How a dragonfly's brain is designed to kill
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0:00 - 0:03Greg Gage: If I asked you
to think of a ferocious killer animal, -
0:03 - 0:05you'd probably think of a lion,
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0:05 - 0:08and for all the wonderful
predatory skills that a lion has, -
0:08 - 0:11it still only has about a 20 percent
success rate at catching a meal. -
0:11 - 0:13Now, one of the most successful hunters
-
0:13 - 0:15in the entire animal kingdom
is surprising: -
0:15 - 0:17the dragonfly.
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0:17 - 0:19Now, dragonflies are killer flies,
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0:19 - 0:20and when they see a smaller fly,
-
0:20 - 0:23they have about a 97 percent
chance of catching it for a meal. -
0:23 - 0:24And this is in mid-flight.
-
0:24 - 0:28But how can such
a small insect be so precise? -
0:28 - 0:29In this episode, we're going to see
-
0:30 - 0:33how the dragonfly's brain is highly
specialized to be a deadly killer. -
0:33 - 0:36[DIY Neuroscience]
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0:36 - 0:39So what makes the dragonfly
one of the most successful predators -
0:40 - 0:41in the animal kingdom?
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0:41 - 0:42One, it's the eyes.
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0:42 - 0:44It has near 360-degree vision.
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0:44 - 0:45Two, the wings.
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0:45 - 0:47With individual control of its wings,
-
0:47 - 0:50the dragonfly can move
precisely in any direction. -
0:50 - 0:52But the real secret
to the dragonfly's success -
0:52 - 0:55is how its brain coordinates
this complex information -
0:55 - 0:57between the eyes and the wings
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0:57 - 0:59and turns hunting into a simple reflex.
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0:59 - 1:02To study this, Jaimie's been
spending a lot of time -
1:02 - 1:03socializing with dragonflies.
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1:03 - 1:05What do you need to do your experiments?
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1:05 - 1:08Jaimie Spahr: First of all,
you need dragonflies. -
1:08 - 1:10Oliver: I have a mesh cage
to catch the dragonflies. -
1:10 - 1:13JS: The more I worked with them,
the more terrified I got of them. -
1:13 - 1:16They're actually very scary,
especially under a microscope. -
1:16 - 1:19They have really sharp mandibles,
are generally pretty aggressive, -
1:19 - 1:22which I guess also helps them
to be really good predators. -
1:22 - 1:25GG: In order to learn what's going on
inside the dragonfly's brain -
1:25 - 1:26when it sees a prey,
-
1:26 - 1:29we're going to eavesdrop in
on a conversation -
1:29 - 1:30between the eyes and the wings,
-
1:30 - 1:33and to do that, we need
to anesthetize the dragonfly on ice -
1:33 - 1:36and make sure we protect its wings
so that we can release it afterwards. -
1:36 - 1:40Now, the dragonfly's brain is made up
of specialized cells called neurons -
1:40 - 1:42and these neurons
are what allow the dragonfly -
1:42 - 1:44to see and move so quickly.
-
1:44 - 1:47The individual neurons form circuits
by connecting to each other -
1:47 - 1:50via long, tiny threads called axons
-
1:50 - 1:53and the neurons communicate
over these axons using electricity. -
1:53 - 1:56In the dragonfly, we're going to place
little metal wires, or electrodes, -
1:56 - 1:58along the axon tracks,
-
1:58 - 1:59and this is what's really cool.
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1:59 - 2:01In the dragonfly, there's only 16 neurons;
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2:01 - 2:02that's eight per eye
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2:03 - 2:05that tell the wings
exactly where the target is. -
2:05 - 2:08We've placed the electrodes
so that we can record from these neurons -
2:08 - 2:10that connect the eyes to the wings.
-
2:10 - 2:13Whenever a message is being passed
from the eye to the wing, -
2:13 - 2:17our electrode intercepts that conversation
in the form of an electrical current, -
2:17 - 2:18and it amplifies it.
-
2:18 - 2:21Now, we can both hear it and see it
in the form of a spike, -
2:21 - 2:23which we also call an action potential.
-
2:23 - 2:24Now let's listen in.
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2:24 - 2:28Right now, we have the dragonfly
flipped upside down, -
2:28 - 2:31so he's looking down towards the ground.
