Daniel and Kelly talk about Toxoplasma gondii, and the "science" of ghost hunting.
Happy Halloween everyone. This is my favorite time of year. The weather's cool, the leaves are changing color here in Virginia, and creepy stuff is in. So this week Daniel and I are geeking out about zombies and ghosts. The zombies I'm going to be talking about aren't like creatures who have been infected by viruses that bring the creatures back from the dead in search of delicious brains. But what are often called zombies in pop science are creatures that are infected by parasites, and then those parasites manipulate their living creatures living hosts into acting in weird ways that benefit the parasite while often hurting the host. But one of the hard things about studying seemingly zombified creatures is that behaviors can change when someone is infected for a lot of reasons. Just because it sounds like a behavior can benefit a parasite, that doesn't necessarily mean that it does. In fact, sometimes we've looked into seemingly zombified creatures and when we look into them more closely, the story that we had been telling ourselves falls apart. Let's think through why this can be so tough, all right, So, imagine you're a kid who's home with a fever. Who does that fever benefit all right, Well, maybe it benefits the sick kid. If the high temperature makes it hard for the bacteria or something to survive and grow, all right, that's option one. Option two, maybe neither benefits. So if the fever gets too high, then maybe that's bad for the kid and it's bad for the bacteria. Anyone who has allergies knows that sometimes immune systems overact and do things that are not beneficial. So there are some instances where something changes about the infected individual that's really not good for the individual or the bacteria. Third option is that maybe the change that happens after infection benefits the parasite. So say a kid comes home with a fever, some parent is definitely going to bend over and give that kiddo a kiss on the forehead to see how warm their forehead is. And if my experience as a parent is any indication that is exactly when the kid is going to sneeze directly into your face and often directly into your mouth. So you could tell a story about a fever being away that parasites are bacterial infections. Transmit from kids to their parents. So we've come up with a fairly plausible story. And I was just spitballing here, but the point is that it's easy to tell a story that sounds kind of plausible. So when you see a story about a creature responding in some way after it gets sick, it's important to consider all the different reasons why that could be happening. So today we're going to start our Halloween show with the chat about toxoplasma GANDHII and how it changes the behavior of the creatures it infects, and we're going to evaluate how good the evidence for these claims actually are. The disconnect between the strength of the claims about toxoplasma gandhi i'm manipulating the behavior of the creature and effects and the actual evidence is kind of spooky. And parents, we talk a bit about the birds and the bees when describing the life cycle of this parasite. Nothing too gratuitous or anything. But now is your chance to pick a different episode for the car ride with your kids if you think that's necessary. All right, Welcome to Daniel and Kelly's Extraordinary and spooky universe.
Hi, I'm Daniel, I'm a particle physicist, and I'm wearing a Halloween costume chosen by my daughter.
I'm Kelly Wiener Smith, and I'm excited because this is the best time a year to not be in California, because the leaves are changed in color and it's gorgeous here in California. Just doesn't have anything on Virginia this time of year. Sorry, Daniel.
Have you been to California in October? The air is wonderfully crisp, it still never rains. It's pretty nice.
I lived there, I've been there in the fall, and it's not as good as Virginia.
All Right, I'm gonna have to come gather some data on Virginia so I can make intelligent comments rather than just take cheap potshots.
Sounds good, although you're coming to visit in March, which is maybe not the best Virginia month.
But oh, I see right.
I'm already hedging my bets.
You're making excuses for it already.
Yeah, that's right, that's right.
Well. I love Halloween also because I usually teach my class in costume, and today I give an exam in my class, and I told them if they came to the exam in full costume. They get extra credit.
What is the best costume your student has ever worn to class?
Somebody came in one of those huge, bl low up dinosaur costumes, took up like three rows of seats and took their exam. It's hard to fill out a scanshow with the little t rex arms, but they did it.
That's commitment. That's actually my daughter's Halloween costume this year. We got her one of those. I can't wait to see how she looks at it. She's gonna have a blast. And I am a giant moth because I like insects, and so I got a moth onesie so that I can still wear it for other things, because I don't want to spend fifty dollars on something I'm gonna wear once. So yeah, it's gonna be a good Halloween in the Wienersmith House.
So you're just gonna hang out in that onesie the rest of the year.
Also, yeah, no, probably I might decide that I really like being a moth and maybe that's all I'm gonna.
Wear Sunday Moth Day at the Wienersmith Farm.
Yeah, just one more way I embarrass my children. The list is getting long.
Well, I give my daughter free rain to choose my costume. I said, whatever costume you pick, I'm gonna wear, which is why I'm now an alien abducting human.
That's fantastic. How hard was it to make that costume?
Oh no, she bought it for sure. Oh and I don't think she listens to the podcast, but she hears me talk about aliens enough to know that the alien theme was going to suit me.
Excellent. It's nice when your kids know you pretty well a little bit. I can't get my husband to wear a costume at all.
What.
No, He's never worn a costume for Halloween as far as I know.
Why is he anti costume?
He's so creative, he's anti fun. I don't know.
Come he writes a webcomic. He can't be anti fun. He makes people laugh. He can't be anti fun.
I don't know what to tell you, man, he's anti fun on Halloween. I guess I tried to get a family costume and he was absolutely no on the family costume thing.
Maybe you should all dress up as him one year, then he's in costume.
I like that, Eric, Thank you. I'm making a note in my Google calendar for next year, everybody dresses up like Zach.
But we are not here today just to so discord in Kelly's family. We are here to talk about Halloween. And because we are science nerds and we'd like to dig deep into science of everything, we're here to talk about the science of Halloween, specifically zombies and ghosts, the biology and physics of Halloween.
