I Dream Of Octopuses, But Do They Dream About Me?
Sleep is nearly universal in the animal kingdom, but how animals sleep is not the same. Studies have found that in mammals, giraffes get the least amount of shut eye, while koalas can sleep up to 22 hours a day.
There are also different types of sleep cycles—including a stage called rapid-eye movement or REM, which is often compared to non-REM sleep. A team of researchers wanted to study these different sleep cycles to understand how they might be connected to learning and memory. The scientists turned to the octopus as their study subject, selected for their complex behaviors and large brains. Their results were recently published in the journal iScience.
Neuroscientist Sidarta Ribeiro, one of the authors on the study, joins Science Friday to explain how you measure the sleep cycles of an octopus, and what this can tell us about if an octopus might dream.
Invest in quality science journalism by making a donation to Science Friday.
Sidarta Ribeiro is a professor of Neuroscience and the vice director and founder of the Brain Institute at The Federal University of Rio Grande do Norte in Natal, Brazil.
IRA FLATOW: This is Science Friday. I’m Ira Flatow. Birds do it. Bees do it. Yes, even octopuses do it. I’m talking about, of course, sleep. Sleep is nearly universal in the animal kingdom. But how animals sleep is not the same. Studies have found that for mammals, giraffes get the least amount of shuteye, and koalas can sleep up to 22 hours a day. Oh, to be a koala.
Then there are the different cycles of sleep, like REM versus non-REM sleep. A team of researchers studied these different sleep cycles to investigate how they might be connected to learning and memory. And they turned to the brainy octopus, of course, as their study subject. The results were published in the journal iScience, and my next guest is one of the authors on that study.
Sidarta Ribeiro is a professor of neuroscience and the vice director and founder of the Brain Institute at the Federal University of Rio Grande do Norte in Natal, Brazil. Welcome to Science Friday.
SIDARTA RIBEIRO: Thank you very much, Ira.
IRA FLATOW: Tell me why you study an octopus, for example, rather than a shark or some other kind of animal.
SIDARTA RIBEIRO: OK, so most of my research has been performed in mammals, in rodents and in humans. When I returned from the United States to Brazil after my PhD and postdoc to begin my lab, I said, I will begin studying octopuses as well because they have such complex behaviors. They have such a big brain. We could probably learn something about the constraints for brain design if we study very complex animals that are very different, like, say, the rat and the octopus.
And then for many years, I was looking for the right collaborators. I teamed up with [INAUDIBLE], who’s a biologist, a specialist in octopuses. And then she found Sylvia Medeiros, the now graduate student that carried most of the work. And it’s been an amazing ride. We discovered that octopuses have something similar to REM sleep. They have what we call active sleep that occurs very precisely after every 30 minutes, with a very precise interval. And it’s always coming after a long episode of quiet sleep.
And the distinction between the two kinds of sleep is very dramatic. During quiet sleep, the animals are completely pale, with the pupils closed, not moving their arms, and really in a very quiescent manner. And then when they transit into active asleep, they become seemingly agitated. The colors change dramatically. The textures of the skin change dramatically. The eyes move around. And still they are unresponsive to sensory stimulation. We tested the animals while they were in different states, and we found that those two states, quiet and active sleep, are states of unresponsiveness to sensory stimulation.
IRA FLATOW: Now, I know that octopuses have this great talent for changing their color and their shape to avoid predators. Do they sleep this way, or are they not able to do that while they are asleep?
SIDARTA RIBEIRO: Well, so this is the thing. When they are in quiet sleep, they don’t change any of that. But when they are in active sleep, they change all of that. And this is what we quantified using some computational strategies to work on the images that we recorded for very long hours, and then we crunched the numbers to really establish that those sleep states are quite distinct.
For example, we found that the active sleep state, which is analogous to REM sleep, will only occur after very long episodes of quiet sleep, episodes that are beyond six minutes. And when active sleep kicks in, it’s always a short episode, below one minute. So it’s something that is very fleeting but occurs quite precisely every 35 minutes.
IRA FLATOW: Is the sleep modality you see in the octopus– the REM, the awake, the different kinds of sleep– the same thing that’s going on in humans?
