[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.20,0:00:03.26,Default,,0000,0000,0000,,Greg Gage: If I asked you\Nto think of a ferocious killer animal,
Dialogue: 0,0:00:03.28,0:00:04.78,Default,,0000,0000,0000,,you'd probably think of a lion,
Dialogue: 0,0:00:04.80,0:00:07.62,Default,,0000,0000,0000,,and for all the wonderful\Npredatory skills that a lion has,
Dialogue: 0,0:00:07.64,0:00:11.34,Default,,0000,0000,0000,,it still only has about a 20 percent\Nsuccess rate at catching a meal.
Dialogue: 0,0:00:11.36,0:00:13.38,Default,,0000,0000,0000,,Now, one of the most successful hunters
Dialogue: 0,0:00:13.40,0:00:15.46,Default,,0000,0000,0000,,in the entire animal kingdom\Nis surprising:
Dialogue: 0,0:00:15.48,0:00:16.74,Default,,0000,0000,0000,,the dragonfly.
Dialogue: 0,0:00:16.76,0:00:18.54,Default,,0000,0000,0000,,Now, dragonflies are killer flies,
Dialogue: 0,0:00:18.56,0:00:20.14,Default,,0000,0000,0000,,and when they see a smaller fly,
Dialogue: 0,0:00:20.16,0:00:23.14,Default,,0000,0000,0000,,they have about a 97 percent\Nchance of catching it for a meal.
Dialogue: 0,0:00:23.16,0:00:24.42,Default,,0000,0000,0000,,And this is in mid-flight.
Dialogue: 0,0:00:24.44,0:00:27.62,Default,,0000,0000,0000,,But how can such\Na small insect be so precise?
Dialogue: 0,0:00:27.64,0:00:29.50,Default,,0000,0000,0000,,In this episode, we're going to see
Dialogue: 0,0:00:29.52,0:00:33.20,Default,,0000,0000,0000,,how the dragonfly's brain is highly\Nspecialized to be a deadly killer.
Dialogue: 0,0:00:33.22,0:00:36.46,Default,,0000,0000,0000,,[DIY Neuroscience]
Dialogue: 0,0:00:36.48,0:00:39.50,Default,,0000,0000,0000,,So what makes the dragonfly\None of the most successful predators
Dialogue: 0,0:00:39.52,0:00:40.74,Default,,0000,0000,0000,,in the animal kingdom?
Dialogue: 0,0:00:40.76,0:00:42.02,Default,,0000,0000,0000,,One, it's the eyes.
Dialogue: 0,0:00:42.04,0:00:43.90,Default,,0000,0000,0000,,It has near 360-degree vision.
Dialogue: 0,0:00:43.92,0:00:45.34,Default,,0000,0000,0000,,Two, the wings.
Dialogue: 0,0:00:45.36,0:00:47.18,Default,,0000,0000,0000,,With individual control of its wings,
Dialogue: 0,0:00:47.20,0:00:49.58,Default,,0000,0000,0000,,the dragonfly can move\Nprecisely in any direction.
Dialogue: 0,0:00:49.60,0:00:51.98,Default,,0000,0000,0000,,But the real secret\Nto the dragonfly's success
Dialogue: 0,0:00:52.00,0:00:55.10,Default,,0000,0000,0000,,is how its brain coordinates\Nthis complex information
Dialogue: 0,0:00:55.12,0:00:56.66,Default,,0000,0000,0000,,between the eyes and the wings
Dialogue: 0,0:00:56.68,0:00:59.26,Default,,0000,0000,0000,,and turns hunting into a simple reflex.
Dialogue: 0,0:00:59.28,0:01:01.66,Default,,0000,0000,0000,,To study this, Jaimie's been\Nspending a lot of time
Dialogue: 0,0:01:01.68,0:01:03.34,Default,,0000,0000,0000,,socializing with dragonflies.
Dialogue: 0,0:01:03.36,0:01:05.30,Default,,0000,0000,0000,,What do you need to do your experiments?