I am so excited about this episode, and I'm also exciting because it gives me a chance to talk about probably the most famous parasite that manipulates the behavior of its host, Toxoplasma gandhi. And as someone who got their PhD in this field, I am constantly asked about this parasite, and I am constantly frustrated by the disconnect between what people think we know and what the evidence actually supports. So, just like usual, I am going to throw water on everyone's fun. But there's still some cool things to learn along the way, so it'll be okay.
So you're saying it's not just physics that has like nonsense, popsy clickbait misinformation, it's also biology.
Oh my gosh, it's also biology. I mean, we're lucky because we have Ed Yong who writes about parasites that manipulate host behavior, and he's like, super good about evaluating the evidence, but not everybody is quite that careful. And it seems to have emerged in the public consciousness that Toxoplasma gandhi absolutely makes rodents attract to cats and gets the meetn by it and changes human behavior and all sorts of weird pays.
But let's start with the connection of Halloween. Do you chose this paraside because it kind of makes things into zombies? Is that right? What's the zombie connection between Toxoplasma gandhi and Halloween?
All right, So every field has their like thing that everybody fights about and they get upset about, and the use of the phrase zombie really divides my field. So there are some people who are like, well, if you call it a zombie, people are going to think that the animal that got infected died and then came back from the dead. And I'm like, I just feel like you're not giving the general public enough credit, Like, I don't think anyone thinks that they're being brought back from the dead. What do you think is that fair to say?
Yeah, that's a great question. I think my first thought when I hear, zombie is definitely the walking dead, right, like these folks have been killed and now they're like shuffling around. But I've seen enough zombie movies and science fiction in general to appreciate this like a broadening of the category. And you know, people being infected by some sort of disease which makes them want to eat brains and shuffle around and like are they or not doesn't seem to be really crucial to being a zombie. It's more like, you know, drooling a lot, shuffling along and wanting to eat brains. So it'd be pretty cool if there was a real life biological effect that made people act like the zombies in the movies we see. I think people would accept that as a zombie.
Okay, well that's not what I'm talking about today. No, it's not like that. I still feel like if you use the word zombie, then people think like, okay, some infectious something that's changing the behavior as high decked the behavior, And that's really all we mean today. And so it's a way to try to make the topics sort of accessible and exciting to a general public. But it has its drawbacks because I guess, just like any analogy. It's not perfect and it falls flat in some ways, but I like it anyway.
And just to set the context a little bit more like, I can be infected by some bug or even some parasite, but doesn't change my behavior. I mean, maybe I get sick, but it doesn't make me like change what I eat or decide I'm gonna study biology instead of physics or some crazy mind bending misdecision in life, or live in Virginia or something insane. Right, I'm still who I am mentally. So you're saying that there's a category of bugs or parasites whatever that also change the way your brain works, and so the decisions.
You make, yes, and those decisions that you make are decisions that benefit the parasite and may or may not benefit you. So you know the eating brains in the zombie movies, you know, you take a bite out of somebody and that transmits the parasite in the saliva to another individual. And maybe the eating brains is a side effect. I don't know, but so it's got to benefit the parasite in some way, and often at the expense of the host.
Okay, So now I'm mentally imagining, you know, the rat and ratitude that sits on the guy's head and pulls on his hair and controls him. Basically, you're like being driven by this thing. You're not really making your own decisions and your own best interest anymore. You're being used as a vessel for whatever it is that's infected you, and it's controlling you.
Yes, And it's usually not all or nothing. It's usually like a very specific Sometimes it can be a feature of the way that you look, or a certain set of behaviors that change. It's often when we're talking about actual cases where parasites are manipulating the behavior of the creature they infected, it's actually kind of targeted as opposed to like a wholesale shambling along change in everything that you do. But yes, you're essentially to some extent under the control of another individual.
On that topic, one of my favorite Halloween costumes ever is the rat from Ratitui sitting on somebody's head, and this nerdy engineer actually designed one where the rat is like moving and controls the person like a puppet or really hilarious. That's awesome, But let's not talk about Ratituvi and fictional zombies anymore. Let's talk about the actual science. So in what way does Toxoplasma gandhii fulfill this category of zombie ish kind of takeovers?
All right, Well, first let's just talk about some background on this organism. It is sometimes called the most successful parasite on the planet. It can infect just about any warm blooded animal, so beluga whales have it, hyenas have it, rodents have it, humans have it, birds have it. It infects a lot of stuff.
But what is it? Is it like a little worm? Is it a bug?
It's like a little protozoan parasite, so it's eukaryotic, but it's very small, single cells.
So it's a single cell, has a nucleus. It's basically a tiny little critter.
It is basically a tiny little critter, that's right. And so a really quick jargon distinction which might be helpful is that, you know, usually when people talk about pathogens, they're talking about bacteria and viruses, things that give you like the cold and the flu. When they're talking about parasites, we're usually talking about eu carryouts. So organisms with like a nucleus and a cell wall and stuff, and so Toxoplasma gandhii is a parasite, not a pathogen. Not a pathogen, okay, And so.
It infects a huge number of things worldwide, Like do you have it? Do I have it?
So there's probably like a eleven percent chance that either one of us happens to have it.
What that's very high.
Yeah, in the US, about one in ten people have it. Worldwide, about one in three people have it. And there's a bunch of different ways that you can get it. And this is what makes the parasite so successful and so mind blowing is that those parasites have like one or two paths to their next host. Toxoplasma gandhi is like amazing in its diversity. So let's start with cats. So cats are in any different species of cat is a very important kind of host for Toxoplasma gandhi. This is where the parasites get together and have sex. So it's called the definitive host, and I think of it as that's definitely where they're going to be having sex. And that's how I remember that. You're welcome everyone, and so like we can have a whole episode actually on why evolutionary biologists think sex is beneficial in general, But it's something about mixing genetic material up so that you can have some diversity for dealing with things that might be happening in the environment or for battling the host immune system.
