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

Translator: Joseph Geni Reviewer: Joanna Pietrulewicz

譯者: Joey Chung 審譯者: Helen Chang

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

葛列格·蓋奇 (GG)：如果讓 你想像兇猛的捕食動物，

you'd probably think of a lion,

你可能會想到獅子，

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

但即使獅子捕食技巧出色，

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

牠捕食的成功率也只有兩成。

Now, one of the most successful hunters

要說動物王國中最成功的捕食者，

in the entire animal kingdom is surprising:

答案可能會讓你大吃一驚，

the dragonfly.

是蜻蜓。

Now, dragonflies are killer flies,

蜻蜓是飛行獵手，

and when they see a smaller fly,

當牠們看到比自身體型小的飛蟲，

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

有 97% 的概率能捕捉到作為食物。

And this is in mid-flight.

而整個過程可以在飛行中完成。

But how can such a small insect be so precise?

一隻如此小的昆蟲 為何有如此高的精準度？

In this episode, we're going to see

在這一集中，我們將會看到

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

蜻蜓的大腦如何讓牠成為致命殺手。

[DIY Neuroscience]

[DIY 神經科學]

So what makes the dragonfly one of the most successful predators

蜻蜓是如何成為動物中

最成功的捕食者之一呢？

in the animal kingdom?

One, it's the eyes.

第一，是牠的眼睛構造。

It has near 360-degree vision.

蜻蜓擁有接近 360° 的視角。

Two, the wings.

第二，翅膀結構。

With individual control of its wings,

通過對翅膀的獨立控制，

the dragonfly can move precisely in any direction.

蜻蜓可以在任何方向精確移動。

But the real secret to the dragonfly's success

但蜻蜓成功的真正秘訣

is how its brain coordinates this complex information

是其大腦可以整合來自眼睛

between the eyes and the wings

和翅膀的複雜信號

and turns hunting into a simple reflex.

並將捕獵行為轉變為簡單反射。

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

為了研究當中的原理， 傑米花了很多時間

socializing with dragonflies.

和蜻蜓相處。

What do you need to do your experiments?

你做實驗需要些什麼？

Jaimie Spahr: First of all, you need dragonflies.

傑米·斯帕爾：首先，你需要蜻蜓。

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

奧利弗： 我用捕蟲網去捉牠們。

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

傑米：越研究牠們，就越害怕牠們。

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

牠們實際上非常嚇人， 特別是在顯微鏡下。

They have really sharp mandibles, are generally pretty aggressive,

牠們的下頜骨非常鋒利， 而且很有攻擊性，

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

我相信這幫助牠們成為捕食好手。

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

GG：為了進一步研究 當蜻蜓看到獵物時的大腦活動，

when it sees a prey,

我們決定偷聽蜻蜓

we're going to eavesdrop in on a conversation

眼睛和翅膀間的對話，

between the eyes and the wings,

為此，我們需要用冰塊麻醉蜻蜓，

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.

並確保翅膀完好無損， 以便我們之後放走牠。

蜻蜓大腦中有很多 特殊的細胞，即是神經元

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

and these neurons are what allow the dragonfly

而就是這些神經元讓蜻蜓

能夠快速見到物件和移動。

to see and move so quickly.

The individual neurons form circuits by connecting to each other

獨立的神經元通過細長的軸突

via long, tiny threads called axons

連接彼此，

and the neurons communicate over these axons using electricity.

進而組成神經迴路， 在軸突上用電信號進行交流。

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

在蜻蜓體內，我們將沿著軸突

放置一些小的金屬線和電極，

along the axon tracks,

and this is what's really cool.

這整個過程很酷。

In the dragonfly, there's only 16 neurons;

在蜻蜓體內只有 16 個神經元：

that's eight per eye

每隻眼睛有 8 個，

that tell the wings exactly where the target is.

用來告訴翅膀目標的具體方位。

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

放置電極後，我們就可以記錄

眼睛和翅膀之間的神經元電信號。

that connect the eyes to the wings.

