Reid: This SciShow compilation is supported by LMNT; you can head to drinkLMNT.com/scishow for a free sample pack of electrolyte drinks with any order.

[intro]

[vampiric accent] Happy spooky season from SciShow! [villain laugh, coughs] Ugh, excuse me.

Scary stuff is everywhere, but let's be real; lions, tigers, and bears don't hold a candle to werewolves, zombies and ghosts. The only thing is animals actually exist and monsters don't. And in this Halloween SciShow compilation, we're going to explore the science behind why you might THINK you saw that monster. For example, here's Hank to explain why you might have seen on in the mirror.

[slide: "Why You See Monsters In the Mirror"]

Hank: Mirrors can be pretty freaking creepy. Don't believe it? Go into the bathroom, turn off the lights, and stare at yourself in the mirror. Give it a minute or two, and you'll start to see things. Strange things. That's what puts Bloody Mary up there with Seven Minutes in Heaven and Truth or Dare on the list of best old-school slumber party games. In the '80s movie version, you say Bloody Mary's name three times and summon a terrifying demoness in the mirror, which I'm doing just fine without those particular nightmares, thank you very much. It's weird that looking at your reflection too long makes you see a face in the mirror that's distorted and definitely not yours; that's literally the opposite of what mirrors are for. But even though it's a little freaky, it can tell us a lot about how our brains process images, especially faces.

In 2010, an Italian researcher asked 50 people to look into a mirror for 10 minutes in a dimly lit room and write down everything they saw. Two-thirds of them saw a distorted version of their own face, over a quarter saw someone that they'd never met before, or what looked like an old woman or a child, and I'm literally getting goosebumps - this is freaking me out. Almost half of them -

- almost half of them reported seeing, quote "fantastical and monstrous beings."

Some of this weirdness can be explained by the "Troxler effect," where things in your peripheral vision start to fade as you focus on something in the middle. That's because the neurons in your eyes, like other sensing neurons, stop reacting when they get the same stimulus over and over and over again. It's kind of like how you get used to smells, or stop feeling your shirt on your skin when you're sitting still, or have no idea [touches his glasses] that these glasses are always on your face even though they're always there. But, you don't just see holes; your brain tries to fill in gaps in your visual field by blending with the surrounding scenery. So staring into your reflection's eyes can make your chin, ears, and forehead fade Cheshire-Cat style. 

But the Troxler effect alone doesn't explain why you see other people in the mirror. Psychologists think that that may have to do with the way we perceive faces. Studies like the Thatcher Illusion, where researchers flipped the eyes and mouth of Margaret Thatcher upside down to create a horrifying monster, show that we process the image of a face as a gestalt - a whole that's greater than the sum of its parts. So when certain features that you know are supposed to be part of a face are wrong or disappear, you start to have trouble processing them.

Some researchers think that's what's happening when you stare in the mirror for too long. The Troxler effect causes distortion and fading, which disrupts the assembly of various facial features into a gestalt, therefore making the face feel like it belongs to someone or something else. All 50 participants in the 2010 study reported feeling some amount of disassociation from their reflection. The way they felt about the things they saw in the mirror depended on what they saw; those that saw a terrible monster were understandably more freaked out than those that saw a rando smiling at them. But they all had the sense that the face in the mirror belonged to an "other," a sign that high-level facial processing was being disrupted.

Not recognizing your reflection might not seem like that big of a deal, but there's a good reason it freaks people out. The ability -

- out. The ability to recognize yourself in a mirror is strongly linked to your development of a sense of self. It's something few species can do, and even we humans can't do it until we're about 20 months old. Recognizing your own reflection isn't the only indicator of self-awareness, but it's a pretty important one. Researchers think it's part of a series of milestones that lead to developing your sense of self, as well as the understanding that other people have their own beliefs and desires. So looking in a mirror and seeing a face that's not your own might be more than just creepy; it might actually cause a bit of an identity crisis for a second there.