And so these guys can only reproduce inside the guts of cats, or there's something about that environment that's better and they can do it elsewhere also, or is it just really only inside cat guts.
That is only where sexual reproduction happens. So we're going to talk a little bit later about places where they can do asexual reproduction where you can essentially just think they're like copying and pasting the exact same cop be over and over and over again. So this is where they get to like swap genetic material to hope to like stay ahead of the immune system arms race they're going through with the other animals that they're trying to infect.
And what is it about cat guts that's so especially romantic?
Mm? Wow, that's a great question.
I mean, it's not hard to imagine you find yourself inside a catgut with somebody else that's a dot. One thing leads to another.
So this is a kind of parasite that's called trophically transmitted, which means a host that's infected gets eaten by a predator, and that's how the parasite makes it to the next host. And in different systems, like in trematodes and nematodes and tapeworms, like lots of different kinds of parasites have this system, and there's usually one species out of all of them in there where sexual reproduction happens, and then in the other hosts they just kind of replicate asexually. And to be honest, I don't know why they're not able to flexibly reproduce sexually in all of those hosts. Maybe I'll look that up and we'll do a different show on it. I don't know why it's just cats. It seems like it would be to be able to do it everywhere. But the other thing about these cats is after they reproduce sexually, they produce a stage called oocysts, which I'm just going to call eggs for the rest of the conversation because it just makes it easier.
Please do I didn't want to pronounce that word.
Yeah, maybe I'm saying it wrong. Who cares. But they get pooped out into the environment when the cat poops, and that's how the parasite gets back out into the environment to infect a bunch of other organisms.
So don't eat cat poop is the lesson here.
Well, it's not that simple, right, because cat poop looks like cat poop at first, right, that's pretty obvious. But over time, cat poop gets like worked into the soil and you might not know there's cat poop, and these eggs can stay in the environment for a really long time.
This episode is going to make me like cats less, Kelly.
Unfortunately, yes, it will outdoor cats in particular less. So like if you have a garden and a outdoor cat comes by and poops in your garden and you don't realize it, and it gets mixed in with the soil, then maybe one day you'll pull a vegetable not rinse it sufficiently, and then you'll get infected. Or you'll be gardening and you get the eggs on your hands and you don't realize it. They're like microscopic, and then you go to eat something else before washing your hands, and you get infected. And this is also how like birds and rodents and stuff like that get infected. Once you get infected, they get ingested and then they move out into your muscles and into your brain.
What about the blood brain barrier I hear all about. Isn't that my vaunted protection for my brain cell.
Matter doesn't work for this parasite. In fact, the parasite goes into your neurons, and that's what makes it actually impossible to get rid of once you're infected. If you're get infected with this parasite, you're gonna have it.
Forever, forever. There's no way to get rid of it.
No, no, because we can't get medication like into your neurons.
Oh wow, Yeah, this thing is pretty clever and insidious. I'm terrified now.
Most successful parasite on the planet.
This is appropriate for Halloween.
Yes, it's some spooky stuff. So when it first gets in there, it starts copying and pasting itself like crazy, and you feel kind of like you have the flu. Some people feel worse than others, Like I have a friend who found out he got infected by toxoplusmos by bringing in two feral kittens into his house. And when he was changing the litter box, he must not have like washed his hands well enough, or maybe they like you know, scratched around in the litter box and then walked on the kitchen table or something like that. And so he got infected. His lymph nodes swelled up, and he called me and he was like, what's gonna happen to me? Now?
You're a zombie. Forget it. That's why life is over.
So you feel kind of crummy for a while.
Wait, but how are these things reproducing in your brain? Does that mean they're eating your neurons? Like where are they getting raw materials and energy? Like what are they gobbling?
They are gobbling some nutrients. A lot of parasites at this stage are pretty energy efficient, So if they were to straight up kill a host while replicating in their brain, they probably would not have matured to the stage where they can survive transmitting to the next host. So often there's like this stage in between when you first infect a host and when you can survive if that host gets eaten to live in the next host, and so you usually parasites are like pretty careful about energy usage, so they don't like totally kill the host or like cause it to I don't know, fall off a bridge or something. But so, yeah, they're being pretty energy efficient, but they are replicating. You're feeling kind of grummy.
And they're active in your brain. Is this how they're changing your behavior somehow?
We don't know, So it does seem like behavioral changes have something to do with either changes in dopaminergic activity. So dopamine is a neurotransmitter you have in your brain. The parasite has genes for I think it's called tyrosine hydroxylase, and that's the limiting factor in the production of dopamine. So all the other stuff that you need to make dopamine is present on the inside of a neuron, but when you dump tirosine hydroxylase in there, the rest of the reaction just happens and you get dopamine.
Isn't dopamine good? Don't you want dopamine? Dopamine makes you feel good, right.
I mean, dopamine is good. It makes you feel good, but it also controls a bunch of other sorts of behavior. Presumably our brains are making something like the right amount, and then the parasite is notching the us up, so you're making more of it than you would have wanted.
Now I'm imagining happy zombies, all these people walking around mind the grinning. Oh well, they're all infected. Look at them.
Life is better with tuxo.
If you meet somebody who's grumpy, you know they're not infected. See, And that's the what to tell.
Yeah, And there have been some experiments where they've given rodents drugs for people who have sort of dopaminergic imbalances or imbalances of dopamine in their brain, and a lot of the weird behaviors that the rodents do sort of either get tamped down or go away. So it does seem like dopamine has something to do with it. But one of the things we've discovered in this field is that nothing is ever straightforward, and I mean the field of how parasites change the behavior of the creatures that they infect, It almost always involves lots of different things. And so there's also some evidence that it's just like the whole brain has inflammation when the parasites are in there, and it might be that generalized inflammation causes things. The parasites might also be localizing in certain parts of the brain and making behaviors weird. It might also have something to do with argentine vasa pressin or something to do with testosterone, So you might notice that in the outline I hadn't put anything about mechanisms because it's just like such a mess right now. There's a lot of different things it could be.
