Dreaming: Why we hallucinate while asleep (and do spiders do it too?)

Tiny Matters

 A recent study looking at sleeping spiders left Sam and Deboki with a lot of questions, namely, “Do spiders dream? And why do we humans dream?” In this episode of Tiny Matters, you’ll hear all about dreaming and its connection to sleep, and learn what big questions the field is still trying to answer.

Transcript of this Episode

Sam Jones: I don’t know about you, but I am someone who dreams a lot. Not in the ‘I have big dreams’ sense—although I would like to think I do—but in the ‘I go to sleep and my brain is cooking up dreams.’ A lot of the time I think I just remember little pieces of them, or wake up knowing that I had a dream but have already forgotten what happened in it. What about you Deboki?

Deboki Chakravarti: I usually don’t remember much about what I dream, but I’m traveling right now and had to leave my cat with my parents, it’s a whole thing, since I’m going to be out of the US for a few months, and last week I had a super vivid dream that my parents came to visit me with my cat. And I knew it was a dream while I was dreaming it, but I was still so happy to hold my cat in the dream.

Sam: Yeah I think sleep and dreaming are so interesting. So when I came across a study showing that humans and spiders might not be as different as you’d think when it comes to sleep and maybe dreaming, I had to learn more about it.

Welcome to Tiny Matters. I’m Sam Jones and I am joined by my co-host Deboki Chakravarti. At the beginning of last month—August 2022—our listener Prabarna (thanks Prabarna!) pointed me to a story in The New York Times titled, “Do spiders dream of eight-legged sheep?” Great title. Left me with a lot of questions. And like I mentioned I am so fascinated by sleep and dreaming and I feel like there’s a lot of misinformation out there about dreaming in particular and what it is and what it means and so I figured…it’s about time that Tiny Matters covered it.

Deboki: Today on the show, in addition to hearing about spider sleep and possible spider dreaming, we’ll talk about why scientists think we dream and some of the big questions they’re trying to answer.

So back to the spiders. To learn about the sleeping spiders we called up Daniela Rößler, the lead author on the study that inspired the “Do spiders dream of eight-legged sheep?” headline. Daniela is a behavioral ecologist at the University of Konstanz in Germany and a guest researcher with Max Plank Institute, also in Germany.

Sam: Daniela told us that she didn’t start her research career studying sleeping spiders, or spiders at all. Her PhD focus was on how animal coloration impacts predator-prey relationships. She was studying things like camouflage and mimicry—for example, when a harmless animal looks like a dangerous animal to keep predators away. And she was studying this in colorful toads in the Amazon rainforest. But after her PhD was done, Daniela said she wanted to ask similar questions in a different—easier—model system, which led her to jumping spiders. A big reason these spiders were easier to work with was that Daniela didn’t need a permit to go to the Amazon rainforest to find them.

Daniela Rößler: I could climb out my office window and collect 50 spiders and bring them in the lab, put them in little boxes and they'll still show behaviors that are pretty much close to their natural behaviors. It is just something I could never have done with the toads.

Deboki: Daniela began with trying to understand what I think is a fascinating behavior of these jumping spiders—they mimic ants.

Daniela: They pretend to have three body segments and they actually move like ants. So they make little stops when they move and they hold up the first pair of legs to pretend they're antennae. It's really wild. It's super hard to tell them apart—you would be like oh yeah, there's just an ant, but actually it's a jumping spider disguised.

Deboki: But then the COVID pandemic hit and everyone, including Daniela, found themselves working remotely.

Daniela: COVID hit and I was basically working a lot from home, working in the backyard sort of field, and just watching local jumping spiders here in Germany and observing them. And I found so many cool things, so many cool behaviors and signals and stuff that was just not described and undocumented, and I kind of fell into this rabbit hole.

Deboki: That rabbit hole eventually led her to observe some odd behavior while the spiders slept. It all started when Daniela collected jumping spiders from around her home, put them in little boxes, left those boxes on the windowsill, and left for a few hours to meet friends for dinner.

Daniela: And when I came home, I just quickly wanted to check if the spiders are doing alright. And they were all hanging from the lids on little silk threads. And that was the most unusual thing I've ever seen because I've never seen that before. And I couldn't find anything in the literature. It was just absolutely weird. And they did that for the whole night.  