What psychologists can't explain is why we see monsters. Weird, creepy Bloody Marys? Sure. But these ideas don't fully explain why we see nonhuman faces; it's one of those psychological mysteries that, when solved, could teach us a lot more about how our brains work. So if you're getting chills looking at your reflection, just turn on the lights, maybe don't look quite so long at yourself in the mirror - it's not actually a monster. Pinky swear.

[slide]

Reid: So the monster you saw in the mirror is nothing to worry about. But a hairy one in the forest late at night? There might actually be something there. Except they're probably not monsters. And Michael has a few explanations of what you might really be seeing when you think you encounter a werewolf.

[slide: "Where Did Werewolf Myths Come From?"]

Michael: It's Halloween this week, so we're bringing the science to the supernatural. And this episode is all about our favorite furry frights - werewolves. Werewolf stories date back to at least the ancient Greeks, and they were pretty widespread in Europe; you can find them in Nordic and Celtic mythologies, for example. And we're still fascinated by werewolves. Just ask Team Jacob.

While turning into a wolf is definitely not a thing people do, these myths don't come from nowhere. The idea that a bit could make someone behave strangely or that people could grow thick fur could have come from real scientific phenomena - specifically, a misunderstanding of certain illnesses. The notion that a bite can turn man into beast could have come from rabies, for example.

Rabies is caused by a virus that infects the central nervous system and salivary glands, and like many were-myths, it's transmitted by the bite -

- the bite of an infected creature. People infected by the virus become agitated and behave very strangely; they may hallucinate and suffer from insomnia. Those symptoms arise because the virus harms brain cells and interferes with the chemicals that neurons use to communicate with each other. 

For example, it can mess with the levels of serotonin: a chemical involved in controlling the sleep cycle, feeling pain, and behaviors like aggression. In later stages of infection, the virus invades the salivary glands, sometimes causing excessive salivation. And that saliva contains transmissible viruses, so if the person bites someone else, they can pass along the virus. So, though human-to-human transmission of rabies is rare, our teeth aren't particularly sharp, and we rarely bite hard enough to break skin. Mammals with pointy canine teeth are much more efficient, and rabies is a life-threatening illness. If a patient isn't treated with antivirals and the vaccine before the virus settles in, infections are almost always fatal.

Put yourself in the shoes of a rural farmer in medieval Europe. And oddly-behaving, aggressive dog shows up in your village and bites your neighbor. Then, your neighbor begins acting strangely as well; they're agitated, maybe even aggressive and foaming at the mouth like that scary dog was, and then they die. Back before we understood what a virus was or how they work, a werewolf was as good an explanation as any for how a bite could make a person change like that, especially if you'd heard rumors about people with wolf-like appearances.

Such rumors could have come from real medical conditions like congenital hypertrichosis terminalis, the excessive growth of pigmented hair due to a genetic abnormality. In the past, it was literally called "werewolf syndrome," because people with it grow unusually thick and somewhat fur-like hair on their face and body. The condition is extremely rare, though. Doctors have documented less than 100 cases since the middle ages, and because of that, it's been hard to study. It took almost two decades to suss out what causes the condition in one well-studied family, for example.

In 1984, it was clear they had some kind of mutation on the X chromosome; the location narrowed to a specific region of the X chromosome in 1995, but it wasn't until 2011 that researchers figured out exactly what was happening to the DNA. Turns out, an insertion of DNA in that exact spot alters the expression of a gene called "SOX3," -

- which is involved in hair growth. The gene becomes over-expressed, and expressed in places where it shouldn't be, leading to extra-thick body hair and hair growth on parts of the body that are usually hairless, like a person's eyelids.

Extra hair isn't really harmful on its own, though the condition is frequently associated with other genetic abnormalities that can cause health or development problems. But humans are often unkind to people who look different, so the disorder can have a major psychological toll. People with congenital hypertrichosis used to be called "wolf men" and were often featured at fairs or circus sideshows, which is horrible. But way back before then, their existence could have easily fueled werewolf stories; some of those stories may have even been started by people who actually believed they were werewolves.

