What do animals dream while they sleep?

If you’ve ever watched a dog take a nap, you’ve probably wondered if animals can dream.

It’s a complicated question. We still don’t know exactly why we dream, or how those dreams can have any significance. Animal dreams are even more difficult to study: dogs are completely unable to tell us what makes them growl or run in their sleep.

Depending on how we choose to define them, animal dreams can have interesting interpretations.

“I think dreams give us reason to apply a number of cognitive abilities to animals, such as emotions, memory, and even imagination,” says David M. When Animals Dream: The Hidden World of Animal Consciousness.

We know primates have emotions, but take spiders for example: According to a recent study, spiders experience periods of rapid retinal movements, similar to human rapid eye movement (REM) and may experience visual dreams. It may seem strange to imagine spiders dreaming, but it seems they are.

(Read: Do spiders dream in their sleep?)

“We see dreams as fantastical stories with crazy elements, which can seem real,” says Matthew Wilson, a neuroscientist at MIT. “But when we look at animals, we’re just trying to understand what’s going on during sleep that might influence learning, memory and behaviour.”

Cat dreams

Domestic cats are among the first animals to be subjected to dream research. A pioneer in the study of sleep, Michel Jovet discovered evidence of dreaming in felines in the 1960s by observing and then significantly modifying the behavior of cats while they slept.

In humans, during rapid eye movement, or rapid eye movement, the muscles don’t move much despite the intense mental activity that fuels our dreams. This state of harmony ensures that the body does not interpret our dreams, even if they seem real. Jovet found that in cats, a structure in the brainstem called the pons appears to regulate REM sleep and produce partial paralysis.

(Read: This is what your dreams look like.)

By removing parts of the bridge, the scientist caused a significant change in behavior. While their brains were in REM sleep, the cats began moving as if they were awake, chasing, jumping, grooming, and even violently defending themselves against unseen threats.

Jovet called this period paradoxical sleep: the body is immobile, but the mind remains fully active. This experiment provided a better understanding of what was happening in the cats’ brains while they slept.

“You can easily interpret these cats’ behavior as versions of the experiences they had when they were awake,” says Peña Guzmán.

Laboratory run mice

A study showed that after walking through a maze during the day, rats are able to repeat the same cycle while sleeping. When the mouse is awake, the hippocampus, the part of the brain responsible for forming and storing memories, memorizes the neural pattern needed to navigate through the maze. Later, during sleep, its brain repeats the same pattern, indicating that the rat is remembering or learning the path of the maze.

This discovery, made in 2001, was one of the first to suggest that animals could have complex dreams; And according to Wilson, this was just the beginning.

We have conducted other studies that suggest that replaying memories of past experiences during sleep may be similar to what we experience as dreams. »

These rat brain studies show that when these memories of the maze came back while they were asleep, the accompanying images returned too, meaning that the rodents saw in their sleep what they saw in the maze when they were awake. The same phenomenon has been observed in the auditory and affective regions of the brain that are activated when the rat reproduces the course of the maze during REM sleep.

“There is a lot of evidence that deep wakefulness occurs during sleep,” says Wilson. “I am quite comfortable with the idea of ​​calling this phenomenon ‘dreaming.’ But if this is what is happening, what does that mean? That is what is interesting.”

(Read: How do animals sleep?)

Dreams of Diamond Mandarin Songs

Although they are best known for their singing songs, zebra finches are not a born singer. These little birds learn by listening, practicing, and maybe even dreaming.

In 2000, researchers discovered that when they sing, neurons in the forebrain of zebra finches fire in an exact pattern that scientists can recreate note by note. When they sleep, their brain reproduces this same pattern; Thus they reproduce the song they heard and practiced that day, indicating that they remember it and rehearse it in their sleep.

According to the study’s authors, songbirds also sing in their dreams. Do they relive their daily experiences in their dreams? Or are these dreams more like algorithms operating in the bird’s subconscious? Scientists may be about to find out.

After more than twenty years of research, zebra finches were the first non-mammal animals to exhibit a sleep pattern similar to that of humans, including REM sleep. More recent work has shown that birds also move their vocal muscles in response to music in their brains, and can even be tricked into singing aloud to them while they sleep.

When they sleep, zebra finches also compose variations of their songs: they collect sensory information during the waking period, and they produce adaptive changes by improvising new versions to support their learning in their dreams.

Do fish dream like humans?

According to Philip Morean, a neuroscientist at Stanford University, zebrafish also experience REM sleep. When they sleep, these fish’s muscle tone decreases, their heartbeat becomes irregular, but their brain activity remains similar to that of an awake fish. A noticeable difference between fish and humans is that fish do not move their eyes while sleeping; And in the absence of eyelids, she does not close them either.

This finding suggests that REM sleep, the state in which most dreams occur, may have evolved at least 450 million years ago: before evolution triggered terrestrial aquatic animals.

“Twenty years ago, I was told that fish don’t sleep,” Morin says. Now we note that these behavioral characteristics are found everywhere, from insects to spiders and vertebrates. And during REM sleep, we lose control of our most vital regulatory systems. Evolution would not have maintained such a fragile state if it had not been for some importance. »

But why are dreams important? If Evolution Preserved REM Sleep, Can Fish Dream?

(Read: Our Dreams, Windows into Our Fears.)

It all depends on what definition we have of a dream. For Maureen, the dream is about rewiring synapses or, in other words, resetting the neural connections that prepare our nervous system for the day ahead through processes such as strengthening and improving memory and cognition.

“I wouldn’t be surprised to find out that animals dream like us, and I think one day we’ll be able to prove it scientifically,” says the neuroscientist.

“We do something during the day, and our brain takes it back, integrates it, mixes it with other experiences while we sleep. We are not the only species capable of remembering and learning.”

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