerk response,

类似于膝跳反射，

a startle can be involuntary and quite fast.

惊吓可以是非自主的， 而且发生得非常快。

If the string twangs loud enough,

如果弦声足够大的话，

you might react in less than 65 milliseconds.

你可能会在不到 65 毫秒内做出反应。

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

但是，更有可能的是，你的 惊吓反应将基于你的视觉。

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

我们的眼睛处理一幅图像的 速度可以快至 13 毫秒，

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

但是，估算你所看到的东西， 并决定它的危险性

can take as long as 180 to 200 milliseconds.

则会需要长达 180 至 200 毫秒的时间。

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

到那时，箭就已经 领先了大约 13 米。

The target is far enough away

靶子足够远，

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

你正好有足够的机会赶上，

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

如果你能切实地 快速“想”出你的出路来。