So it's active in the brain. It probably changes brain chemistry. We don't understand completely the mechanism for how it's doing that. Are there behaviors though in people that we can identify as due to this impact, even if we don't have all these little pieces that connect the dots. Are there characteristic ways that it changes people's behavior? Or is it mostly in cats that we notice the change in behaviors?
So cats don't usually show behavioral changes, So the parasites replicating in the gut, we haven't associated any behavioral changes with that. Humans are interesting. So we're jumping ahead a little and that's okay. But so usually what happens with like a rodent that gets infected is you see some behavioral changes, and then when the cat eats the muscles of that rodent, the parasite gets back to the cat. So usually manipulation is supposed to help with some transmission goal for the parasite. So when you're in a rodent, the goal is to get it eaten by a cat, but with humans, we don't usually get eaten by cats.
Sometimes we do big cats.
Yeah, yeah, sometimes big cats, but like it's pretty rare and so we are kind of a dead end from the perspective of getting back to cats. There are some other ways that we can pass it. For example, men can pass it to women during intercourse. We think when I think about that, I'm like, ah, I'm so glad I'm not dating anymore anyway, sorry everyone. Moms can pass it to their children. It's called trans placental, so it goes from the mom to the baby. So if mom gets infected for the first time ever when she's pregnant, it can pass into the fetus. Or if mom gets infected for the first time when she's breastfeeding, I can do trans mammory transmission, which means it goes across the memory lands during breastfeeding into the baby. It still has some options to get from host to host, but we're probably not back to cats. But it is associated with behavioral changes in humans. In humans, right after that stage where it's replicating like crazy, it kind of slows down. It slows its replication. But there's still some evidence that it changes human behaviors. And the interesting thing about like the study of this is there's this guy named Yaroslav Flager. He's a Czech scientist, and apparently he was like, you know, I do a lot of behaviors that really aren't in my own interest, and I just kind of do a bunch of weird stuff. I wonder if that, like brain infecting parasite is to blame. Always makes me wonder like is he just looking for excuses for like, well, I'm a jerk, but it's not my fault I'm infected by this parasite.
All right, I want to hear a lot more about Yaroslav and his zombie research and how he wrote zombies into his proposals to get big money from science foundations. But first we have to take a quick break. So go clean up your cat litterbox to keep your family safe and come right back. All right, we're back, and we're talking about the science of Halloween, more specifically zombies. What are they in biology? Are they really like zombie behaviors? And is toxoplasma GANDHII All it's been cracked up to be in the popular science literature. And you were telling us about a guy who's been doing research into the impact on humans of this little bug. Tell us what he did and what he learned.
Well, so what he was doing was he would draw blood from a group of people. And when you look at people's blood, if you've been infected by this parasite, which you'll have forever, your immune system mounts a response to it, and you always will have that signature of the immune system response in your blood Forevermore So, if you draw blood, you can look at the blood and say, Okay, this person was definitely infected by the parasite at some point. You don't know when, but you know that at some point they were infected, and the parasite is probably just chilling out in the brain.
Now, okay, Because if you have it, you have it forever, right, So you're infected at some point, you're still infected, that's right. This is just a way to tell who's got it and who doesn't have it.
Yep, right, So by drawing blood, you don't need to like invasively dissect someone's brain to know if they've got it. You can just draw blood, and that way you know who's got it and who doesn't, and then you can give people personality tests, and you can look for correlations between the answers that they give on those personality tests and their infection status. Does that make sense?
It does, But these correlational studies are really hard to interpret, right, Like you might just be selecting for cat people versus dog people, and there's a whole lot of potential confounding variables there, right.
Amen, So we have reached the first of my main problems with this field. It could be that there's some third behavior that predisposes people to getting infected, and then when you give them this personality test which you're really measuring, is that they have this behavior to begin with, and that's what got them infected necessarily that the parasite gave them the behavior.
So what you really need is some good control where you take a person, you clone them, then you infect them, then you create a perfectly identical world for them to experience, and then you see their changes in behavior. Why don't people just do that experiment? Kelly? Biology is so easy, that.
Sounds so ethical, it does, But maybe that's why we have it yet.
See, I just don't have those scientific bones. Because particles don't have consent forms, they don't have rights. We annihilate them all the time. No big deal. They don't have a union.
It's great, no IRB committees. I'm jealous. I mean, there are some ways to get at this, Like if you do cohort studies where you follow individuals from the beginning of their lives and you regularly measure their behavior and you regularly measure their infection status, then maybe you can start to disentangle what parasites changed after infection. And these cohort studies are really expensive, really time consuming. But without doing controlled infections, that's probably the best we can do. But there's not a lot of studies that have done all.
Right, so we've qualified this already by saying we don't know what we can learn from these studies. But tell us what do the studies reveal?
Okay, So here is the stuff that's sort of exciting to talk about over tea or over beer or something. Okay. So people who are infected tend to seek novelty less, so they're less likely to want to go out and try new things. Don't know why. There's a lot of sex specific differences. So women who are infected tend to be less suspicious, and men who are infected tend to be more suspicious.
And are men who are infected less likely to wear Halloween costumes?
Oh, it depends on how novel those costumes are. You know, if they're comfortable with it, maybe they're.
Fine, non novel, non suspicious costumes. That's your pitch to zact next time.
Well, I don't know if he's infected or not. It's hard to say. He does work in the garden a lot.
There you go. See, I'm starting to ask questions.
Here you should. And then women who are infected tend to be more warm and like caring, and men tend to be either less warm or unchanged by the parasite.
Interesting.
I get a lot of questions about like does this parasite turn people into crazy cat ladies? But actually the evidence is that women who are infected tend to think cat urine smells less good. They're like, oh, this is an unpleasant smell.