Dialogue: 0,0:01:05.32,0:01:07.66,Default,,0000,0000,0000,,Jaimie Spahr: First of all,\Nyou need dragonflies.
Dialogue: 0,0:01:07.68,0:01:10.14,Default,,0000,0000,0000,,Oliver: I have a mesh cage\Nto catch the dragonflies.
Dialogue: 0,0:01:10.16,0:01:13.30,Default,,0000,0000,0000,,JS: The more I worked with them,\Nthe more terrified I got of them.
Dialogue: 0,0:01:13.32,0:01:16.10,Default,,0000,0000,0000,,They're actually very scary,\Nespecially under a microscope.
Dialogue: 0,0:01:16.12,0:01:19.26,Default,,0000,0000,0000,,They have really sharp mandibles,\Nare generally pretty aggressive,
Dialogue: 0,0:01:19.28,0:01:22.02,Default,,0000,0000,0000,,which I guess also helps them\Nto be really good predators.
Dialogue: 0,0:01:22.04,0:01:25.18,Default,,0000,0000,0000,,GG: In order to learn what's going on\Ninside the dragonfly's brain
Dialogue: 0,0:01:25.20,0:01:26.42,Default,,0000,0000,0000,,when it sees a prey,
Dialogue: 0,0:01:26.44,0:01:28.58,Default,,0000,0000,0000,,we're going to eavesdrop in\Non a conversation
Dialogue: 0,0:01:28.60,0:01:30.14,Default,,0000,0000,0000,,between the eyes and the wings,
Dialogue: 0,0:01:30.16,0:01:32.92,Default,,0000,0000,0000,,and to do that, we need\Nto anesthetize the dragonfly on ice
Dialogue: 0,0:01:32.95,0:01:36.34,Default,,0000,0000,0000,,and make sure we protect its wings\Nso that we can release it afterwards.
Dialogue: 0,0:01:36.36,0:01:40.02,Default,,0000,0000,0000,,Now, the dragonfly's brain is made up\Nof specialized cells called neurons
Dialogue: 0,0:01:40.04,0:01:42.22,Default,,0000,0000,0000,,and these neurons\Nare what allow the dragonfly
Dialogue: 0,0:01:42.24,0:01:43.90,Default,,0000,0000,0000,,to see and move so quickly.
Dialogue: 0,0:01:43.92,0:01:46.98,Default,,0000,0000,0000,,The individual neurons form circuits\Nby connecting to each other
Dialogue: 0,0:01:47.00,0:01:49.62,Default,,0000,0000,0000,,via long, tiny threads called axons
Dialogue: 0,0:01:49.64,0:01:52.90,Default,,0000,0000,0000,,and the neurons communicate\Nover these axons using electricity.
Dialogue: 0,0:01:52.92,0:01:56.38,Default,,0000,0000,0000,,In the dragonfly, we're going to place\Nlittle metal wires, or electrodes,
Dialogue: 0,0:01:56.40,0:01:57.66,Default,,0000,0000,0000,,along the axon tracks,
Dialogue: 0,0:01:57.68,0:01:59.18,Default,,0000,0000,0000,,and this is what's really cool.
Dialogue: 0,0:01:59.20,0:02:01.22,Default,,0000,0000,0000,,In the dragonfly, there's only 16 neurons;
Dialogue: 0,0:02:01.24,0:02:02.50,Default,,0000,0000,0000,,that's eight per eye
Dialogue: 0,0:02:02.52,0:02:04.98,Default,,0000,0000,0000,,that tell the wings\Nexactly where the target is.
Dialogue: 0,0:02:05.00,0:02:08.22,Default,,0000,0000,0000,,We've placed the electrodes\Nso that we can record from these neurons
Dialogue: 0,0:02:08.24,0:02:09.94,Default,,0000,0000,0000,,that connect the eyes to the wings.
Dialogue: 0,0:02:09.96,0:02:12.82,Default,,0000,0000,0000,,Whenever a message is being passed\Nfrom the eye to the wing,
Dialogue: 0,0:02:12.84,0:02:16.58,Default,,0000,0000,0000,,our electrode intercepts that conversation\Nin the form of an electrical current,
Dialogue: 0,0:02:16.60,0:02:17.82,Default,,0000,0000,0000,,and it amplifies it.