And we went to the field and we checked if they actually also hang there. And they did. It was so much easier to find them at night because you could pluck them from the vegetation like little Christmas ornaments. It was super neat. And then talking with people they were like, oh, so they're sleeping. And that's when it started. It was like, hmm, I don't know. What does that actually mean? I had no idea, it was just not the field I’m coming from.

Sam: So Daniela got a night vision camera and started watching the spiders sleep. She says they'd start off hanging from their silk threads, maybe they’d even catch a fly and have a little pre-bedtime snack. But eventually they would stop moving. And then, every 15 to 20 minutes, for a minute or so at a time, the spiders would start to twitch and their legs would begin to curl inward.

Daniela: I thought, oh, maybe this spider is not healthy haha what's going on with that one? Maybe got parasitized or something. But it appeared again and again and again, and in really regular intervals. So we thought, okay, this looks a lot like they're asleep and they're actually having some sort of dream or some experience.

Deboki: That led Daniela and her fellow researchers to wonder if these spiders could be undergoing REM sleep—or rapid eye movement sleep. REM sleep is a phase of sleep where your body is paralyzed but, like the name suggests, your eyes are quickly darting around beneath your eyelids and the neurons in your brain are firing as if you were awake.  

With people, it’s very easy to tell if they’re in REM sleep, but jumping spiders can’t move the lenses of their eyes. They do, however, move the retinas in their eyes to adjust their gaze. In adult spiders there’s too much pigment to see their retinas, so Daniela and her fellow researchers needed to get a bit more creative.

Sam: They decided to look at baby spiders, which are called spiderlings. Because they lack pigmentation, you can see spiderling retinas.

Daniela: The babies are translucent for the first 10 days. So let's film the babies and check out their retinas. And indeed, we then found that they had the exact same phases of twitching and curling of the legs. And always when it happened, the eyes were moving. And so, bingo.

Sam: Knowing that spiders are going through REM sleep like we humans go through REM sleep is very cool. But…how does that relate to dreaming? Well, REM sleep and dreaming have a history of being linked. But Caroline Horton, a professor and sleep researcher at Bishop Grosseteste University in England reminded us that dreaming doesn’t always accompany REM.

Caroline Horton: We often associate the dream experience with rapid eye movement sleep. And that is an association that's really well ingrained. And it's maybe true in 60, 70% of cases, but there are absolutely many cases of people reporting dreaming outside of rapid eye movement sleep, in the deeper stages of sleep, and also people can often experience rapid eye movement sleep and not remember a dream.

Deboki: So you’re not necessarily dreaming during REM, but you can be. Which makes you wonder: when those baby spiders were experiencing REM were they also dreaming?

Caroline: One thing that we think in humans is a prerequisite to dreaming is this idea of a cognitive self. So you need to have an understanding of you, yourself in place and time in order to be able to experience that awareness of yourself when you're dreaming.

Now, when we’re dreaming, we have a suspension of reality monitoring. So we just accept what's happening really, as if it is true. Only when we wake, do we know that ‘hang on, I was asleep, that wasn't real.’ But in order to have all of that cognitive capacity and metacognitive capacity to reflect on that, we do need to know a little bit about ourself. In something like a dog or a cat or a rat with, you know, a brain structure that certainly has some similarity to a human brain, we don't know if they have that ability to recognize their self in their memories. So I would be surprised from my rudimentary knowledge of spider brain structure, I'd be surprised if they had that capacity. But who knows, who knows. It may still be that they are going through these emotional changes and that's beneficial for them. They may even be acting out some kind of scenario that they have experienced before, but do have a conscious recollection of it? And that's the key definition of a dream. I would imagine not. So they may still have those behavioral benefits, but maybe they’re not actually dreaming.

Deboki: Let’s talk about some of those behavioral benefits. Why do we dream?

Caroline: I wish there was agreement in a clear answer. I mean, my hunch is that there isn't one purpose or function of dreaming. It's evolved to coincide with sleep because, as humans, we think that we sleep for many reasons and that sleep is so beneficial to our health, physically, mentally, in just about any way that you can think of it. We assume that the psychological side of that coin maybe has multiple functions as well.