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2:31 - 2:34We're going to take a prey,
or what we sometimes call a target. -
2:34 - 2:36In this case, the target's
going to be a fake fly. -
2:36 - 2:39We're going to move it
into the dragonfly's sights. -
2:41 - 2:42(Buzzing)
-
2:42 - 2:44Oh!
-
2:45 - 2:46Oh, look at that.
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2:50 - 2:52Look at that, but it's only
in one direction. -
2:53 - 2:54Oh, yes!
-
2:55 - 2:57You don't see any spikes
when I go forward, -
2:57 - 2:59but they're all when I come back.
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2:59 - 3:00In our experiments,
-
3:00 - 3:03we were able to see
that the neurons of the dragonfly -
3:03 - 3:06fired when we moved the target
in one direction but not the other. -
3:06 - 3:07Now, why is that?
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3:07 - 3:09Remember when I said that the dragonfly
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3:09 - 3:11had near 360-degree vision.
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3:11 - 3:14Well, there's a section
of the eye called the fovea -
3:14 - 3:17and this is the part
that has the sharpest visual acuity, -
3:17 - 3:19and you can think of it as its crosshairs.
-
3:19 - 3:23Remember when I told you the dragonfly had
individual precise control of its wings? -
3:24 - 3:28When a dragonfly sees its prey,
it trains its crosshairs on it -
3:28 - 3:31and along its axons
it sends messages only to the neurons -
3:31 - 3:33that control the parts of the wings
-
3:33 - 3:35that are needed
to keep that dragonfly on target. -
3:35 - 3:38So if the prey is
on the left of the dragonfly, -
3:38 - 3:42only the neurons that are tugging
the wings to the left are fired. -
3:42 - 3:44And if the prey moves
to the right of the dragonfly, -
3:44 - 3:48those same neurons are not needed,
so they're going to remain quiet. -
3:48 - 3:50And the dragonfly speeds toward the prey
-
3:50 - 3:53at a fixed angle that's communicated
by this crosshairs to the wings, -
3:53 - 3:55and then boom, dinner.
-
3:55 - 3:59Now, all this happens in a split second,
and it's effortless for the dragonfly. -
3:59 - 4:00It's almost like a reflex.
-
4:00 - 4:04And this whole incredibly efficient
process is called fixation. -
4:04 - 4:07But there's one more
story to this process. -
4:07 - 4:09We saw how the neurons
respond to movements, -
4:09 - 4:12but how does the dragonfly know
that something really is prey? -
4:13 - 4:14This is where size matters.
-
4:14 - 4:17Let's show the dragonfly a series of dots.
-
4:29 - 4:30Oh, yeah!
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4:30 - 4:32JS: Yeah, it prefers that one.
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4:32 - 4:34GG: Out of all the sizes,
-
4:34 - 4:37we found that the dragonfly responded
to smaller targets over larger ones. -
4:38 - 4:42In other words, the dragonfly
was programmed to go after smaller flies -
4:42 - 4:44versus something much larger, like a bird.
-
4:44 - 4:47And as soon as it recognizes
something as prey, -
4:47 - 4:50that poor little fly
only has seconds to live. -
4:50 - 4:52Today we got to see
how the dragonfly's brain works -
4:52 - 4:54to make it a very efficient killer.
-
4:54 - 4:58And let's be thankful
that we didn't live 300 million years ago -
4:58 - 5:01when dragonflies were the size of cats.
- Title:
- How a dragonfly's brain is designed to kill
- Speaker:
- DIY Neuroscience
- Description:
-
Dragonflies can catch prey with near perfect accuracy, the best among all predators. But how does something with so few neurons achieve such prowess? Our intrepid neuroscientists explore how a dragonfly unerringly locks onto its preys and captures it within milliseconds using just sensors and a fake fly.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED Series
- Duration:
- 05:17
Brian Greene edited English subtitles for How a dragonfly's brain is designed to kill | ||
Brian Greene edited English subtitles for How a dragonfly's brain is designed to kill | ||
Brian Greene approved English subtitles for How a dragonfly's brain is designed to kill | ||
Brian Greene accepted English subtitles for How a dragonfly's brain is designed to kill | ||
Brian Greene edited English subtitles for How a dragonfly's brain is designed to kill |