DIY Neuroscience
Greg Gage: How a dragonfly's brain is designed to kill
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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.
Greg Gage - Neuroscientist
TED Fellow Greg Gage helps kids investigate the neuroscience in their own backyards. Full bio
TED Fellow Greg Gage helps kids investigate the neuroscience in their own backyards. Full bio
Double-click the English transcript below to play the video.
00:12
Greg Gage: If I asked you
to think of a ferocious killer animal,
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,
predatory skills that a lion has,
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it still only has about a 20 percent
success rate at catching a meal.
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:
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.
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?
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.
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
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.
precisely in any direction.
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01:01
But the real secret
to the dragonfly's success
to the dragonfly's success
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is how its brain coordinates
this complex information
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
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.
you need dragonflies.
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Oliver: I have a mesh cage
to catch the dragonflies.
to catch the dragonflies.
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01:22
JS: The more I worked with them,
the more terrified I got of them.
the more terrified I got of them.
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They're actually very scary,
especially under a microscope.
especially under a microscope.
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They have really sharp mandibles,
are generally pretty aggressive,
are generally pretty aggressive,
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which I guess also helps them
to be really good predators.
to be really good predators.
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GG: In order to learn what's going on
inside the dragonfly's brain
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
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
to anesthetize the dragonfly on ice
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and make sure we protect its wings
so that we can release it afterwards.
so that we can release it afterwards.
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Now, the dragonfly's brain is made up
of specialized cells called neurons
of specialized cells called neurons
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and these neurons
are what allow the dragonfly
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
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.
over these axons using electricity.
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In the dragonfly, we're going to place
little metal wires, or electrodes,
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.
exactly where the target is.
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We've placed the electrodes
so that we can record from these neurons
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,
from the eye to the wing,
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our electrode intercepts that conversation
in the form of an electrical current,
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,
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,
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.
or what we sometimes call a target.
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In this case, the target's
going to be a fake fly.
going to be a fake fly.
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We're going to move it
into the dragonfly's sights.
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.
in one direction.
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Oh, yes!
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You don't see any spikes
when I go forward,
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
that the neurons of the dragonfly
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fired when we moved the target
in one direction but not the other.
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
of the eye called the fovea
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and this is the part
that has the sharpest visual acuity,
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?
individual precise control of its wings?
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When a dragonfly sees its prey,
it trains its crosshairs on it
it trains its crosshairs on it
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and along its axons
it sends messages only to the neurons
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.
to keep that dragonfly on target.
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So if the prey is
on the left of the dragonfly,
on the left of the dragonfly,
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only the neurons that are tugging
the wings to the left are fired.
the wings to the left are fired.
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And if the prey moves
to the right of the dragonfly,
to the right of the dragonfly,
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those same neurons are not needed,
so they're going to remain quiet.
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,
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.
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.
process is called fixation.
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But there's one more
story to this process.
story to this process.
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We saw how the neurons
respond to movements,
respond to movements,
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but how does the dragonfly know
that something really is prey?
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.
to smaller targets over larger ones.
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In other words, the dragonfly
was programmed to go after smaller flies
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,
something as prey,
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that poor little fly
only has seconds to live.
only has seconds to live.
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Today we got to see
how the dragonfly's brain works
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
that we didn't live 300 million years ago
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when dragonflies were the size of cats.
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ABOUT THE SPEAKER
Greg Gage - NeuroscientistTED Fellow Greg Gage helps kids investigate the neuroscience in their own backyards.
Why you should listen
As half of Backyard Brains, neuroscientist and engineer Greg Gage builds the SpikerBox -- a small rig that helps kids understand the electrical impulses that control the nervous system. He's passionate about helping students understand (viscerally) how our brains and our neurons work, because, as he said onstage at TED2012, we still know very little about how the brain works -- and we need to start inspiring kids early to want to know more.
Before becoming a neuroscientist, Gage worked as an electrical engineer making touchscreens. As he told the Huffington Post: "Scientific equipment in general is pretty expensive, but it's silly because before [getting my PhD in neuroscience] I was an electrical engineer, and you could see that you could make it yourself. So we started as a way to have fun, to show off to our colleagues, but we were also going into classrooms around that time and we thought, wouldn't it be cool if you could bring these gadgets with us so the stuff we were doing in advanced Ph.D. programs in neuroscience, you could also do in fifth grade?" His latest pieces of gear: the Roboroach, a cockroach fitted with an electric backpack that makes it turn on command, and BYB SmartScope, a smartphone-powered microscope.
Greg Gage | Speaker | TED.com