Cat Urine already smells zero good. How can you be hit less good than zero?
See, there's various levels of repulsion, okay, and infected women are more repulsed, but infected men relative to uninfected men, rate the smell of cat urine as being more pleasant. What so maybe crazy cat men. I don't know. There are some quantifiable effects at the country level. Also, a friend of mine looked at personality aggregate scores by countries and also the percent of people in a country who are infected, and we tend to have like pretty good data on percents because often when women are pregnant, they'll get a test to see if they have the parasite. Because if you have the parasite already, your immune system probably has it in check and it's not going to transmit to your fetus. But if you get infected, well you're pregnant, it can transmit. So if you are pregnant and you're not already infected, then you're often told like, don't change any litter boxes. Have your partner do that. But anyway, so we've got these country level scores and countries with more toxoplasma gandhi I tend to be more neurotic.
Which countries are more neurotic?
Come on, oh all right, let's look up Lafferty's paper real quick.
I want to slander some nations here. I'm gonna guess more Pacific, more tropical, more equatorial, is more laid back. And more northern colder, it's going to be more neurotic. That's going to be my totally uninformed Basian prior on this one.
So this paper was some two thousand and six, so it looks like Yugoslavia, according to this study, had sixty seven percent prevalence, and then Hungary had fifty nine percent. Brazil was it sixty seven percent. So those are some of the top countries. That doesn't necessarily mean that the most neurotic. It's like an association, there's some move along that correlation line, but those are some of the more neurotic countries, some of the countries with the higher prevalence of the parasite countries with the lowest prevalence. I'm seeing Finland is at like sixteen percent, so is Israel. Norway is at nine percent. South Korea is only at four percent.
That's basically the opposite of what I predicted. I predicted like Norway and Finland would be very neurotic and Brazil would be very chill.
So why would nor would be very neurotic? They were pretty laid back when I was there. They take weekends off in Norway, they were serious about that. They take August off Man.
Yeah, they are like the richest nation on earth because of their oil wealth, so maybe that helps. Maybe their toxoplasma GANDHII infected them and told them where the oil was going to be. Oh wait, no, you're saying they're less infected, they're more infected. I'm confused.
They're less infected, so probably statistically they would be expected to be less neurotic.
All right, So most of the zombies on Earth you're saying are in Brazil, Hungary and the former Yugoslavia.
Yes, that's probably the right conclusion.
And maybe apology to all of our listeners in those countries.
That's right. So there's also a bunch of other correlations. We probably don't want to spend too long on this because I'd also like to get to the rodents real quick and still leave you some time to talk about ghosts. But there are some worrying things. There's like association with suicides, association with schizophrenia, association with being more likely to be in a traffic accident, which we think is maybe because of a bit of a delay in reaction times. So it's not like they're driving from one side of the road to another like crazy people. Acting like they're drunk. It's just that if they're in a moment where they need to make a split decision, they're a little slower to respond. And we don't know for sure that that's what it is, but that's one of the working hypotheses right now.
All right, So we see these correlations between infection and behavior. We don't know the calls of mechanism. We don't really understand how it works from like a micro biochemical point of view. Do we understand things better in other creatures where we can actually do experiments like cats and rodents that life cycle, like, does it change the behavior of cats and rodents in some way that benefits the parasite?
Well, for both humans and rodents, there are studies that don't always say the same thing. So you collect to the same data in two different studies and sometimes you find an effect and sometimes you don't. That's complicating.
Science is hard.
Science is so hard. But at least with rodents you can do the controlled infections that you can't do in humans, so you can look at how behavior changes following infection. And one of the most exciting things about rodents studies is this thing that's become called fatal feline attraction.
I want to see that movie. That sounds great.
It is, Yeah, it's such an interesting idea. So the idea is that rodents, when they're not infected, they smell cat urine, they freak out. They avoid the area because that's the smell of a predator. They don't want to get eaten. So if they can smell that a cat has been around, they don't want to be in that area. Makes sense, whereas rodents that are infected tend to spend more time in those areas, almost as though they're attracted to those areas. And there were some studies done that show that, like you know, when you have an uninfected rodent, the part their brain associated with fear kind of lights up when they smell cat urine, But when you have infected animals, the part of their brain associated with getting excited about a potential partner lights up. So it's almost like the parasite is changing this response to this chemical cue from absolutely petrifying to like something that's maybe kind of sexy. But two problems here. One, you don't always see this effect. Sometimes you do the controlled infections and you don't see this attraction to the smell of cat urine, and it looks like maybe it differs depending on like, are you using an inbred rodent strain that's been living in the lab for a really long time. Are you looking at males or females? How long has the rodent been infected? What strain of Toxoplasma gandhi are you using? And so if you read the popular literature, they're like, oh, man, rodents who are infected, they're attracted to cat urine. But at the end of the day, the answer is much more complicated. Sometimes we see the effects, sometimes we don't. At the moment, we don't really understand why.
And even if the story we're true, the explanation would be that the parasite wants the rat to get eaten by a cat because it wants to get back into the cat's gut for more reproductive.
Sexy time exactly. And then here's another problem. So I was talking to one of the people who did the original fatal feline attraction study, and I asked, when are we going to see a study where rodents get infected, we confirm that they're now more attracted to the smell of cat urine, and then we release them into an environment with cats and we see if that actually gets them eaten, because right now we've got this story that sounds super convincing, but we haven't actually shown it gets them eaten. And her response was like, look, I would never feel comfortable doing that to rodents. That's mean to the rodents. We don't want to be infecting cats. I don't want to have anything to do with that study. And I think it would be hard to get past an institutional Animal Care and Use Committee, which is the organization that has to approve all of the experiments that people at universities do. And so we don't actually have that study. We don't actually have that connection. And you can imagine that, you know, rodents who spend a lot of time really examining an area where there's a cue about a predator get a really good sense for like, Okay, here's where the predator seems to go. Here are the hiding places in the area. Maybe they're just like really understanding the area, and when a cat shows up, they know how to get out of there better then another rodent who happens to be passing through. And I don't know, I'm just making up stories now too, but The point is we're all just making up stories.
