Three kinds of evidence to suggest they do!
Everything that makes us what we are, from the structure of our limbs down to the arrangement of our cells has been selected to give us an advantage over thousands of years of evolution. So, by this logic, dreams must increase our chances of survival in some way. The nocturnal movies we experience every night can be funny, terrifying, at times enlightening, at times just plain nonsensical. Yet they do appear to serve a purpose beyond mere entertainment, terror, or confusion. Dream researchers are uncovering their crucial role in memory consolidation, fear extinction, and emotional regulation. Yet this begs the question, where in the branches of the evolutionary tree does dreaming start?
If you have a pet, I’m sure you’ve seen them shifting their paws and growling while asleep, as if chasing a squirrel in their dreams. Believing a dog – or any mammal for that matter – can dream does seem plausible. But what about birds? Or octopuses? The great dilemma of animal dreaming lies in the fact that they are unable to communicate verbally to actually tell us about their dreams. But does this mean that the study of animal dreaming is truly inaccessible to science?
A recent article (Malinowski, Scheel, and McCloskey, 2021) explores this very concept. The authors propose three different non-verbal lenses through which we could study animal dreaming, including dream-enacting behaviours, neural correlates of dreaming, and replay of newly acquired memories. Let’s dive in!
Dream Behaviours
Dream-enacting behaviours describe the sleeper physically re-enacting a dream behaviour. When we sleep, our bodies are in a state of paralysis. Our partners should be grateful for this as it keeps us from thrashing them as we fight a dreamed enemy! While we don’t enact the bigger movements in our dreams, our bodies do have detectable physiological responses that directly correlate to dream content. For example, LaBerge (1986) found that smooth eye movements during sleep correlate with visually tracking something in a dream, and that dreamed-of sexual activity can lead to orgasms! In essence, our bodies respond to our dream content.
Individuals who report themselves as “non-dreamers” have been observed exhibiting dream-enacting behaviour, indicating that they do dream, but without recall. They classify themselves as non-dreamers because they cannot make verbal reports of dreaming, yet behavioural evidence indicates they do, in fact, dream. The inability to describe a dreaming experience, therefore, cannot be sufficient evidence that an individual does not dream. By this logic, we cannot classify animals as “non-dreamers” simply because they cannot tell us of their dreams.
In 1979 Michel Jouvet conducted a series of experiments on cats in which he “turned off” the part of the cat’s brain responsible for sleep paralysis. He observed that during REM sleep, the cats would begin to display dream-enacting behaviours. They would move as if stalking prey, play or begin to groom themselves. Their eyes remain closed and they did not respond to any visual stimulus, their movements appeared to be entirely oneiric. The movements would stop when the cats returned to slow-wave (or non-REM) sleep. Medeiros and colleagues (2021) have also observed octopuses exhibiting dream-enacting behaviours. They found that during sleep, octopuses would vary ventilation rates, move their arms and change their body patterns in ways unrelated to their surrounding environments. If you’ve seen My Octopus Teacher, you would not find it hard to believe octopuses have sufficient consciousness to experience dreaming.
Neural correlates denote dreaming
Tracking neural correlates of dreaming is another non-verbal way through which we could detect animal dreaming. When we dream, there is heightened activity in certain areas of the brain. Using this, we can detect when someone is dreaming. However, the study of neural correlates of dreaming goes beyond simply knowing someone is experiencing a dream, it can give us an idea of dream content. Activation of different areas of the brain coincides with dream content. For example, Siclari and colleagues (2017) found that a different area will be activated for facial recognition than for walking or running in a dream. These findings could have the potential for us to not only study animal dreaming but to determine the contents of animal dreams. However, the technology is not quite there yet, but I look forward to seeing future developments of this technology.
Evidence of new learning
One of the main functions of dreaming is the consolidation of newly acquired memories. A specific neural pattern will fire when forming a new memory, then will replay during sleep. This has not only been shown in humans but in rats as well. Dupret and colleagues (2010) placed rats into a new environment and measured the “place-related firing” of neurons. While the rats were asleep, they observed similar neuron firing. Rats that had this neural replay process disrupted had impaired memory of the environment, indicating that neural replay is essential in forming new memories.
However, dreams are rarely exact replays of memories our brains are consolidating. The memories get warped and woven into other dream content, so in observing replays we would not expect to see the exact neural pattern repeated, but a slightly altered one. Gupta and colleagues (2010) discovered this changing neural pattern in rats. They found that the neural pattern played not just forwards, but backwards as well. They also observed the pattern changing in novel ways, indicating active learning.
Though animals may not be able to discuss their dream lives with us, there are many promising ways to study animal dreaming. As we unravel the evolutionary drivers behind dreams, we may continue to discover different avenues for the non-verbal study of dreams. Given all the evidence just discussed, I am inclined to believe that when my pup’s busy paws mimic running in her sleep, she truly is chasing her dream squirrel, and maybe even catching it for once.
References
Gupta, A. S., Meer, M. A., Touretzky, D. S., & Redish, A. D. (2010). Hippocampal Replay Is Not a Simple Function of Experience. Neuron, 65(5), 695-705. doi:10.1016/j.neuron.2010.01.034
Jouvet, M. (1979). What does a cat dream about? Trends in Neurosciences, 2, 280-282. doi:10.1016/0166-2236(79)90110-3
LaBerge, S., Greenleaf, W., & Kedzierski, B. (1983). Physiological responses to dreamed sexual activity during lucid REM sleep. Psychophysiology, 20, 454-455.
Laberge, S. (1986). Lucid dreaming: Psychophysiological studies of consciousness during REM sleep. Sleep and Cognition., 109-126. doi:10.1037/10499-008
Malinowski, J., Scheel, D., & Mccloskey, M. (2021). Do animals dream? Consciousness and Cognition, 95. doi:10.1016/j.concog.2021.103214
Medeiros, S. L., Paiva, M. M., Lopes, P. H., Blanco, W., Lima, F. D., Oliveira, J. B., . . . Ribeiro, S. (2021). Cyclic alternation of quiet and active sleep states in the octopus. IScience, 24(4), 102223. doi:10.1016/j.isci.2021.102223
Medeiros, S. L., Paiva, M. M., Lopes, P. H., Blanco, W., Lima, F. D., Oliveira, J. B., . . . Ribeiro, S. (2021). Cyclic alternation of quiet and active sleep states in the octopus. IScience, 24(4), 102223. doi:10.1016/j.isci.2021.102223
Siclari, F., Baird, B., Perogamvros, L., Bernardi, G., Larocque, J. J., Riedner, B., . . . Tononi, G. (2017). The neural correlates of dreaming. Nature Neuroscience, 20(6), 872-878. doi:10.1038/nn.4545