Do animals dream? If you’ve ever had a cat or a dog you would probably answer ‘yes’ – it certainly seems like they are dreaming when they sleep, from the way they sometimes twitch or move in their sleep, like this kitty who appears to be dreaming of riding a bike!
But oneirology, the study of dreams, is more or less completely reliant on dream reports: written or verbal accounts of dreams. And as much as we’d love to talk to our pets and understand what they’re saying to us, we can’t. So it’s not like we can ask them if they were really dreaming. Those twitches or big limb movements could be simply just movements; there might not be any dream content that goes with them.
However, there are some reasons to believe that some animals may dream. In cats as well as in humans, there is a certain bit of the brain that keeps up mostly paralysed during rapid-eye-movement REM sleep called the pons. When we go into REM, this part of the brain keeps us still – we cannot move (see also sleep paralysis). In the 1970s, a researcher wanted to know what would happen if cats didn’t have a functioning pons (Jouvet, 1979). So he performed a procedure on some cats which lesioned (cut) their pons, and then watched to see what would happen when the cats next slept.
What he found was that the cats, during sleep, began to perform various behaviours you’d expect to see them doing whilst awake:
- Stalking, as if pursuing a prey
- Attacking behaviours
- Flight behaviours
- Arching back as if angry
- Grooming themselves
From this, it certainly looks like they’re acting out dreams! But how do we know that there was any mental content that goes with these movements? What if the movements are just movements, devoid of any dream content?
To try and understand this further, we can look at humans. Since ethical guidelines for humans are much stricter than they are for non-human animals, it’s not possible to repeat this experiment with humans. However, there is a disorder that humans can get that makes them lose the paralysis that normally accompanies REM sleep, called REM sleep Behaviour Disorder (or RBD). When RBD patients sleep, they too can sometimes be seen acting out their dreams. But unlike with cats, we can actually confirm with those humans that they were indeed dreaming of the behaviour they are enacting while asleep through their verbal report. For example, Isabella Arnulf, who treats RBD patients, reported that one patient dreamt “that he was a police duck flying after a pigeon thief. Meanwhile, his wife observed him squatting on the bed, waving his arms as if flying, and shouting the two-tone sound of a siren while also mimicking a duck’s voice” (Arnulf, 2019, p.247). Since the movements in these humans was a case of them acting our their dream content, perhaps we could extrapolate this to Jouvet’s cats and make the case that this is what they were doing, too.
There’s potential evidence of non-mammalian animals dreaming, too. For example, zebra finches have been shown to ‘replay’ their birdsong when they sleep, to consolidate the memory of the song (Dave & Margoliash, 2000). You may also remember a video that did the rounds which appeared to show an octopus dreaming.
Rats do this too, ‘replaying’ an waking experience of running around a maze when they sleep to consolidate the memory of how they navigated the maze (Ji & Wilson, 2007). What’s especially fascinating about this study is that the ‘replay’ was not just in the hippocampus (a brain structure important for memory) but also in the visual cortex (an area of the brain important for seeing); were they actually seeing the maze while they slept? If so, this would be a dream!
So do animals dream, or not? The honest answer right now is that we don’t know for sure because we can’t ask them; but, there’s fairly decent evidence that they might.
If you want to read an academic article discussing whether all mammals dream, take a look at Manger and Siegal (2020).
Arnulf, I. (2019). Dreaming in parasomnias. In K. Valli & R. J. Hoss (Eds.), Dreams: Understanding Biology, Psychology, and Culture, Vol. 1, pp. 238-249.
Dave, A. S., & Margoliash, D. (2000). Song replay during sleep and computational rules for sensorimotor vocal learning. Science, 290(5492), 812-816.
Ji, D., & Wilson, M. A. (2007). Coordinated memory replay in the visual cortex and hippocampus during sleep. Nature Neuroscience, 10(1), 100-107.
Jouvet, M. (1979). What does a cat dream about? Trends in Neurosciences, 2, 280-282.
Manger, P. R., & Siegal, J. M. (2020). Do all mammals dream? Journal of Comparative Neurology. Doi: 10.1002/cne.24860