People with what psychologists call "lycanthropy" might not look like wolves, but they think they do. They insist their boy has changed, that their canine teeth have gotten longer and pointier, and their body hair has gotten thicker. They may even begin to behave like a wolf, running around on all fours, howling and demanding meals of raw meat. That's because lycanthropy is a kind of "delusional misidentification syndrome," a type of psychological condition where a person... well... misidentifies things. Basically, something's gone awry in the part of their brain that recognizes their physical body, causing them to think they've become a wolf.

If you didn't know much about mental illness - if you were living in medieval Europe, for example - it would be very unnerving if someone began behaving like a wolf and insisting they had grown sharp teeth and long pointy ears. It's not hard to see why you might think they were under the influence of a supernatural entity. But the actual causes of delusional misidentification syndromes remain a bit of a mystery. They're rare and usually associated with schizophrenia, major mood disorders, or injuries due to stroke or trauma, especially ones that occur in the right frontal lobe of the brain. But scientists are only just beginning to understand how our brain constructs what we know as our physical self. In the meantime, doctors can help people with lycanthrophy with antipsychotic medications.

Similarly, there are a lot of options, like cosmetic hair removal, that can help people manage congenital hypertrichosis. So nowadays, we know that conditions like lycanthropy or hypertrichosis, which could have spurred werewolf myths, are nothing to fear. But! You can still be scared of rabies; that is a virus you really don't -

- really don't want to mess with.

[slide]

Reid: The werewolf myths came from science. Rabies virus, extra-hairy genes, and mental illness are all very real things that might lead people to the not-so-real werewolf conclusion. In fact, many Halloween-y concepts can be explained by science, like these three paranormal experiences.

[slide: "3 Paranormal Experiences Explained By Science"]

Hank: From spooky ghosts, to UFOs, to mysterious floating lights, there are all kinds of weird stories out there that seem impossible to explain, unless there's something paranormal going on. But even the creepiest campfire stories can be debunked with the right questions and some careful observation. So here are three times scientists looked into something strange and found a perfectly rational - although, in some cases, still very unsettling - scientific explanation for it. Like, in one supposedly-haunted lab in the UK.

In the late 1990s, people who worked there could often feel waves of fear or shivers, and one engineer saw a terrifying grey apparition from the corner of his eye. But he figured there had to be some reason for it. This engineer also happened to be a fencer, and one day, he brought in his foil - a thin fencing sword - to the lab to adjust it for an upcoming competition. When he set the foil in a clamp, the blade started vibrating, almost like a ghost was shaking it. Except it wasn't a ghost. By moving the foil around the lab and observing it, he figured out that the room contained a low-frequency sound wave, which eventually, he traced back to the lab's new fan.

That explained pretty much all of the spooky stuff that had been going on. The foil shook because the sound wave was at its resonant frequency - a frequency that easily made it start vibrating. All objects have one, it's also why if you run your finger around a glass, it'll sing a nice little song. This wave had a frequency of around 19 Hertz or 19 vibrations per second, which is right below the range of human hearing; it's called "infrasound." And studies have shown that strong infrasound waves can cause uneasiness and dizziness, -

- which can seem a lot like haunting. Because infrasound vibrates through your body's tissues, it can affect your sense of balance, your breathing rate, and your blood pressure. It can even cause apparitions since the resonant frequency of your eyeballs is also about 19 Hertz. So the ghost the engineer saw was caused by his eyeballs vibrating, which is super freaky, actually. And kind of gross to think about. But it was not an actual ghost.

In some stories, something that's said to be paranormal is caught on camera, too. The internet is full of photos of long rod-like insects with multiple sets of wings, and they've been passed off as things like UFOs, aliens, and interdimensional creatures. It turns out that they're... they're bugs. Usually moths. The creation of these ghostly images has to do with how cameras work.

