How Mind-Controlling Parasites Teach Us About Brains


Thanks to Skillshare for supporting this episode
of SciShow. [♪ INTRO] Imagine this: you’re minding your own business
when all of a sudden, you’re mysteriously seized by the overwhelming urge to climb to the roof
of your building after work and just stand there. All night long. Come morning, you head back down and go about
your day as if what you just did was totally normal. And then you do it again and again, every night. You may have heard of parasites that can hijack the brains of their victims and cause them to behave in strange ways like this. But what’s even cooler than what
these parasites can do to their hosts is the question of how they do it. It’s a field of science called neuroparasitology. And by studying these cases of mind control,
scientists can gain deeper insights into how animals control their own brains. One of the most direct ways to take over an animal’s
brain is to move in and make yourself at home. Which is exactly what the Lancet liver fluke
does to the ants it parasitizes. Ants are only one of this flatworm’s three hosts. It needs to move between a grazing animal,
a snail, and an ant to complete its life cycle. And while that might seem complicated, a lot
of parasites have multi-host life cycles like this, which might be because some species
are more abundant and easier to control. By moving through these intermediate hosts, the parasites can make it more likely
they’ll find their way back to their main target, their final host, where the adult
parasites live and reproduce. As their name implies, adult liver flukes
live in the livers of grazing animals like cows. Their eggs are excreted in the cows’ poop,
and then eaten by a snail. The larvae develop inside that snail for several
months, then travel to the snail’s respiratory system, where they’re
covered in slime and excreted. And ants apparently find these slime balls
irresistible. Then the parasite needs this ant to be eaten by
a cow or sheep, which traditionally don’t eat ants. They do eat grass, though, and that’s where
a little mind control comes in handy. After the slime ball is ingested, the flukes
break out of the ant’s stomach. They aim for the ant’s head, but only the
first to get there will make itself comfortable next to one of the ant’s cerebral ganglia,
the ant’s version of a brain. It becomes what German scientists called the
“hirnwurm”: a brain worm. Specifically, it hunkers down at the base
of the ant’s mandibular nerves, the nerves that command the ant’s mouthparts. And from this strategic spot, it can control
the ant’s behavior in a bizarrely precise way. During the day, the infected ant carries on
with its business. Nothing to see here, just a normal ant doing
anty things. But every evening when the temperature drops,
it leaves the colony and spends the night camped out on the tip of a blade of grass. And it doesn’t just sit on the grass. The ant, presumably under the control
of that strategically-placed brain worm, bites down to firmly attach itself,
ensuring it’s not knocked off. Since many grazers feed in the cool morning hours, all the ant has to do is patiently wait to be eaten. Then, if the ant is still alive
when the temperature rises again, it climbs down and carries on
as if nothing is wrong. And this happens every night until a grazer
finally gobbles up the ant. When that happens, the worm that had made
it to the brain doesn’t actually get to enjoy the spoils of all its hard work. But the flukes that were hanging out in the
ant’s body get to make their way to the mammal’s liver to become adults. The brain worm has been too busy piloting
its giant ant suit to develop, so it has to sacrifice itself for its siblings. Scientists are still trying to figure out
exactly how the brain worm compels the ant, but it may employ tactics similar to parasitic fungi
that also get ants to climb up things and bite down. Ophiocordyceps fungi infect ants and other
insects and make them travel to a strategic spot so they can spread their spores. Studies suggest the fungi secrete compounds
that alter gene expression, targeting everything from the ant’s internal clock to its ability
to smell in order to ensure they’ll be in the right place at the right time. And manipulating gene expression is a pretty useful strategy if you want to control movement
behaviors; just ask the hairworm. The parasitic hairworm develops inside crickets,
which live on land, even though as adults, the worms live and reproduce in water. So they get their hosts to drown themselves. The hairworms produce a unique set
of proteins to manipulate their hosts, including ones that look an awful lot like
proteins normally found in insects. These induce changes in
gene expression in the cricket’s brain, altering the levels of several proteins including
ones involved in geotactic behavior, the way something orients itself
in response to gravity. There’s also evidence that the parasite
affects phototactic behavior: the way something orients itself
in response to light. And this ultimately means that the hapless
cricket goes for a swim whether it wants to or not. These studies are helping elucidate the neuroscience of navigation, providing insights as to how animals big and small
sense their world and make their way around. Parasites can also manipulate their
victim’s behavior more indirectly, by making them sick in a useful way. Many animals act differently when they’re
ill, like eating less or being lazy, and these sickness behaviors are
initiated by the immune system. So if you’re a parasite that wants your
host to eat less for some reason, you don’t have to figure out
what neurons or genes to manipulate, all you have to do is trigger the
right immune response. And one wasp has actually partnered with a
virus to turn its host’s immune system against it. The wasp lays its egg in the soft underbelly
of a live ladybug. After about three weeks of developing inside the bug, the wasp larva tunnels out
and encases itself in a cocoon. The ladybug then sticks around to guard this pupa, lying on top of it and twitching
to discourage predators. And that probably happens because the mother
wasp injects a virus along with her egg. The virus replicates inside the ladybug’s
cells, especially brain cells. But while the larva is still inside the bug,
it somehow suppresses the bug’s immune system, so the infected cells are left alone. Then, when the larva leaves to pupate, the
ladybug’s immune system kicks in to fight the virus, and inadvertently ends up helping
it manipulate the bug’s behavior. Scientists think the “bodyguarding” behaviors
