How a dragonfly's brain is designed to kill | DIY Neuroscience, a TED series

Translator: Joseph Geni Reviewer: Joanna Pietrulewicz

翻译人员: Ray Jia 校对人员: Harper Chang

Greg Gage: If I asked you to think of a ferocious killer animal,

格雷格·盖奇： 如果让你想象凶猛的捕食动物，

you'd probably think of a lion,

你可能会想到狮子。

and for all the wonderful predatory skills that a lion has,

但即便狮子捕食技巧出色，

it still only has about a 20 percent success rate at catching a meal.

它捕食的成功率也仅有两成。

Now, one of the most successful hunters

要说动物王国中最成功的捕食者，

in the entire animal kingdom is surprising:

答案可能让你大吃一惊，

the dragonfly.

它就是蜻蜓。

Now, dragonflies are killer flies,

蜻蜓是飞行猎手，

and when they see a smaller fly,

当他们看到比自身体型小的飞虫，

they have about a 97 percent chance of catching it for a meal.

他们有 97% 的概率捕捉它，

And this is in mid-flight.

这整个过程仅在飞行时就完成！

But how can such a small insect be so precise?

一个如此小的昆虫 为何有如此高的精准度？

In this episode, we're going to see

在这一集中，我们将会看到

how the dragonfly's brain is highly specialized to be a deadly killer.

蜻蜓的大脑如何造就致命杀手。

[DIY Neuroscience]

[DIY神经科学]

So what makes the dragonfly one of the most successful predators

蜻蜓是如何成为动物中 最成功的捕食者之一呢？

in the animal kingdom?

One, it's the eyes.

第一，眼睛构造。

蜻蜓拥有将近 360° 的视角。

It has near 360-degree vision.

Two, the wings.

第二，翅膀结构。

With individual control of its wings,

通过对每个翅膀的独立控制，

the dragonfly can move precisely in any direction.

蜻蜓可以在任意方向上精确移动。

But the real secret to the dragonfly's success

但蜻蜓成功的真正秘诀，

is how its brain coordinates this complex information

是其大脑会整合来自眼睛 和翅膀的复杂信息，

between the eyes and the wings

and turns hunting into a simple reflex.

并将捕猎行为转变为 躯体的简单反射。

To study this, Jaimie's been spending a lot of time

为了研究清楚其中的原理， 杰米花了很多时间和蜻蜓相处。

socializing with dragonflies.

What do you need to do your experiments?

实验中你都需要些什么？

Jaimie Spahr: First of all, you need dragonflies.

杰米·斯帕尔： 首先，蜻蜓必不可缺。

奥利弗： 我用捕虫网抓它们。

Oliver: I have a mesh cage to catch the dragonflies.

杰米：越研究它们，就越害怕它们。

JS: The more I worked with them, the more terrified I got of them.

它们实际上非常吓人， 特别是在显微镜下。

They're actually very scary, especially under a microscope.

他们的下颌骨非常锋利，很有攻击性，

They have really sharp mandibles, are generally pretty aggressive,

这也帮助他们成为捕食好手。

which I guess also helps them to be really good predators.

格雷格：为了研究蜻蜓 看到猎物时的大脑活动，

GG: In order to learn what's going on inside the dragonfly's brain

when it sees a prey,

我们决定偷听蜻蜓眼睛 和翅膀间的一次对话。

we're going to eavesdrop in on a conversation

between the eyes and the wings,

为此，我们需要用冰水麻醉蜻蜓，

and to do that, we need to anesthetize the dragonfly on ice

and make sure we protect its wings so that we can release it afterwards.

并确保翅膀完好无损， 以便后续进行放生。

蜻蜓大脑中有很多特殊的细胞， 那就是神经元。

Now, the dragonfly's brain is made up of specialized cells called neurons

and these neurons are what allow the dragonfly

这些神经元使得蜻蜓

to see and move so quickly.

能够快速发现和移动。

The individual neurons form circuits by connecting to each other

独立的神经元 通过细长的轴突连接彼此，

进而组成神经回路。

via long, tiny threads called axons

and the neurons communicate over these axons using electricity.

神经元在轴突上用电信号进行交流。

In the dragonfly, we're going to place little metal wires, or electrodes,

在蜻蜓体中，我们将沿着轴突

along the axon tracks,

放置一些小的金属线和电极，

and this is what's really cool.

这整个过程都很酷。

In the dragonfly, there's only 16 neurons;

蜻蜓只有 16 个神经元：

that's eight per eye

每只眼睛各有 8 个，

that tell the wings exactly where the target is.

用来告诉翅膀目标的具体方位。

We've placed the electrodes so that we can record from these neurons

放置电极后，我们就可以记录

眼睛和翅膀之间的神经元电信号。

that connect the eyes to the wings.

