Beyond our wildest wildlife dreams…

When your head hits the pillow at night, it’s like you’ve entered a different world. Even if you don’t remember it the next morning, you might have been moonwalking or time-traveling in your dreams the night before. Humans used to think this dream world was just for us – something that sets us apart from the rest of our animal friends. But what if lots of animals share our dream world? And what if, for some of them, you could see their dreams painted right on their skin? Don’t worry – it’s not like other people can see the wild adventures happening in your dreams (yet… [1,2].) But scientists might be able to tell what kind of dream our eight-legged friend the octopus is having just from looking at their color-changing skin. Sounds crazy, right? 

Here’s what we already know: human sleep happens in 2 main phases. Rapid eye movement (REM) sleep is when your brain is experiencing rapid activity, almost like how active it is when you’re awake. But, your body is kept paralyzed despite all this activity going on in your brain [3, 4].  Non-REM sleep is associated with slower brain waves and a lower heart rate. We think that most dreaming occurs during those more active REM cycles (though we also have evidence of non-REM dreaming… [5].) Our sleep goes back and forth between these two phases – sounds like a busy night! 

In the last almost 75 years since scientists first described REM, we have become more and more sure that other animals experience something like REM and non-REM sleep – mammals, birds, reptiles, you name it [3]! The big question was, and still is, why does this happen? Why don’t we just “shut off” when we sleep, but actually experience intense brain activity? While we don’t quite know those answers yet, studying sleep and dreams in other animals can tell us more about how our different and complex brains evolved. Based on which brain regions light up with activity while we dream, we think that dreaming could play a role in emotional memory processing [4,6]. So, when you see your dog running in his sleep, maybe he’s dreaming about the excitement of squirrel-chasing that day! 

Fido aside, scientists have recently become very interested in studying dreaming in octopuses. Even though they are invertebrates, so their brains evolved completely separately from us bony people, they also have something like active (REM) and quiet (non-REM) sleep states [7]. On top of that, they have amazing skin that can flash in different colors and patterns when they’re awake, helping them camouflage with their surroundings and even communicate with other octopuses and predators [7].  During the octopuses’ active sleep phase, scientists can often observe similar skin-changing flashes [7]. There was even a recent report about an octopus named Costello whose skin flashed like he was meeting a predator while he was asleep[8]! Could their color-changing skin mean that they’re having dreams (and nightmares) about their waking days, just like us? 

We’ll never really know for sure, at least not for a while – we can’t exactly ask octopuses to keep a dream journal for us! Maybe they’re just dozing, or maybe they truly are counting underwater sheep. The mysteries of the dream world still lie beyond our wildest dreams…

Image by @dustinhumes_photography courtesy of Unsplash

References

1. Horikawa, T. et al. (2013) Neural decoding of visual imagery during sleep. Science 340, 639–642

2. Xia, W. et al. (2023) DREAM: Visual decoding from reversing human visual systemarXiv [cs.CV]

3. Blumberg, M.S. et al. (2020) What is REM sleep? Curr. Biol. 30, R38–R49

4. Maquet, P. et al. (1996) Functional neuroanatomy of human rapid-eye-movement sleep and dreaming. Nature 383, 163–166

5. Siclari, F. et al. (2017) The neural correlates of dreaming. Nat. Neurosci. 20, 872–878

6. Zhang, J. et al. (2024) Evidence of an active role of dreaming in emotional memory processing shows that we dream to forget. Sci. Rep. 14, 8722

7. Pophale, A. et al. (2023) Wake-like skin patterning and neural activity during octopus sleep. Nature 619, 129–134

8. Ramos, E.A. et al. (2023) Abnormal behavioral episodes associated with sleep and quiescence in Octopus insularis: Possible nightmares in a cephalopod?bioRxiv, 2023.05.11.540348

Edited by Emma Hays