are neurological symptoms that occur because of damage the immune system causes to the
bug’s brain when it attacks the virus. They’re still working out the details of
how, but the timing of the different stages of the infection and the onset of different
aspects of the ladybug’s strange behavior line up perfectly. This kind of research can help scientists
gain a better understanding of neurological diseases, especially how behavioral symptoms
relate to immune responses. Weirdly enough, the ladybug is one case where
the victim isn’t doomed. Afflicted ladybugs sometimes recover completely
from their ordeal. Their damaged nerve cells can regrow if they
defeat the virus. For the wasp, that’s totally fine, since
it’s already done what it needed to do. And it didn’t even have to expend energy
to make complicated, mind-altering chemicals. It got the virus to do the heavy lifting. But sometimes, if you want a job done right,
you just gotta do it yourself. The emerald cockroach wasp doesn’t take
any chances. First, a female wasp temporarily paralyzes
a cockroach with a quick venomous stab. Then, she uses her stinger to inject more
venom directly into the cockroach’s brain. She’ll even take her time and poke around
to make sure she’s hitting just the right spot, parts of the roach’s ganglia involved
in locomotor processing. The sting makes the roach calm and complacent. The wasp can then literally lead it by its
antennae to her burrow, where its body is consumed by her young. This zombie-like state is achieved thanks
to a compound in the venom which dials down the excitability of the neurons,
making them less likely to fire. It’s not that the roach can’t fight or
run away, it’s that it no longer wants to. In the lab, affected cockroaches
can still do things like fly in a wind tunnel and
right themselves when flipped over. But even as the larva eats its way
through the cockroach’s organs, it doesn’t make any attempt to escape.
It just waits patiently until it finally dies. Understanding the neurological mechanisms
employed by these wasps can help scientists better understand how brains control decision-making. Research like this can even give us fresh
insights into the nature of free will. Of course, the idea of having
your mind, or even just your body, controlled by another being
is understandably terrifying. But these are all insects with small, simple brains. It’s not like any of this could happen to
us and our big, complex brains, right? RIGHT? Uh… Well… Ok, for the most part, no. Our brains have lots of redundant connections
which act as backup systems, and that means controlling a few neurons
doesn’t have as big of an effect. It would be really hard for a parasite to
control our behavior in a specific way like making us bite down
on something, jump in a pool, or be patient while we’re eaten alive from within. Also, we have these wonderful things called skulls that prevent most parasites from
getting easy access to our brains. So if they wanted to turn on or off specific
regions, they’d have to get all up in there like a liver fluke does to an ant. But to prevent that, we have a handy defense
mechanism called the blood-brain barrier. That’s a layer of tightly packed cells
separating the capillaries that feed the brain from other brain tissue. It keeps junk and wandering parasites that
are circulating in our blood from finding their way to our most vulnerable spots…
well, most of the time, anyways. There is some evidence that one parasite can
manipulate human behavior, although maybe not on purpose. It’s a protozoan called Toxoplasma gondii. It’s able to sneak around that blood brain barrier by infecting the cells that
line the brain’s blood vessels. And that’s exactly what it does in mice. Toxoplasma’s final hosts are cats, but to get there,
they first infect small animals, especially rodents. An unlucky mouse becomes infected when it
accidentally consumes Toxoplasma eggs. The young protozoans find their way into the nerves
and muscles and create cysts inside these cells. And in mice, they seem to make a beeline for the amygdala, a part of the brain involved in processing fear. Though it’s not clear how, these cysts alter
the rodent’s behavior, mostly by making them less afraid of cat smells. As you can imagine, that doesn’t work out
so well for the mouse. But it turns out that if we spend some time
around infected cats that are shedding eggs, the parasites can get inside our brains, too. There, they can live for decades, and some scientists think they mess
with our heads in much the same way. For example, some studies suggest that people infected
with Toxoplasma are more reckless or extroverted, though such results are pretty controversial,
and not all research has backed them up. But such effects, if real, are more like personality
nudges than outright mind control. So, a parasite-induced zombie apocalypse is
probably not something to worry about. But neuroscientists are excited about all
the new things we’re learning from these little puppeteers, especially about human
brains. Understanding mind control at the molecular
level can help neuroscientists better understand how neurons work in general, including ours. And that could lead to a deeper understanding
of how our brains work, or what precisely happens in mental illness. Someday, we might even figure out how to harness
the chemicals these parasites use for medical applications, like to treat mood disorders. And totally not to take control of other people. Probably. But there is one thing that neuroparasitology
is already pretty useful for. And that’s inspiring some pretty creepy
and gruesome horror stories. And Halloween is coming up, so if you’re
working on decorations for your zombie science lab haunted house, you’re going to need a classic horror portrait to tie the room together. All this week, we’re showcasing Skillshare
classes we think you’ll like, and if you’re into art and horror, we think you’ll enjoy the class Paint a
Horror-Themed Portrait taught by Damien Mammoliti. The class is fun and perfect for this time of year,
but really all the lessons are pretty timeless. As a digital artist, Damien shares the steps
of his process to create professional, marketable art. No matter how spooky or not you want your portraits to be, you’ll learn a lot from this class. And Skillshare has over 20,000 other classes
taught by experts in their fields. Just click on the link in the description
to take advantage of the offer from Skillshare to get two months of free access to all of
their classes. And, if you do paint a horror portrait, may
I suggest myself as your inspiration? *Rar!* [♪ OUTRO]