The point is you're saying it's not so simple as just rats who are attracted to cat here and get eaten more. You're saying you could plausibly come up with a scenario where it actually prevents them from getting eaten more, and we actually need to go out and measure this in the world. I think that's a huge lesson, right, Like we're always attracted to these simple stories and science and all of our science are stories. But just because the story makes sense to us, doesn't mean it's the way the world works. Right. We have to always go out and do experiments and make measurements because the universe is filled with surprises. Usually it's the kind of stuff we're so certain about that turns out to be wrong.
And there have been some examples where we had this great story and we thought it made sense, and then when we did dig in a little bit more, it fell apart. The behavior was not benefiting the parasite in any way. So you do have to test these stories. And I just want to tell you about one more study that I think is the closest we've gotten so far to trying to provide support for this, and this is an indirect study that was done in Switzerland. So essentially, there was this survey where people were asked like, okay, when your cat catches something and they bring it home to you, and they like, put it on your doorstep, put it in a plastic bag, and bring it to us. So they got this big collection of rodents that had been killed by cats, and then they took blood from all of these rodents and they looked to see what percent of them were infected by the parasite, Okay, and what they found was that for European water bowls, eleven percent of them were infected by the parasite. So let's walk through a really quick thought experiment to decide if we're impressed by that or not. If one percent of the poppylation of European water voles is infected and eleven percent of the European water boles that are caught by cats are infected, then that suggests that at least the infected water bowls are selectively more likely to be killed by cats. If eleven percent of the water bowls are infected and eleven percent are being killed by cats, that's just kind of random. You'd expect that from a random draw of the population, So possibly the parasite isn't changing behavior at all.
You're saying, if bowls are caught by cats more often than their prevalence in the natural population, that suggests that there's something making it easier for them to be.
Caught exactly, And that doesn't necessarily have to mean that it's because the rodents are attracted to the smell of cat urine. It could be because when you've got cysts in your brain, you run into trees or something like that, so totally different. But they looked at water voles in another population and they put out traps and they found that the percent of those water bowls that were infected by the parasite was zero. So if you assume that just about throughout all of Switzerland, most of the voles are not infected by Toxoplasma gandhiy, but eleven percent of them coming home in the mouth of a cat are, then that does suggest that they're more likely than you would expect to be getting caught by a cat after they're infected.
So the cats are catching the ones that are infected more than they're catching the ones that are not infected.
They're still bringing home more uninfected individuals because there's probably still not loads of individuals who are infected by the parasite in the environment. But of the population of les that are out there, the ones that are infected are more likely to get caught by cats than the ones that are uninfected.
But these are water voles, like swimming around in lakes.
They don't spend all their time in the water. I think they tend to be like associated with aquatic habitats.
I imagine like Brazilian voles, or like on the beach all the time or something. I want to make a connection to the human studies. But you know, that's just me trying to tell a science story.
Yeah, I'm not sure that's supported by fact, but yeah, so, I mean that's intriguing at least evidence. But I still feel like that's not a slam dunk. So that's where we are right now. We've got this cool story about zombies. The evidence suggests that there's something happening. We know it's in the brain that's enticing too, but we haven't really locked up a bunch of loose ends that we have to you know, slam dunk. Say this is definitely the parasite manipulating rodent behavior to its own benefit. So there's a lot of work left to do, all right.
So we know that this thing is out there, we know it's infecting a lot of rats and other rodents. We understand that it might be changing behavior, and it might be changing the behavior of rudents in such a way that gets them caught by cats more often, does it also change the behavior of the cats or the cats just the host for reproduction?
The cats are just the host for reproduction, and in general, the hosts where the sexual reproduction is happening, we don't often see a lot of behavior changes in those hosts. We usually see behavioral changes in the hosts that need to get eaten by those predators where the sexual reproduction tends to happen.
And so tell me how this story then became so prevalent in the popular media. There's a very simple story about how this affects you and changes your behavior and doctor thought you're a zombie. The science is much more complicated and fuzzy, as it is always was there like a seminal paper that overstated its claims, or like one particular news coverage that misunderstood this or how did this get centered in the popular mind is like the zombie parasite.
So there was a seminal paper. It was a Burdoi at all two thousand, I think, and they were the ones who identified fatal feline attraction. And it was a good paper. The science was good. Sometimes you do find this effect, sometimes you don't. They found it, and I think that kind of blew up. And then Yaroslav Flager's work suggesting that maybe it impacts human behavior too, came out, and I think a bunch of people got excited. And it could just be random chance that the first couple papers that were looking for an effect hit on something, and that's the story that made it out into the wild. And in general, you know, the first study that finds a cool effect is going to get a lot of press. The second study that says they didn't find an effect people don't usually want to talk about that. I did work in another system that found that the effect of a brain infecting parasite of fish on the fish's behavior is like way less than we had previously thought. No one cites my paper. They cite the first paper where the effect was huge.
So even as a scientist. You're throwing cold water on theories, not just in your popular science communication.
I didn't think this was going to be my niche. I didn't want it to be my ditch. But yes, that is the person that I am. So you know, call me up and invite me to your parties if you want to make sure they don't get too rowdy.
Well, you know, maybe the journalists that covered those papers they were infected by the parasite, and the parasite influenced them to write like hyperbolic statements about it because it just wanted to be famous.
And that is the fun thing about talking about this system. You always get new hypotheses and fun conversations. And yeah, it's just exciting to think about. But you know what else is exciting to think about?