What we do know is that while we are dreaming, we are processing emotions. So we think that there is good evidence behind the idea that we need to play out some pretty scary scenarios whilst we're in a relatively safe space. So we're paralyzed, we're tucked up in bed. We're not physically acting these out, but mentally we're giving ourselves the opportunity to simulate some scenarios that we hope we won't need to experience in life. But if we do, we've already had an opportunity to engage with them. So there's a kind of survival rehearsal, simulation type theory of dreaming.

Sam: Caroline says we might also be regulating our emotions by experiencing what are sometimes extreme highs and lows. I mean think about a really fun dream you’ve had, or a really scary nightmare. There’s a lot going on.

Caroline: After we've had a chance to engage in a decent uninterrupted bout of REM sleep our emotions are more regulated. So we can probably recognize that when we don't sleep enough, we're edgy, we're moody.

The context of dreaming is very much like a psychotic episode. You know, we don’t know what's real and what isn't, we are tuned into and convinced by these hallucinations that are strongly visual, strongly emotional, and we just believe them. So it's crazy and yet it's perfectly normal and we assume that we need to experience the crazy in order to regulate our emotion and go about our daily lives when we wake up.

Sam: I think this is just so cool. I mean, how nice to work through a bunch of stuff when we’re asleep so that we wake up in a better mood. Who doesn’t want that?!

Now that you’ve heard a bit from Caroline about the possible importance of dreaming, you might be wondering… how does one get into dream research? Because it’s definitely something I asked right away when we talked.

Caroline Horton: The first thing that interested me in dreaming was what we in psychology term individual differences. Essentially, why do some people remember their dreams and some people not remember their dreams? So I started looking at individual differences and that led me to looking at the characteristics of dreaming. So what is it about the dream that means you remember it, rather than the person? We soon realized that actually dreaming is universal. The differences between people are not as great as you might think. So that has morphed and changed over 20 years or so for me into looking now much more at the mechanisms of dream memory—what are those memory building blocks that allow us to understand that whole fantastic experience that we know is a dream.

Deboki: In talking with Caroline, we pretty quickly realized that studying sleep is tricky, but studying dreaming is difficult on a whole other level. In part because you have to rely on humans to tell you ‘hey, I was just dreaming’ and we all know humans are not always reliable. And Caroline says that past studies of dreaming make it hard for some people to take this work seriously.

Caroline: The study of dreaming predates the science of dreaming. So the interest in dreaming is kind of long established from early philosophers and then Freudian ideas that maybe dreams reflect these unconscious wishes. As a result, dreaming and the study of dreaming is often associated with there being a symbolic language of dreams that a psychologist needed to uncover, and that really taints the scientific viewpoint. So it's really hard to try and push that aside and say, as a scientist, what we want to do is approach things in a systematic way, because it's not uncommon for people to say, ‘dreams are bit crazy, and the people are interested in these things are probably unscientific in their approach,’ so that is a challenge to overcome before you even set foot in the lab.

Sam: Caroline says psychology and neuropharmacology—changes in brain chemistry—could be a powerful combination for understanding why we dream and how dreaming affects our bodies, but for the most part that data just doesn’t exist. There is, however, a good amount of understanding when it comes to the chemicals that move us from one sleep state to the next. For instance, cortisol, which you’ve maybe only heard talked about as a stress hormone, in the context of fight or flight. It has a bit of a bad reputation, but Caroline says that’s not really fair and that we should shift our thinking to it being more of a ‘preparedness’ chemical.

Caroline: The cortisol awakening response underpins our ability to come out of sleep and be ready to fight the day. So we know that we have peaks of cortisol during some of these eye movement periods as well. So it seems like, okay, we need to experience that in order then to help us be extra ready when we wake up. So I think cortisol is something that is a little bit misunderstood, but if we think of it as being fundamental in that sleep to wake shift, it helps us think of it as a readiness chemical rather than just a fight or flight or stress hormone.

Sam: Oxytocin is another chemical our brain produces that Caroline says people have tried to associate with specific instances of social interactions in dreams, but the data there are limited.