100 thoughts on “How Mind-Controlling Parasites Teach Us About Brains

  1. Anyone else notice a strange change in behavior where their significant other gets particularly amorous or has a need to cuddle just before coming down with a cold? I wouldn't be so sure that we are immune to parasitic mood alterations if not full blown mind control.

  2. Funny how you purposely avoid talking about mind numbing/controlling compounds already developed and used by fun loving groups around the world, like in the Middle East or Mexico!?!

  3. What he doesn't mention is that up to half of all humans are already infected by toxoplasma gondii. In France it's even over 80%.

    I for one welcome our ancient cat overlords.

  4. Staying to the end and listening to the sponsored part seems like mind control to me….I just can't click away until no more talking……

  5. Mind control pharma parasites induce pediatricians to inject aluminum adjuvants into the host (children) which is taken up by an immune system cell ( macrophage) which carries the aluminum to the host's brain and expresses as autism. This neurological disorder is then characterized by the media as a desirable alteration of normal function, which encourages parents to happily participate in the vaccine cult, and the enormously rich and powerful pharma industry prospers.

  6. What about the thing that's happening in young children where the exhibit signs of severe mental illnesses or violence based on having strep or something and then it goes to the brain and there is treatment but most familys can't afford it. Does anyone know what I'm talking about.

  7. I bet there all these crazy viruses and parasites are able to prey on invertebrate brains because they have been around for so long and the viruses and parasites and other creatures have had time to perfect their attacks. I'm sure in half a billion years there will be parasites that target the mammalian brain.

  8. i randomly become such a fearless person and i like cats…… thx toxoplasma gondii now i have a bravery rate of over 9000

  9. Maybe the reason we haven't found any parasites that definitively can control humans is because the parasites are making us think so 😉

  10. And how can these mechanisms involving multiple species supposedly be accidents of evolution? This is not the most simple & reasonable explanation.

  11. Incidentally, every other time I’ve heard of the hairworm that makes crickets drown themselves, it’s been called the Gordian worm; is that another name for it?
    Also, if you’re wondering why toxoplasma can infect humans, I’ve heard that they likely adapted to attack a wide variety of mammals so all kinds of cats, from tabbies to tigers, could get in on spreading toxo, and some of these adaptations accidentally made them compatible with humans.

  12. I wonder if you put had an anode in one ear and cathode in the other, could you make a person's muscles jerk?

  13. I've been terrified of cordyceps since I heard about them years ago. Now I've got a bunch of other stuff to be terrified of. Awesome.

  14. no such thing as more extrx or recx, or not good about less scrarx, or redundant or terrifyinx or storix or not, say, out, ex, can say, out, extx any no matter what, no scared

  15. Those mass murderers that happen on occasion. The ones that seem to have no motive or reason. Wouldn't it be interesting if a parasite was responsible.

  16. It would be great if Science used their studies about parasites to help humans learn how to protect ourselves from them, or get rid of them naturally…
    Really? Use the knowledge about brain worms to make drugs for mood disorders?… jeezus!

  17. Do one for a plant that controls a person's brain. Devil's breath scopolamine. I dont know whether or not to believe in it

  18. S T O P. R a P E I N G. B a b I E S
    Or …..the fact that ,were being g mind controlled// we are mind controlled like by radio waves // ….sweet

  19. Actually, rabies can mind control humans as it causes us, like other mammals, to become aggressive and bite others eventually while also affecting our saliva with itself to spread – real life zombies.

  20. And totally not totally not to take control of other people…..

    Today's video is sponsored by the Umbrella Corporation in conjunction with Google.

  21. While watching this all I could think is in the future these mutating to humankind, and future aliens deeming our world a very strange death world.

  22. Whaaaaat , my teacher didnt tell me anything about the ant.
    She only teach about the cow , the poop , the snail and grass.

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