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

每當有訊息從眼睛傳遞到翅膀，

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

我們的電極都會將這次對話 以電流的形式記錄下來，

and it amplifies it.

並放大電流。

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

我們能看到並聽到電流脈衝，

which we also call an action potential.

我們稱之為動作電位。

Now let's listen in.

現在一起來聽聽。

Right now, we have the dragonfly flipped upside down,

我們馬上把蜻蜓倒置，

so he's looking down towards the ground.

牠現在眼朝地面。

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

我們現在放置一個獵物，或者說目標，

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

這裡我們使用一隻假蒼蠅作為目標。

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

我們將在蜻蜓的視野範圍內移動牠。

(Buzzing)

（電流聲）

Oh!

哦！

Oh, look at that.

哦，你看這裡。

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

快看這裡，但只在 朝特定方向時發生電位變化。

Oh, yes!

哦，好！

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

當我向前移動時，不會出現任何脈衝，

but they're all when I come back.

但回來的時候脈衝會出現。

In our experiments,

在實驗中，

we were able to see that the neurons of the dragonfly

我們見到當目標僅朝一個方向移動時， 蜻蜓的神經元會被啟動，

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

但在向另一個方向移動時卻沒有。

Now, why is that?

這是為什麼呢？

Remember when I said that the dragonfly

記得我之前提及到

蜻蜓擁有 360° 的可視範圍。

had near 360-degree vision.

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

同時，蜻蜓眼睛上有一個 稱為中央凹的區域

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

而這也是蜻蜓視力最敏銳的部分，

and you can think of it as its crosshairs.

你可以把它看作瞄準線。

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

還記得我給你說過蜻蜓能獨立 控制每個翅膀嗎 ?

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

當蜻蜓發現獵物時 會試圖將瞄準線對準獵物，

and along its axons it sends messages only to the neurons

會沿著軸突發送訊號給 控制翅膀的神經元

來對準目標。

that control the parts of the wings

that are needed to keep that dragonfly on target.

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

所以，如果獵物在蜻蜓的左側，

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

那麼只有控制左側翅膀的 神經元會被啟動。

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

如果獵物飛向蜻蜓的右側，

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

那就不需要這些神經元了， 它們就會在靜止狀態。

And the dragonfly speeds toward the prey

當神經元確定好翅膀的角度後，

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

蜻蜓會依照瞄準線朝獵物飛去。

and then boom, dinner.

一擊直中，晚餐到手。

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

現在，這些都是一瞬間發生的事， 這對蜻蜓來說不費吹灰之力，

It's almost like a reflex.

就像本能反應。

And this whole incredibly efficient process is called fixation.

而這個驚人高效的捕獵過程

被稱為固定（fixation）。

But there's one more story to this process.

但是還有一件需要考慮的事情。

We saw how the neurons respond to movements,

我們看到神經元如何回應運動，

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

但是蜻蜓如何判斷誰是獵物呢？

This is where size matters.

這就需要考慮獵物的體型了。

Let's show the dragonfly a series of dots.

讓我們來給蜻蜓展示一系列圓點。

Oh, yeah!

哦，對了！

JS: Yeah, it prefers that one.

傑米：對，牠對那個比較有反應。

GG: Out of all the sizes,

GG： 在所有的體型中，

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

我們發現蜻蜓更傾向於 選擇體型小的目標。

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

換句話說，蜻蜓被設定為 捕捉體型比自己小的飛蟲，

versus something much larger, like a bird.

而不是更大的目標，比如鳥類。

And as soon as it recognizes something as prey,

而只要牠識別出了獵物，

that poor little fly only has seconds to live.

那隻可憐的小飛蟲 只有幾秒鐘的逃生時間。

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

今天我們看到了蜻蜓的腦如何工作

to make it a very efficient killer.

使得蜻蜓成為一個高效的獵手。

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

而且我們要慶幸 自己不是生活在 3 億年前，

when dragonflies were the size of cats.

那時的蜻蜓跟貓一樣大。