SIDARTA RIBEIRO: Well, we think it’s similar. Whether it’s the same thing– it’s highly unlikely that it’s the same thing because these animals are quite distanced in terms of evolution. If we are to think that this is the conservation of an ancient trait, we will have to go back 500 million years ago. So this is probably a case of convergent evolution. We’re probably right to say that the sleep cycle that consists in going from a quiet sleep episode towards an active sleep episode is something that evolved twice, or even perhaps more times, because perhaps Drosophila, the fruit fly, also has it.
And it’s probably related to the complexity of the wiring of the brains of these animals. Most likely, we’ll see a similar phenomenon that has different underlying mechanisms.
IRA FLATOW: How do you know when an octopus is sleeping? I’m guessing they don’t snore.
SIDARTA RIBEIRO: So in our case, we confirmed that they were sleeping by stimulating them with images of crabs that they would prey upon shown on a screen or using a vibratory stimulation test, which we hit the aquariums lightly with a rubber hammer. And this was something that they could not notice. They wouldn’t react to these kind of stimuli when they were in either quiet sleep or active sleep.
But they would react very promptly to these kind of stimulation when they were indifferent in other states. So they spent about 25% of the daytime sleeping. Only 0.5% of the time is in active sleep. But either in quiet or in active sleep, they are unresponsive to sensory stimulation.
IRA FLATOW: We all know that sleep is important, but do we know really why we sleep, what’s going on there, what happens during sleep, what the function is?
SIDARTA RIBEIRO: Well, it’s interesting you ask me this because I just wrote a book on this, which will come out in the United States and Canada in August, I believe, by Penguin Random. It’s called The Oracle of Night. In this book, I argue that, yes, that we do know why we sleep, and it’s many, many layers of explanations because they evolved in very different moments and under very different selective pressures.
So some of the things that happen during our sleep are as old as animals. And some of the things that happen in our sleep are as old as the pandemic. There are many layers of complexity in terms of what sleep does to us. So sleep is super important for protein synthesis, for hormonal synthesis, for the replenishment of biomolecules that were spent during the day, for the triage of memories, if you want, the separation of memories that should be erased and memories that should be kept and memories that should be mixed and restructured to generate new behaviors.
So all that happens during sleep. There’s detoxification going on during sleep. And then there’s another level of complexity, which is the symbolic level, something that occurs not purely at the neurobiological level, but at the emergent psychological level. And then we go into the symbolism of dreams, and we go into the difference between the personal unconscious and the collective unconscious. And so we can dream about things that happen to us or that relate to our lives, but sometimes we dream of symbols that are shared by many cultures and that have to do either with our shared cultural contents or our innate biology.
So all that is compounded. And then we say, so, with all that, what is the function of sleep for us now? And I’d say for most people in the urban setting, not much. Because sleep and dreams in particular are not something we pay attention to. Sleep is under attack because of all the screens that we have in our lives, because of all the different habits that take time away from sleep, and dreams even more so.
If all that that I said has any resemblance to what happens in the octopus, we still don’t know. It’s a far-fetched comparison at this point. What we can say at this point is that they have a sleep cycle that to some extent resembles what we see in birds, in reptiles, in mammals, which is to have a cycle comprising quiet sleep, long episodes of quiet sleep, then falling into active sleep for short periods of time. This particular architecture seems to be a hallmark of octopus sleep, and it’s quite similar to what we see in those vertebrate groups.
IRA FLATOW: Is there any way to test whether an octopus is dreaming or not?
SIDARTA RIBEIRO: Ah, this is a very difficult question to address because the fact that they are having something like REM sleep does not necessarily mean they are having a complex inner life experience in which some representation of the self is undergoing lots of adventures. We don’t know that. It would be very hard to be sure of that. Of course, one idea that has been floating around in the field, and many laboratories, in one way or another, pursue it, is that we may be able to read the inner state of the animal based on the pattern shown on the skin. This notion that maybe we can read even dreams in octopuses by quantifying and investigating their skin color and texture patterns.
Within our study, we quantified those patterns, and we were able to show that they changed dynamically and dramatically during active sleep and not during quiet sleep. But to actually try to infer mental content from those patterns would be a big step, not only for this reason, but because of the fact that there are more neurons in the periphery, in the body of the octopus, than in the brain. So maybe if we can read anything at the skin level, maybe it reflects local processing and not central processing. But it could also reflect central processing. This is an open, interesting question that we want to explore further.
IRA FLATOW: That’s very interesting. I mean, if there are more neurons in the periphery of the octopus, is it doing most of its processing when it’s sleeping in the periphery instead of in its brain?