Whenever a message is being passed from the eye to the wing,

每当有“消息”从眼睛发往翅膀，

our electrode intercepts that conversation in the form of an electrical current,

我们的电极都会将这次“对话“ 以电流的形式记录下来，

并对电流进行放大。

and it amplifies it.

Now, we can both hear it and see it in the form of a spike,

现在我们能看到并听到电流脉冲，

which we also call an action potential.

我们称之为动作电位。

Now let's listen in.

一起来听听。

Right now, we have the dragonfly flipped upside down,

现在我们把蜻蜓倒置，

so he's looking down towards the ground.

它现在眼朝地面。

We're going to take a prey, or what we sometimes call a target.

我们现在放置一个猎物，或者说目标，

In this case, the target's going to be a fake fly.

这里我们使用一个假苍蝇作为目标。

We're going to move it into the dragonfly's sights.

我们将在蜻蜓的视野里移动它。

（电流声）

(Buzzing)

Oh!

哇哦！

Oh, look at that.

噢，瞧呀。

Look at that, but it's only in one direction.

快看，但只在朝固定方向 移动时有电位变化。

Oh, yes!

太棒了！

You don't see any spikes when I go forward,

当我向前移动的时候 没有出现任何脉冲，

but they're all when I come back.

但回来的时候脉冲出现了。

In our experiments,

实验发现，

we were able to see that the neurons of the dragonfly

当目标仅朝一个方向移动时， 蜻蜓的神经元被激活了，

fired when we moved the target in one direction but not the other.

在另一个方向却没有。

Now, why is that?

这是为什么呢？

之前我说到，

Remember when I said that the dragonfly

蜻蜓拥有 360° 的可视范围，

had near 360-degree vision.

Well, there's a section of the eye called the fovea

蜻蜓眼睛上有一个 称为“中央凹”的区域，

and this is the part that has the sharpest visual acuity,

这是蜻蜓视力最敏锐的部分。

and you can think of it as its crosshairs.

你可以把它看作十字准线。

Remember when I told you the dragonfly had individual precise control of its wings?

还记得吗？蜻蜓能独立控制每个翅膀，

When a dragonfly sees its prey, it trains its crosshairs on it

当它发现猎物时， 会试图将准星对准猎物，

and along its axons it sends messages only to the neurons

它会沿着轴突发送信息

给控制翅膀的神经元，

that control the parts of the wings

that are needed to keep that dragonfly on target.

由这些神经元控制蜻蜓来对准目标。

So if the prey is on the left of the dragonfly,

所以，如果猎物在蜻蜓的左侧，

only the neurons that are tugging the wings to the left are fired.

那么只有控制左侧翅膀的 神经元会被激活。

And if the prey moves to the right of the dragonfly,

如果猎物飞向蜻蜓的右侧，

those same neurons are not needed, so they're going to remain quiet.

那就不需要这些神经元了， 它们会乖乖闭嘴。

And the dragonfly speeds toward the prey

神经元确定好翅膀的角度后，

at a fixed angle that's communicated by this crosshairs to the wings,

蜻蜓就会朝猎物径直飞去。

and then boom, dinner.

当当，晚饭到手了。

Now, all this happens in a split second, and it's effortless for the dragonfly.

所有这些都在一瞬间发生， 这对蜻蜓来说毫不费力，

It's almost like a reflex.

就像是本能反应。

And this whole incredibly efficient process is called fixation.

这个惊人高效的捕猎过程被称为固定。

But there's one more story to this process.

但还有一件事需要考虑。

We saw how the neurons respond to movements,

我们看到神经元如何响应运动，

but how does the dragonfly know that something really is prey?

但是蜻蜓如何判断谁是猎物呢？

This is where size matters.

这就需要考虑猎物的体型了。

Let's show the dragonfly a series of dots.

我们来给蜻蜓展示一系列圆点。

Oh, yeah!

没错！

JS: Yeah, it prefers that one.

杰米：它对那个圆点比较有反应。

GG: Out of all the sizes,

格雷格： 在所有的体型中，

we found that the dragonfly responded to smaller targets over larger ones.

我们发现蜻蜓更倾向于 选择体型小的目标。

In other words, the dragonfly was programmed to go after smaller flies

换句话说，蜻蜓被设定为 捕捉体型比自己小的飞虫，

versus something much larger, like a bird.

而不是更大的目标，比如鸟类。

And as soon as it recognizes something as prey,

一旦它识别出了猎物，

that poor little fly only has seconds to live.

可怜的小飞虫只有几秒钟的逃生时间。

Today we got to see how the dragonfly's brain works

今天我们看到了蜻蜓的大脑如何工作，

to make it a very efficient killer.

使得蜻蜓成为一个高效的猎手。

And let's be thankful that we didn't live 300 million years ago

我们得庆幸自己 不是生活在 3 亿年前，

when dragonflies were the size of cats.

那时的蜻蜓差不多跟猫一样大。