Dialogue: 0,0:02:17.84,0:02:20.90,Default,,0000,0000,0000,,Now, we can both hear it and see it\Nin the form of a spike,
Dialogue: 0,0:02:20.92,0:02:23.18,Default,,0000,0000,0000,,which we also call an action potential.
Dialogue: 0,0:02:23.20,0:02:24.46,Default,,0000,0000,0000,,Now let's listen in.
Dialogue: 0,0:02:24.48,0:02:27.94,Default,,0000,0000,0000,,Right now, we have the dragonfly\Nflipped upside down,
Dialogue: 0,0:02:27.96,0:02:30.58,Default,,0000,0000,0000,,so he's looking down towards the ground.
Dialogue: 0,0:02:30.60,0:02:33.58,Default,,0000,0000,0000,,We're going to take a prey,\Nor what we sometimes call a target.
Dialogue: 0,0:02:33.60,0:02:36.10,Default,,0000,0000,0000,,In this case, the target's\Ngoing to be a fake fly.
Dialogue: 0,0:02:36.12,0:02:38.64,Default,,0000,0000,0000,,We're going to move it\Ninto the dragonfly's sights.
Dialogue: 0,0:02:40.64,0:02:42.30,Default,,0000,0000,0000,,(Buzzing)
Dialogue: 0,0:02:42.32,0:02:43.52,Default,,0000,0000,0000,,Oh!
Dialogue: 0,0:02:44.72,0:02:45.92,Default,,0000,0000,0000,,Oh, look at that.
Dialogue: 0,0:02:50.04,0:02:52.24,Default,,0000,0000,0000,,Look at that, but it's only\Nin one direction.
Dialogue: 0,0:02:52.84,0:02:54.08,Default,,0000,0000,0000,,Oh, yes!
Dialogue: 0,0:02:54.64,0:02:56.70,Default,,0000,0000,0000,,You don't see any spikes\Nwhen I go forward,
Dialogue: 0,0:02:56.72,0:02:58.62,Default,,0000,0000,0000,,but they're all when I come back.
Dialogue: 0,0:02:58.64,0:03:00.10,Default,,0000,0000,0000,,In our experiments,
Dialogue: 0,0:03:00.12,0:03:02.62,Default,,0000,0000,0000,,we were able to see\Nthat the neurons of the dragonfly
Dialogue: 0,0:03:02.64,0:03:05.90,Default,,0000,0000,0000,,fired when we moved the target\Nin one direction but not the other.
Dialogue: 0,0:03:05.92,0:03:07.18,Default,,0000,0000,0000,,Now, why is that?
Dialogue: 0,0:03:07.20,0:03:09.06,Default,,0000,0000,0000,,Remember when I said that the dragonfly
Dialogue: 0,0:03:09.08,0:03:11.14,Default,,0000,0000,0000,,had near 360-degree vision.
Dialogue: 0,0:03:11.16,0:03:13.66,Default,,0000,0000,0000,,Well, there's a section\Nof the eye called the fovea
Dialogue: 0,0:03:13.68,0:03:16.58,Default,,0000,0000,0000,,and this is the part\Nthat has the sharpest visual acuity,
Dialogue: 0,0:03:16.60,0:03:19.30,Default,,0000,0000,0000,,and you can think of it as its crosshairs.
Dialogue: 0,0:03:19.32,0:03:23.50,Default,,0000,0000,0000,,Remember when I told you the dragonfly had\Nindividual precise control of its wings?
Dialogue: 0,0:03:23.52,0:03:27.58,Default,,0000,0000,0000,,When a dragonfly sees its prey,\Nit trains its crosshairs on it
Dialogue: 0,0:03:27.60,0:03:30.98,Default,,0000,0000,0000,,and along its axons\Nit sends messages only to the neurons
Dialogue: 0,0:03:31.00,0:03:32.70,Default,,0000,0000,0000,,that control the parts of the wings
Dialogue: 0,0:03:32.72,0:03:35.06,Default,,0000,0000,0000,,that are needed\Nto keep that dragonfly on target.
