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Greg Gage: If I asked you
to think of a ferocious killer animal,
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you'd probably think of a lion,
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and for all the wonderful
predatory skills that a lion has,
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it still only has about a 20 percent
success rate at catching a meal.
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Now, one of the most successful hunters
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in the entire animal kingdom
is surprising:
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the dragonfly.
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Now, dragonflies are killer flies,
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and when they see a smaller fly,
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they have about a 97 percent
chance of catching it for a meal.
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And this is in mid-flight.
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But how can such
a small insect be so precise?
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In this episode, we're going to see
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how the dragonfly's brain is highly
specialized to be a deadly killer.
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[DIY Neuroscience]
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So what makes the dragonfly
one of the most successful predators
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in the animal kingdom?
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One, it's the eyes.
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It has near 360-degree vision.
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Two, the wings.
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With individual control of its wings,
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the dragonfly can move
precisely in any direction.
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But the real secret
to the dragonfly's success
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is how its brain coordinates
this complex information
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between the eyes and the wings
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and turns hunting into a simple reflex.
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To study this, Jaimie's been
spending a lot of time
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socializing with dragonflies.
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What do you need to do your experiments?
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Jaimie Spahr: First of all,
you need dragonflies.
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Oliver: I have a mesh cage
to catch the dragonflies.
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JS: The more I worked with them,
the more terrified I got of them.
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They're actually very scary,
especially under a microscope.
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They have really sharp mandibles,
are generally pretty aggressive,
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which I guess also helps them
to be really good predators.
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GG: In order to learn what's going on
inside the dragonfly's brain
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when it sees a prey,
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we're going to eavesdrop in
on a conversation
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between the eyes and the wings,
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and to do that, we need
to anesthetize the dragonfly on ice
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and make sure we protect its wings
so that we can release it afterwards.
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Now, the dragonfly's brain is made up
of specialized cells called neurons
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and these neurons
are what allow the dragonfly
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to see and move so quickly.
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The individual neurons form circuits
by connecting to each other
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via long, tiny threads called axons
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and the neurons communicate
over these axons using electricity.
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In the dragonfly, we're going to place
little metal wires, or electrodes,
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along the axon tracks,
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and this is what's really cool.
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In the dragonfly, there's only 16 neurons;
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that's eight per eye
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that tell the wings
exactly where the target is.
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We've placed the electrodes
so that we can record from these neurons
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that connect the eyes to the wings.
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Whenever a message is being passed
from the eye to the wing,
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our electrode intercepts that conversation
in the form of an electrical current,
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and it amplifies it.
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Now, we can both hear it and see it
in the form of a spike,
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which we also call an action potential.
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Now let's listen in.
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Right now, we have the dragonfly
flipped upside down,
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so he's looking down towards the ground.
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We're going to take a prey,
or what we sometimes call a target.
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In this case, the target's
going to be a fake fly.
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We're going to move it
into the dragonfly's sights.
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(Buzzing)
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Oh!
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Oh, look at that.
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Look at that, but it's only
in one direction.
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Oh, yes!
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You don't see any spikes
when I go forward,
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but they're all when I come back.
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In our experiments,
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we were able to see
that the neurons of the dragonfly
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fired when we moved the target
in one direction but not the other.
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Now, why is that?
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Remember when I said that the dragonfly
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had near 360-degree vision.
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Well, there's a section
of the eye called the fovea
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and this is the part
that has the sharpest visual acuity,
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and you can think of it as its crosshairs.
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Remember when I told you the dragonfly had
individual precise control of its wings?
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When a dragonfly sees its prey,
it trains its crosshairs on it
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and along its axons
it sends messages only to the neurons
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that control the parts of the wings
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that are needed
to keep that dragonfly on target.
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So if the prey is
on the left of the dragonfly,
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only the neurons that are tugging
the wings to the left are fired.
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And if the prey moves
to the right of the dragonfly,
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those same neurons are not needed,
so they're going to remain quiet.
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And the dragonfly speeds toward the prey
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at a fixed angle that's communicated
by this crosshairs to the wings,
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and then boom, dinner.
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Now, all this happens in a split second,
and it's effortless for the dragonfly.
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It's almost like a reflex.
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And this whole incredibly efficient
process is called fixation.
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But there's one more
story to this process.
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We saw how the neurons
respond to movements,
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but how does the dragonfly know
that something really is prey?
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This is where size matters.
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Let's show the dragonfly a series of dots.
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Oh, yeah!
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JS: Yeah, it prefers that one.
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GG: Out of all the sizes,
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we found that the dragonfly responded
to smaller targets over larger ones.
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In other words, the dragonfly
was programmed to go after smaller flies
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versus something much larger, like a bird.
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And as soon as it recognizes
something as prey,
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that poor little fly
only has seconds to live.
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Today we got to see
how the dragonfly's brain works
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to make it a very efficient killer.
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And let's be thankful
that we didn't live 300 million years ago
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when dragonflies were the size of cats.