Caroline: So if we think of oxytocin levels as increasing when we are having those cuddly moments or those particularly pleasant interactions,  we might assume that we would see real time changes or increases in oxytocin that would correlate with the particular dream content that reflects those social scenarios. I think it's methodologically hard to demonstrate, and that has hampered the ability to demonstrate that that relationship exists. I think that relationship does exist, but what we need to nail first is the tools by which people can accurately report their dreams.

Deboki: Today, Caroline’s research heavily focuses on how dreaming benefits your memory.

Caroline: What we think is happening when we are dreaming is that we are experiencing things from our waking lives, but we are not experiencing in the same ways as we would do when we're awake. We're getting all of the cool bits, we're mixing them up. And we think that this has function within this whole idea of memory consolidation. So we think that having the ability to fragment our memories, combine them, create new things out of them is all part of the memory filing and storage process.

Deboki: And if memory is something that you want to dive into after this episode, definitely check out Tiny Matters episode 5 titled ‘What is a memory?’

Sam: We’re big fans of shameless self-promotion on this podcast.

Deboki: Yes, absolutely.

Caroline: We've all been affected by the pandemic in different ways. And there's been just a massive shift towards trying to focus on sleep health and sleep hygiene. So where I’m shifting toward now is trying to look at whether dreaming changes when you try to improve your sleep. And I think that's fascinating. I think it would be a way of trying to demonstrate that there could be some benefits to dreaming. People who tend to remember their dreams are probably sleeping quite well. And even if people are remembering negative dreams, actually there is a positive to that—they're sleeping sufficiently to enter into those sleep cycles. If people say they never dream at all, or never remember their dreams at all, there's a chance that they're not sleeping enough. So I just think there's a chance to use, you know, our, our understanding of improving sleep and the importance of sleep hygiene to bring in the importance of dreaming as well and actually say that there is a positive to it. We don’t have to be wacky dream interpreters in order to recognize that giving our mind the opportunity to experience some crazy scenarios can actually help us be more regulated when we function in the day.

Deboki: I love that. I mean, I’m not a fan of nightmares, but I like the positive spin on it. Remembering a bad dream could just mean you slept well. Speaking of bad dreams, I would bet a lot that at least one of our listeners has had a bad dream involving spiders.

Sam: Yeah, I’m sure. Poor spiders, they get a bad wrap. Daniela, who we spoke to earlier in the episode, says she doesn’t love the reporting of spiders dreaming because we only know they experience REM, we have no idea if they’re dreaming during REM. But the upside to that reporting is that maybe people will be less likely to kill a spider the next time they see one. Because how could you kill a little dreaming spider?

Daniela: A lot of people in my family didn't like spiders when I started working with them. I don’t think they're all in love with spiders now, but they definitely come to appreciate them. And I think jumping spiders are the entry spider. Like if you're afraid of spiders and, but you overcome that fear and you manage to Google the term ‘jumping spider’ you look at those cute faces and it’s really hard to be afraid of them. I think that's why jumping spiders are so popular because they are very approachable. They have super cute eyes. They don't behave anything like a spider in the ‘basement spider’ sense. They're very predictable in their movements. I think what makes spiders uncanny for a lot of people is the way they move, like eight legs already is just six too much for us. And it seems like they're not easy to predict what they're gonna do next and where they're gonna go. With jumping spiders, it’s different. They just feel like cats, you can see them look around, you can see them think you can see how they look at you. You'll just see that they're not your normal spider and they're super freaking cool.

Sam: Alrighty, let's Tiny Show and Tell.

Deboki: Cool. Let's do it. Today I want to talk about rabid raccoons.

Sam: Ooh.

Deboki: Because I read this really interesting article in The Atlantic by Sarah Zang called America has a Rabid Raccoon Problem, and it's had one for decades. This outbreak goes back at least to the 1950s. There was a rabies outbreak. It started with the raccoons in Florida, and then apparently it might have spread because people shift these raccoons out without realizing, I'm hoping that they had rabies. They were sending them to hunting preserves in other states. And so then the outbreak spread from there. So the outbreak has been going on for a while. But one of the challenges the government had that they talk about in this article is that even though the rabies isn't great, the rabid raccoons aren't great, people don't necessarily like the idea of killing raccoons.