Dialogue: 0,0:03:35.08,0:03:38.06,Default,,0000,0000,0000,,So if the prey is\Non the left of the dragonfly,
Dialogue: 0,0:03:38.08,0:03:41.86,Default,,0000,0000,0000,,only the neurons that are tugging\Nthe wings to the left are fired.
Dialogue: 0,0:03:41.88,0:03:44.38,Default,,0000,0000,0000,,And if the prey moves\Nto the right of the dragonfly,
Dialogue: 0,0:03:44.40,0:03:47.58,Default,,0000,0000,0000,,those same neurons are not needed,\Nso they're going to remain quiet.
Dialogue: 0,0:03:47.60,0:03:49.54,Default,,0000,0000,0000,,And the dragonfly speeds toward the prey
Dialogue: 0,0:03:49.56,0:03:52.82,Default,,0000,0000,0000,,at a fixed angle that's communicated\Nby this crosshairs to the wings,
Dialogue: 0,0:03:52.84,0:03:54.86,Default,,0000,0000,0000,,and then boom, dinner.
Dialogue: 0,0:03:54.88,0:03:58.58,Default,,0000,0000,0000,,Now, all this happens in a split second,\Nand it's effortless for the dragonfly.
Dialogue: 0,0:03:58.60,0:04:00.18,Default,,0000,0000,0000,,It's almost like a reflex.
Dialogue: 0,0:04:00.20,0:04:04.30,Default,,0000,0000,0000,,And this whole incredibly efficient\Nprocess is called fixation.
Dialogue: 0,0:04:04.32,0:04:06.94,Default,,0000,0000,0000,,But there's one more\Nstory to this process.
Dialogue: 0,0:04:06.96,0:04:09.06,Default,,0000,0000,0000,,We saw how the neurons\Nrespond to movements,
Dialogue: 0,0:04:09.08,0:04:12.00,Default,,0000,0000,0000,,but how does the dragonfly know\Nthat something really is prey?
Dialogue: 0,0:04:12.88,0:04:14.22,Default,,0000,0000,0000,,This is where size matters.
Dialogue: 0,0:04:14.24,0:04:16.76,Default,,0000,0000,0000,,Let's show the dragonfly a series of dots.
Dialogue: 0,0:04:29.00,0:04:30.22,Default,,0000,0000,0000,,Oh, yeah!
Dialogue: 0,0:04:30.24,0:04:32.46,Default,,0000,0000,0000,,JS: Yeah, it prefers that one.
Dialogue: 0,0:04:32.48,0:04:33.74,Default,,0000,0000,0000,,GG: Out of all the sizes,
Dialogue: 0,0:04:33.76,0:04:37.28,Default,,0000,0000,0000,,we found that the dragonfly responded\Nto smaller targets over larger ones.
Dialogue: 0,0:04:37.68,0:04:41.74,Default,,0000,0000,0000,,In other words, the dragonfly\Nwas programmed to go after smaller flies
Dialogue: 0,0:04:41.76,0:04:44.10,Default,,0000,0000,0000,,versus something much larger, like a bird.
Dialogue: 0,0:04:44.12,0:04:46.70,Default,,0000,0000,0000,,And as soon as it recognizes\Nsomething as prey,
Dialogue: 0,0:04:46.72,0:04:49.54,Default,,0000,0000,0000,,that poor little fly\Nonly has seconds to live.
Dialogue: 0,0:04:49.56,0:04:52.14,Default,,0000,0000,0000,,Today we got to see\Nhow the dragonfly's brain works
Dialogue: 0,0:04:52.16,0:04:53.84,Default,,0000,0000,0000,,to make it a very efficient killer.
Dialogue: 0,0:04:54.44,0:04:58.18,Default,,0000,0000,0000,,And let's be thankful\Nthat we didn't live 300 million years ago
Dialogue: 0,0:04:58.20,0:05:01.08,Default,,0000,0000,0000,,when dragonflies were the size of cats.