Insects usually beat their wings a lot faster than a camera can capture an image, so something like a moth will flap several times while a camera is recording one frame. And as it's capturing that image, the insect is also moving across its field of view. The result is that the moth looks like a blurry, elongated rod with multiple sets of wings. If you've ever tried to take a long-exposure photograph of anything, you have probably seen something like this. The length of the rod is relative to how fast the insect is moving and how far it is from the camera; the fast and closer it flies, the longer your mysterious, interdimensional visitor.

Cryptozoologists call these "rods" or "skyfish" - I like both of those names a lot. But as cool as they sound, and as cool as it would be to have alien interdimensional skyfish flying around us, these are just mostly moths flying to a different beat. 

Finally, if you've ever been to the tiny city of Marfa, Texas, you might have driven down US Highway 67 and spotted what looked like a UFO in the distance. On some nights, these so-called "Marfa lights" appear above the horizon, hovering and blinking like spaceships; there's even a viewing area for them along the road. But, surprise! They are also -

- not aliens.

Local university students thought they might be caused by car headlights, so in 2004, they did some experiments to... shed some light on the situation. They set up cameras to monitor the lights and a box to measure the traffic on Highway 67. They also tracked a car driving down the road to see if the highway was directly visible from the Marfa lights viewing area.

The results weren't that spooky or surprising; they found that the Marfa lights were probably caused by the atmosphere reflecting headlights from the highway. There was a direct relationship between the number of Marfa lights and the amount of traffic, and the group at the viewing area could even tell which lights corresponded to the car they were tracking. In 2008, these findings were supported by another team who found that the lights could also come from streetlights or campfires.

You'd think it'd be pretty easy to tell whether what your'e looking at is a pair of headlights or an alien spaceship, but the Marfa lights are tricky because they don't really look like headlights. They're often magnified and kind of shimmer. That comes from a mirage, where light rays bend and displace an image; specifically, it's caused by what's known as a "superior mirage," where an image appears above where it should be. It happens when a layer of warmer air sits on top of cooler air, which is the opposite of normal; usually, the lower layers of the atmosphere are warmer because they're heated by the earth's surface. 

Air at different temperatures has different densities, so it bends light at different angles. When light rays pass through temperature inversion, they can bend in a way that creates an image above where the object usually is. And to be clear, when it comes to the Marfa lights, that object is just car headlights on a lonely road, not an alien spaceship.

There are plenty of other stories of the paranormal that are still unexplained, whether because they can't be replicated, or there isn't enough data bout them to come to any conclusions. But sometimes, all you need are the right questions and a healthy dose of skepticism. Also, maybe a fencing foil.

[slide]

Reid: Science teaches us that we can always refresh our understanding of the world and learn new explanations for things we once -

- we once thought were paranormal. 

And this video's sponsor, LMNT, provides a refresh for your electrolytes. It's an electrolyte drink mix designed to replace the sodium lost through sweat during exercise. LMNTs electrolyte drink mix comes in exciting flavors from chocolate to citrus, and they don't even have any sugar. It's vegan-friendly and gluten-free, and if it's not for you, you'll get your money back with a no-questions-asked refund. And because you watch SciShow, you can get a free sample pack of eight single-serving packets with any order. You can take that opportunity to try all eight flavors or share with a friend. To get yours, just head to drinkLMNT.com/scishow or click the link in the description down below. Thanks to LMNT for supporting this SciShow video.

Okay, there's no reason to be afraid of fans, moths, and headlights. But it might make sense to have a healthy fear or some monsters, like zombies. Because, in a way, those are real. And if you don't believe me, just listen to Stefan's explanation of mind-controlling parasites.

[slide: "Mind-Controlling Parasites and How They Affect the Brain"]

Stefan: 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 -

- 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 cow's poop and then eaten by a snail. The larvae develop inside that snail for several months, and 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 the German scientists call 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 mouth parts. And from this strategic spot, it can control the ant's behavior in a bizarrely precise way.

During the day, the infect ant carries on with it's business, "Nothing to see here, just a normal ant doing ant-y 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 brainworm, 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 brainworm 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 -

- 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 as 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. May animals act differently when they'll 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 pupae, laying 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 -

- 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 antenna 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 though 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 -

- 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... Okay, 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 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. 