So the government had to figure out what to do, and they did the next best thing. Actually, maybe the even better thing because it doesn't involve killing raccoons, which is to vaccinate them. Now, how do you vaccinate a raccoon? Apparently you use little flavored ketchup packets that are just oral vaccines flavored with fish meal. You basically have to trick the raccoons into taking these oral vaccines, and it's done a really good job of helping to lower the overall spread of rabies. So this has been going on for several decades, and one of the moments I really love from this article is when one of the people who's involved with this project talks about how their goal is really to get raccoons rabies free by 2063. So it's definitely a long term thing.
But I really, really recommend people check out this article if you're interested at all in this, in combination with the work that went into developing the vaccines. There's also the work that went into, "How do we get the raccoons to take them? How do we make it appealing to them? And then also how do we deliver them?" There's apparently planes with little treadmills in them that you use to distribute them. Like a little conveyor belt on the end of these small airplanes.

Sam: Oh.

Deboki: So I think you just kind of send them down. There's also other issues in terms of they want to make sure it gets to the raccoons, but they don't want other animals to be taking these vaccines because they don't need them. They really want it focused on the raccoon. So how do you design, I guess, basically a little vaccine trap that's just like raccoons couldn't get into, but not other animals. It was very fascinating.

Sam: That's cool. I'm excited to read this. That's so interesting. I had no idea.

Deboki: Have you ever seen a raccoon live? Sorry, this is not a scientific question.

Sam: Yeah, I mean, so growing up in the burbs outside of Boston, we definitely had raccoons around. I remember as a kid turning on a porch light and looking outside and seeing a raccoon trying to get into something that we had left outside accidentally. So I've definitely seen them in person. And they are kind of cute, but they're also, I do find them a little bit creepy. I think I would read this, not because I dislike raccoons, but I think I'd be more interested in the science angle than the fact that it's a raccoon.

Deboki: For sure. Yeah, I remember the first time I ever saw a raccoon live, it was like 5:00 AM in Boston, and I was walking super early to the gym, so I was still not awake, and I saw it and I thought it was just like a giant cat at first. And I was like, "I've never seen a cat this big." And then I realized that I was staring into the eyes of a raccoon. Luckily it was not rabid.

Sam: Yeah. Well, thank you Deboki. For my show and tell, I'm going to talk about the oldest surgical amputation known.

Deboki: Wow.

Sam: So in 2020, researchers excavated remains from a grave inside a large three chambered cave on the Indonesian island of Borneo. The remains appeared to be of someone who would be around adolescent age. And then to actually date how long ago the person lived, the researchers used radiocarbon dating of just kind of burned bits of wood that were below the grave. And then they also used another dating technique on a tooth from this person's lower jaw. So it appears that this person lived around 31,000 years ago. The person was missing part of their lower leg, but the bone had actually healed. So it indicated that a hunter gatherer society, it was 31,000 years ago, performed the operation with enough skill that the kid or the adolescent actually lived another six to nine years after the surgery. So they didn't die from some sort of infection or blood loss, which would've been pretty common. I mean, this was a very long time ago.

Until now, the oldest known amputation was in remains that are of a farmer in France whose left forearm was removed about 7,000 years ago. And then in North Africa there have been findings of skulls where it looks like openings were created maybe 13,000 years ago. But again, this is almost 20,000 years before that.

Deboki: Wow, that is fascinating. Yeah. It's always so fascinating to hear when we date these old things and it just pushes back, when was the first amputation? When was the first this kind of surgery or the first human behavior or whatever of this type? And it just always feels like it's earlier than we thought. It's always so much earlier than you can possibly imagine.

Sam: Thanks for tuning in to this week’s episode of Tiny Matters, a production of the American Chemical Society.

Deboki: This week’s script was written by Sam who is also our exec producer. It was edited by me and by Matt Radcliff who’s the Executive Producer of ACS Productions, and was fact-checked by Michelle Boucher. The Tiny Matters theme and episode sound design are by Michael Simonelli and our artwork was created by Derek Bressler.

Sam: Thanks so much to Daniela Rößler and Caroline Horton for chatting with us.

Deboki: If you have thoughts, questions, ideas about future Tiny Matters episodes, send us an email at tinymatters@acs.org.  

You can find me on Twitter at okidoki_boki

Sam: And you can find me on Twitter at samjscience. See you next time.