Your mortal enemy has captured you and hooked you up to a bizarre experiment. He’s extended your nervous system with one very long neuron to a target about 70 meters away. At some point, he’s going to fire an arrow.
你的死敵抓住了你，並且把你連到了一個怪異的實驗裝置上。他用一條非常長的神經元 把你的神經系統延伸到了一個約70米以外的靶子上。在某一時刻，他將射出一支箭。
If you can then think a thought to the target before the arrow hits it, he』ll let you go. So who wins that race? In order to answer, we have to examine the hardware of thought: neurons. The human brain has about 86 billion of these cells. They transmit signals down their axons by way of electrical impulses, or action potentials.
如果你的思維可以在箭之前擊中靶子，他就會放了你。那麼，誰會在比賽中獲勝呢？為了回答這個問題，我們必須研究一下思維的硬體：神經元。人類大腦中大約有860億個這樣的細胞。它們通過電子脈衝或動作電位把信號向下傳遞給神經軸突。
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.
此後，一個神經元可以把信號傳遞到下一個神經元的神經突觸。傳遞通過化學神經遞質實現。信號被下一個神經元的神經樹突接收，下傳到它的神經軸突，然後接著傳遞下去。
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，決定你思考速度的關鍵因素包括最初產生動作電位，以及將它一路下傳到軸突，再通過突觸來進行傳輸的時間。我們還必須把神經元的數量和信號傳輸的距離等因素考慮進去。
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.
一起來看一看這一過程在膝跳反射這一簡單途徑中是怎樣的。敲擊你的髕骨肌腱會觸發電子脈衝。該脈衝將沿著感覺神經元上傳到你的脊椎。在那裡，信號分散開來。為了簡單起見，我們將考慮跳入運動神經元，又下行回到腿部的那部分信號。
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.
這條途徑中的神經元的總長，就身高為5英尺5英寸的人而言，大約是 1 米。從敲擊到膝跳，平均需要15至30毫秒。速度是距離除以時間，所以這一信號的傳遞速度是每小時120到240公裡。
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.
產生最初的運動電位佔用了1到5毫秒，突觸傳播僅需1至5毫秒，所以大塊時間用在了神經軸突上。該數據與研究發現相一致，即平均每個單一神經元發送信號的速度在每小時180公裡左右。
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軸突直徑而得到提升。髓鞘質是一種脂肪鞘，它把軸突隔絕起來，以防止電波洩漏。同時，直徑較長的軸突擁有較小的內部阻力。這些複合因素可以將動作電位提速至每小時432公裡。
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.
這裡有很多差異：有些人的思維速度比其他人快，你的思維速度也會在一生中發生變化。特別是，當你年紀大了以後，包裹軸突的髓鞘質會發生磨損，其它的神經元結構也會衰退。回到那個歹毒的實驗。由反曲弓射出的箭平均飛行速度大約是每小時240公裡。
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.
這就意味著，只要神經元足夠長，且被髓鞘化或有較長直徑的話，你的思維實際上可以贏得比賽。但是，這裡有一個小問題。箭與思維並不同時出發；首先箭被發射出去，之後，一旦你看到了它，信號就可以開始沿著它的途徑傳遞。
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.
處理圖像或音樂，參與內心獨白，進行回憶都需要複雜的神經通路，它與線性的膝跳反射截然不同。這些思維的產生速度大體上是一致的，其間的區別主要基於髓鞘化和軸突直徑。
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，思維的持續時間卻會出現很大變化，取決於它的路徑，中途站點，和目的地。在這個例子裡，當你察覺到具有威脅性的刺激時，你會觸發恐懼驚嚇反應。類似於膝跳反射，驚嚇可以是非自主的，而且發生得非常快。如果弦聲足夠大的話，你可能會在不到65毫秒內做出反應。
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，你的驚嚇反應將基於你的視覺。我們的眼睛處理一幅圖像的速度可以快至13毫秒，但是，估算你所看到的東西，並決定它的危險性則會需要長達180至200毫秒的時間。到那時，箭就已經領先了大約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.
靶子足夠遠，你正好有足夠的機會趕上，如果你能切實地快速「想」出你的出路來。