And unlucky mouse gets 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 to 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 -

- 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.

[slide]

Reid: As it turns out, a lot of these monster myths probably come from your brain and your immune system playing tricks on you. And when it comes to your brain playing tricks on you, maybe the most iconic example is the Ouija board. Here's why they're so convincing.

[slide: "Why Ouija Boards Are So Convincing"]

Hank: If you've ever played with the Ouija board, you're probably familiar with the spooky feeling of another presence moving the planchette. But we can say something with a bit of confidence here; it's not a ghost, it is'your brain playing tricks on you. In fact, psychologists have a pretty good understanding of Ouija boards. They've figure out not only how the planchette moves across the board, but also why we're so easily convinced a spirit is the one behind it.

In a sense, the way we interact with Ouija boards is similar to how we've learned to interact with most of the world - through associations. As infants, we begin learning to associate our behaviors with certain outcomes like, "If I cry, my caregiver will give me food or attention." So after just after a few trials, we can begin to understand how our world works and how to survive in it. But this also means that generally, our brains end up wired to think in terms of cause and effect. It's just that figuring out what caused something can be a challenge, and that's especially true of Ouija boards.

Under normal circumstances, we realize our actions caused some outcome -

- outcome if our behavior is closely linked in time with the effect. In other words, if I reach over and push a planchette, and it immediately moves - cool. My brain will totally know that I did that. But if the outcome happens much later than our action, or if our action wasn't voluntary to begin with, that throws us for a loop, and our brain normally doesn't realize we're responsible. And that is what happens with Ouija boards. 

Overall, the mechanics here are actually pretty simple. The planchette moves thanks to something called the "ideomotor effect." This is when a muscle moves just a little bit without you noticing and without you actually intending it to move, and it's driven by your thoughts and subconscious. So, if you're focusing really hard on the planchette and waiting for it to move, you might not notice that your finger happened to twitch a little toward one of the letters, and your brain won't notice either. So, faced with a spooky, moving planchette, it makes sense that you would just assign causation anywhere you can; you didn't move it, so maybe it was your friend, or maybe it was something spooky.

A key brain region in figuring this out is called the "caudate nucleus," and it deals with motor behaviors and reward-based learning. But the other major player here is the dorsolateral prefrontal cortex or DLPFC. This region has kind of a big job; it figures out who or what caused something to happen. It's just not always great at it. I mean, in its defense, figuring that stuff out is hard. Like, something could have been caused by your actions or by chance or by some other factor.

So this region needs to take in information about tons of only possibly relevant cues and determine which ones are actually important. And while this usually works out, sometimes the DLPFC is just a little overeager to assign credit somewhere. And that means we might superstitiously give credit to something irrelevant just on accident, like a ghost. Admittedly, it could seem like there's a bit of a jump between "your brain doesn't know what caused something to move" to "there is a ghost in the room." But here, a look at personality -

- a look at personality traits may help explain why some people are more inclined to give credit to something supernatural.

Specifically, there's an idea in personality psychology called "locus of control." A person with a strong internal locus of control feels that they are mainly responsible for their outcomes in life, while a person with an external locus of control will give more credit to fate, luck, and chance. And maybe unsurprisingly, where we fall on that spectrum can influence how we interact with Ouija boards.

In a 2018 study of 40 Ouija board players, more skeptical players reported a more internal locus of control. More specifically, this group believed the planchette was being moved by the other player or perhaps even unconsciously by the themselves. Meanwhile, the opposite was true for those who believed the planchette was moved by some outside force; they reported a more external locus of control.

No matter which group you fall into though, Ouija boards can be a lot of fun; they're creating an illusion driven by unconscious movement, an overzealous brain, and personality traits. And also potentially by your friend. But even knowing all of that... they can still be a little spooky.

[slide]

Reid: So we're very capable of convincing ourselves that all sorts of monsters and ghouls are out there. But this Halloween, may the only ones you see be the adorable trick-or-treaters doing their best impersonations.

[outro]