What's that?
Ghosts? Oooooooo, it's as spooky as not having a enough dude. Let's take a break and come back and talk about the physics behind ghost busting. And we're back, and now it's Daniel's turn to tackle ghosts. All right, Daniel, tell me about the science behind ghost busting, and don't disappoint me because when you first mentioned this topic, I'm like, oh man, every once while you have a conversation with someone and you're like, ah, I thought I understood you, But you believe in ghosts, and that's fine, but that's not what I would have predicted.
I've had that experience, I know, yeah, and I never quite know how to approach that. I'm like, wow, okay, how do you hold this in your mind? What is it you believe or is this in some sort of portion of your where you don't apply the same sort of like rational careful thinking that I know you apply in the rest of your life. I try to always approach you sort of generally and carefully to keep the lines of communication open.
Yes, you know, I usually just transition to my listening face and I stop asking questions, and I'm like, I am listening. There are some questions science can't tackle, and I will just listen to you now. But okay, tell me about how have people attempted to use scientific techniques to answer questions about whether or not there's ghosts?
Mm hmm. Well, first of all, I want to applaud folks, because while there's a lot of stories about ghosts out there, there are people out there who are trying to sort of nail this down from a scientific point of view, just the same way like you can talk about esp and you know, pircognition and whatever, and the right thing to do there is to do experiments like can people predict what card you're holding in your hand? Can people predict the future? Like, as we were saying earlier, you got to keep an open mind because the universe is crazy and it will surprise you, and you can't hold on to pre existing narratives. You've got to be open to it. But the way to learn about the universe is not to just tell crazy stories that some parasite in your brain is telling you, but to go out there and do experiments. So while there's a lot of like spooky silliness out there about ghosts, there are also folks out there who try to see is there something we can detect scientifically? Are there sensors we can use to discover the physics of ghosts? If they are real, If they're out there, you know, that means they're part of the universe, which means they're physical, which means we should be able to detect them. And predominantly from my research by watching ghost hunting television shows, which I did for this podcast, people use basically electromagnetic field meters, Like they have these EMF meters that measure electromagnetic radiation, So you can use this if you're curious, like how much cell signal am I getting my house or whatever. Electromagnetic Radiation is just like a kind of light. You know, light is a wiggle in the electromagnetic field. Light is electromagnetic radiation. It's a very broad spectrum, all the way from radio waves with very long frequency up to extra rays and gamma rays. This are not weird and spooky in any way, Like we know what electromagnetic radiation is, but there's the thought that maybe ghosts create electromagnetic radiation or are themselves ripples in the electromagnetic field, because you know, the electromagnetic field is important to life. You and I both have a lot of electrochemistry going on, and so that's one way people try to like use science to see is there anything actually out there going on?
Is there an explanation for why we think that the electromagnetic field, which we know living organisms give off, why would we expect the dead to also be doing that? Like why is that the thing that we're looking for?
M hm, I don't have an answer, But I do have a hypothesis. Okay, First of all, we don't know what ghosts are, right, So in order to predict that they're making some physical impact, you have to have a physical model. You say, ghosts are this or ghost are that here? You have to sort of work backwards and try to say, well, if how could ghosts create this kind of signal? And I don't have an answer for you. It's true that the doctromagnetic field is capable of carrying information, and that information is massless, right, photons have no mass, And so imagine like I took Kelly, and I broke her down into her constituent bits and extracted all the useful Kelly information, the pieces that made Kelly Kelly, and not like the details of your toenails, but just like your mind and your thoughts. You can imagine making that digital the way people imagine you could like upload your consciousness into a computer and you could encode that in photons. So you know, I could take Kelly, tear you apart into your information, convert you into photons, beam you through space. Would that be ghost Kelly? I don't know. Maybe could somehow you know people's thoughts and ideas which we don't fully understand, of course, be transmitted into the electromagnetic field. I don't know that's sort of the direction people are going. I think what's really happening here is that people are trying to be creative about ways we could identify ghosts, and they're looking for the sensors we have at hand. And it's easy to get an EMF meter, like they're cheap, they're reactive. And here's my hypothesis is that old houses have bad wiring, and when you're in an old spooky house, you're gonna measure em fields or fluctuations in the electricity and you're gonna go, oh my god, look we just saw something. I have no data to support this, but that's my hunch.
If someone said, Okay, Daniel, we're giving your lab five million dollars to do the best study you can think of to look for the existence of ghosts, what would you measure or who the heck knows?
That's a great question which I'm shockingly unprepared for. I think if you gave me that money, I would try to find some location where people are reporting sort of paranormal activity that we couldn't explain and then take as broad data as we could so yeah, including ef meters and other kinds of things, to see if we can make some coral between the data we're collecting and people's experience, and that way we could start to get a handle on the physical phenomena. If there are indeed any that are connected to people's personal experience. I don't know. We do know that there's some connections between electromagnetic fields and people's experience. You know, there are these crazy studies where a psychologist created what he called the God helmet, where he created his helmet and he put very strong electromagnetic field emitting coils in the helmet and he put this on people and he turns it on. So basically he immersed your brain in a strong electromagnetic field. And he reported that once the helmet was activated, the wearer's temporal lobes their brain were pounded with these fields, and eighty percent of the people who wore this helmet reported feeling quote a presence of some kind in the room with them, including on some occasions visions of God. So you know, we know the brain is made of neurons, and neurons are electromagnetic. They send little pulses of signals, and so it's not crazy to imagine that if your brain is immersed in a strong field, it might change the way that it behaves. So now we're talking physics zombies, right, and it changes the way people feel, what they experience and what they see. So it could be that if you're in a crazy old house with strong electromagnetic fields, those things change the way your brain behaves. Plus you're expecting to see something sort of weird. There's a lot of psychology and physics going on here, So it could be that that's a physical phenomena that could connect people's experience and like readings on an EMF meter.
