TED | 为啥行动力总是跟不上思想的速度？不一定是“拖延症”的锅

如果你的思维可以在箭之前击中靶子，他就会放了你。那么，谁会在比赛中获胜呢？为了回答这个问题，我们必须研究一下思维的硬件：神经元。人类大脑中大约有860亿个这样的细胞。它们通过电子脉冲或动作电位把信号向下传递给神经轴突。

One neuron can then pass that signal to the next at a synapse by way of chemical neurotransmitters. The signal is received by the next neuron’s dendrites, propagated down its axon, and passed further along.

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。传递通过化学神经递质实现。信号被下一个神经元的神经树突接收，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 include how long it takes to generate an initial action potential; propagate it down the length of the axon; and transport it through the synapse. We must also factor in the number of neurons involved and the distance the signal has to travel.

所以，决定你思考速度的关键因素包括最初产生动作电位，以及将它一路下传到轴突，再通过突触来进行传输的时间。我们还必须把神经元的数量和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. A strike to your patellar tendon triggers an electrical impulse that travels up a sensory neuron to your spine. There the signal branches, and for the sake of simplicity, we’ll consider the segment that jumps into a motor neuron to journey back down your leg.

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。敲击你的髌骨肌腱会触发电子脉冲。该脉冲将沿着感觉神经元上传到你的脊椎。在那里，信号分散开来。为了简单起见，我们将考虑跳入运动神经元，又下行回到腿部的那部分信号。

The total length of the neurons in that pathway is about 1 meter in someone who is 5 foot 5 inches, and on average it takes 15 to 30 milliseconds from strike to kick. Speed is distance divided by time, so this signal travels somewhere between 120 to 240 kilometers per hour.

这条途径中的神经元的总长，就身高为5英尺5英寸的人而言，大约是 1 米。从敲击到膝跳，平均需要15至30毫秒。速度是距离除以时间，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 and synaptic transmissions only take .1 to .5 milliseconds, so the bulk of that time is spent within the axons. This is consistent with research findings that the average individual neuron sends signals at around 180 kilometers per hour.

产生最初的运动电位占用了1到5毫秒，突触传播仅需1至5毫秒，所以大块时间用在了神经轴突上。该数据与研究发现相一致，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. Myelin is a fatty sheath that insulates an axon, preventing electrical currents from leaking out. Meanwhile, axons with larger diameters offer less internal resistance. These compounded factors can raise the speed of an action potential as high as 432 kilometers per hour.

但是速度可以因髓鞘化和增加轴突直径而得到提升。髓鞘质是一种脂肪鞘，它把轴突隔绝起来，以防止电波泄漏。同时，直径较长的轴突拥有较小的内部阻力。这些复合因素可以将动作电位提速至每小时432公里。

There’s plenty of variation: some people think faster than others, and your own speed of thought changes throughout your lifetime. In particular, as you reach old age, the myelin sheath covering your axons wears down, and other neuronal structures degrade. Back to the dastardly experiment. Arrows shot from recurve bows fly, on average, around 240 kilometers per hour.

这里有很多差异：有些人的思维速度比其他人快，你的思维速度也会在一生中发生变化。特别是，当你年纪大了以后，包裹轴突的髓鞘质会发生磨损，其它的神经元结构也会衰退。回到那个歹毒的实验。由反曲弓射出的箭平均飞行速度大约是每小时240公里。

Which means that given a sufficiently long, myelinated or large-diameter neuron, your thoughts actually could win the race. But… there’s a wrinkle. The arrow and thought don’t leave the gate at the same time; first the arrow fires, then once you perceive it, your signal can start down its path.

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，你的思维实际上可以赢得比赛。但是，这里有一个小问题。箭与思维并不同时出发；首先箭被发射出去，之后，一旦你看到了它，信号就可以开始沿着它的途径传递。

Processing images or music, participating in inner speech, and recalling memories all require complicated neural pathways that are nowhere close to the linearity of the knee-jerk reflex. The speed at which these thoughts occur is mostly consistent, with variations based on myelination and axon diameter.

处理图像或音乐，参与内心独白，进行回忆都需要复杂的神经通路，它与线性的膝跳反射截然不同。这些思维的产生速度大体上是一致的，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, pitstops, and destination. In this case, when you perceive a threatening stimulus, you’ll invoke a fear startle response. Similar to the knee-jerk response, a startle can be involuntary and quite fast. If the string twangs loud enough, you might react in less than 65 milliseconds.

但是，思维的持续时间却会出现很大变化，取决于它的路径，中途站点，和目的地。在这个例子里，当你察觉到具有威胁性的刺激时，你会触发恐惧惊吓反应。类似于膝跳反射，惊吓可以是非自主的，而且发生得非常快。如果弦声足够大的话，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. Our eyes can process an image as quickly as 13 milliseconds, but computation of what you’re seeing and determining the danger it poses can take as long as 180 to 200 milliseconds. In that time the arrow will have gained a head start of about 13 meters.

但是，更有可能的是，你的惊吓反应将基于你的视觉。我们的眼睛处理一幅图像的速度可以快至13毫秒，但是，估算你所看到的东西，并决定它的危险性则会需要长达180至200毫秒的时间。到那时，箭就已经领先了大约13米。

The target is far enough away that you’ve got just enough of a chance to catch up, if you can quickly, and quite literally, think your way out.

靶子足够远，你正好有足够的机会赶上，如果你能切实地快速“想”出你的出路来。