SIDARTA RIBEIRO: That’s a possibility. I actually believe it’s probably both. I believe that active sleep is important in many different species because of the what we call systems consolidation, which is memory consolidation not just within one brain region or one region of the nervous system, but actually allowing the coordination of the integration of information across brain regions. REM sleep plays a big role in this kind of integration in mammals, and it’s possible that active sleep plays a similar role in the octopus.
IRA FLATOW: Every pet owner knows this. If you watch your dog sleeping, sometimes they whimper. They look like they’re pawing. They look like they’re running in their sleep. Can you see this in the octopus at all? And am I just projecting what I’m doing and that’s not really happening in the animals?
SIDARTA RIBEIRO: Well, during active sleep, they do move their arms, and they do move their eyes, and the patterns on the skin are very dynamic. So I think the question is to come up with a quantitative and objective interpretation of those changes. Right now, we know that the changes are there. What exactly do they mean? We don’t know.
It is tempting, for example, to interpret some of these patterns as reminiscent of specific behaviors. I’ll give you an example. The octopus can show a pattern that we call half and half, in which half of the body is very dark and half of the body is very pale. And they can switch which side gets to be pale and which side gets to be dark.
This is observed. This is known when animals are awake and they are, for example, having some courtship interaction, a male-female interaction, in which the male can show one side only to the female with a certain color and the other color to the other side to the sea or to another animal. It’s also something that you can observe when animals are competing, say two males competing for territory or access to a female.
So this half and half pattern is known as a waking thing. We saw a state that we call quiet half and half, in which the animals are very quiescent and producing the half and half pattern. So it is tempting to speculate that maybe the animals were dreaming about one of those either courtship or competition encounters. However, we must ascertain that the animals were actually sleeping. We tried to do that by stimulating the animals during the state.
And we found that the arousal threshold was in between what we found for the awake, alert state and what we found for the quiet sleep state. So we could not really come to a conclusion. And this is why in our paper, we describe the state and we talk about this, but we say we are not sure whether the animals are asleep or not.
And to further complicate things, it’s difficult to stimulate only one eye of the animal and not have the other eyes stimulated when you’re inside a glass tank and there’s reflection inside the aquarium. So this may wait a little longer before we understand what it means. Another possible interpretation for this kind of quiet half and half pattern would be perhaps octopuses also are able to have unihemispheric sleep, so sleep with half of the brain, which is something that is observed in some aquatic mammals and also in birds and sometimes has to do with the fear of predation, in addition to the need to swim and go to the surface and breathe, like in mammals, in aquatic mammals.
So it is possible that the octopus has something like unihemispheric sleep. But again, we are far from knowing the answer right now. What we have is a bunch of new questions, which is great.
IRA FLATOW: This is Science Friday from WNYC Studios. One last question for you. As you mentioned before, your lab is in Brazil. What is the state and safety of science there now?
SIDARTA RIBEIRO: Science is in intensive care and with no oxygen. The Brazilian government is anti-science. It does not believe in vaccines. It does not believe in wearing masks. And it does not believe in science. We should have been producing the Brazilian vaccine and perhaps selling it to our neighbors. And instead, we’re trying to buy it, and we can’t buy it because we didn’t buy it at the right time.
We only have 5% of the Brazilian population vaccinated. Right now, just yesterday, we had 3,000 people dying from COVID in Brazil, and it’s going to get worse and worse. And the Brazilian budget for science, it was brought down to 25% this year of what it was 10 years ago. Currently, Brazilian science is in a very dire state. The students have no fellowships to continue working. Many people quitting science.
And the fact that we got this paper published in a good journal and that it got so much attention– I never got so much attention for anything I’ve published previously at all. And this, for me, it comes at a very good moment because I’m telling my students, don’t quit science. Stay in science. Science is important. Science is important for the world. And this moment in Brazil will be overcome. We will get out of this situation. We will have a government that believes in science and that invests in science and education.
I must say to do science, to perform and to continue doing science in Brazil, given the current situation, political and economic, is actually a political statement.
IRA FLATOW: Well, I hope that our interview and your work and us talking about it helps you out in your work and all the science work that could be going on in Brazil.
SIDARTA RIBEIRO: Thank you very much, Ira. Thank you for the opportunity.
IRA FLATOW: Sidarta Ribeiro, professor of neuroscience and the vice director and founder of the Brain Institute at the Federal University of Rio Grande do Norte in Natal, Brazil.