And so I assume that this guy set out to disprove that there are ghosts and just showing that you can create this with EMFs, not to show that EMFs are the way that we communicate with the undead.
Right, Yeah, exactly. I don't think he was saying that God is electromagnetic. No, he was saying that our perception of reality is influenced by electromagnetic fields in a way that it could make you feel like spooky or haunted. And so you see a lot of EMF meters on TV with ghost hunters, and I'll say that this is TV show called the ghost Hunters, and they're always showing up at these spooky houses looking and they never see anything. There's never any readings on the meters that are useful or interesting or conclusive, you know, which is probably why the show keeps going because if they found ghosts, they would be done, Oh yeah, we found it, show over, so it would ruin the drama.
So I think in those shows they also say something like, oh, the temperature drops suddenly, what do we know about that?
Yeah. Another popular technique is just like gathered data about the temperature. So there are these meters you can buy. They're called kestrel meters. Again, they're cheap, they're effective, so a lot of people have them, and they can do things like detect change in airflow or temperature or barometric pressure. They're very useful for understanding weather and like it's a tornado coming. And some ghost hunters believe that like a sudden drop in temperature is a sign of paranormal activity. There's no actual data to support that. Nobody's actually found a correlation between people's reports of paranormal activity and temperature dropping. But you know, it's another thing we can detect about our environment, and it's the kind of study I totally support, Like, let's keep an up in mind, let's go out there, let's take physical data rather than just say I saw a ghost in the corner. Yeah, because even if people believe stuff, eyewitness reports are very very hard to use scientifically because, as we know, they're influenced by memory and emotion and all sorts of stuff.
Okay, So I have been dying for us to get to the point where we get to talk about Ghostbusters because when I was a kid, I was obsessed with Ghostbusters. It's possible that my first crush was on Egon Nice, the character in the cartoon. So how good is the science there. They've got those proton packs, they can like catch them in that box and store them in that container. What is the science there?
Yees? So I love Ghostbusters and it's not hard science fiction, but I do like that they dress it up a little bit sciencey, you know, and the scientists are kind of heroes in that story. They're creating technology, they're understanding it. They're not just running around.
And being woo woo very handsome too.
Yeah, exactly, they're good looking, they're charismatic. So what's going on with the science Ghostbusters? While they have these PKE meters, you know, which detect psychic activity. pKa stands for psychokinetic energy, and I think this is just like a fancy version of an EMF meter. They invent this device, they don't go into the details, like what exactly is it measuring? How is it detecting psychic energy? I think it's basically inspired by real life EMF meters like measure fluctuations in the electromagnetic field.
So there is no actual such thing as a pKa meter.
No, it's just a prop you know, it doesn't actually do anything. There is no psychic kinetic energy as a physical concept. That would be awesome. Wow, somebody could invent that that detected this new field of energy, like huge, huge discovery about the nature of the universe.
That would be incredible.
But my favorite part about Ghostbuster science are the proton packs.
Well, all right, but clearly those would work, right.
Those would work in some sense, Like what is a proton pack? If you look at the picture on their backs, they have these circles on them, and what they're really doing there is they're creating a little particle accelerator. Like what do we do with the Large had Drunk Collider. We take protons, we speed them up, We bend them around in a circle so we can keep speeding them up many many times, and then we smash them into stuff. That's what a proton pack is. Takes protons, it spins them around, it shoots them out. It's basically a proton beam generator. And the science of that is pretty solid. Like we build those things, we have those things in real life. I have some comments about like the size of those things on their backs, but like those are details.
Do you think one day we could shrink them down enough that you could actually fit them on your back.
You could definitely have a proton pack small enough to put on your back. The question is could it have enough energy. The reason the Large had Drunk Collider is so large is that when protons are going really really fast and they have so much energy, it gets harder to bend them. So you need super powerful magnets. At the Large had Drunk Collider, we have like amazing souper conducting magnets that are really awesome, and they can just barely bend those protons around in a circle that's like thirty three kilometers, So to get them within like half a meter at very very high energy would require incredible magnets, which would also be pretty dangerous, like you'd be walking through the streets in New York and like everybody's keys would be flying out of their pockets and like killing people. So very small would require very high magnets. So that part I'm a little skeptical of. The real question is could you use a proton beam to somehow capture ghosts?
Okay, so how would that work? What would that have to say about the ghosts in order for this to all work out?
Yeah, exactly, Well, protons are positive, so you're shooting a beam of positive charges and you're somehow hemming the ghosts in with that. I mean, in the show, the beam doesn't move perfectly straight. It's sort of like a whip, more like Wonder Woman's lasso or something, which is definitely not scientific, like the protons would move in a straight line or be bent by a magnet. But I guess if ghosts were like negatively charged, you know, some know, then they would get attracted to the beam and you could like stick the beam to them and even pull them around with the beam. So yeah, if ghosts are for some reason negatively charged, then protons are the right way to hem them in.
So next year at this time, we'll be reviewing the science about whether or not ghosts or negatively charged, because people will probably follow up on your work here.
Well, if ghosts were positively charged, you could just use an electron beam to capture them, but then you got to know the charge of the ghost before you shoot the beam at them, right, So you could do it either way positive or negative, and new restriction there.
Gets very complicated, So let us know if you have any data on this question. But actually, Barry Rich wrote a really great book where she interacted with the community of people who ask questions about this kind of stuff, and I highly recommend every book ever written by Mary Roach.
She's excellent.
Yeah, okay, everybody, Happy Halloween. We hope you have an amazing spooky day, and if you want to send us any questions or suggestions for future shows, drop us a line at Questions at Daniel and Kelly dot org.
Happy Halloween, everyone, and this episode goes to show you there's science in everything, in me and you and even in Halloween.
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