Animals also dream – here’s what we know

If you have ever watched a dog nap, you’ve probably wondered if animal dream.

It’s a complicated question. We still don’t know exactly why humans dream, or why dreams can be important. Studying animal dreams are even more difficult; dogs can’t tell us what made them whine or run during a nap.

Depending on how you define them, animal dreams could have intriguing implications.

“I think dreaming gives us a way to extend a number of cognitive abilities to animals; this includes things like emotion, memory and even imagination,” says David M. Pena-Guzmanwho studies philosophy of science at San Francisco State University and recently wrote When Animals Dream: The Hidden World of Animal Consciousness.

We know that primates have emotions, but think of spiders, which a recent study suggests may experience REM-like sleep and even visual dreams. The thought of spider dreams sounds weird, but it may be true.

“We have this idea that dreams are a confabulatory narrative with some kind of crazy, vivid elements,” says Matthew Wilson, a neurobiologist at MIT. “But when we look at animal models, we’re just trying to understand what’s going on during sleep that might influence learning, memory, and behavior.”

What do cats dream about

domestic cats were among the first animals subjected to dream research. Michel Jouvet, a pioneer in sleep studies, discovered feline dream proof in the 1960s, when he observed the behavior of cats while they slept and then changed it dramatically.

In REM sleep, human muscles don’t move much despite the intense mental activity that fuels our dreams. This state of atony ensures that the body does not fulfill our dreams, however real they may be. Jouvet learned that, in cats, a structure in the brainstem called pons seemed to regulate REM sleep and produce partial paralysis.

By removing parts of the pons, however, Jouvet caused a radical change in behavior. With their brains deep in REM sleep, the cats began to move as if awake, chasing, jumping, grooming and aggressively defending themselves against unseen threats.

Jouvet called this period paradoxical sleep, when the body is still but the mind remains fully active. This provided a window in what was going on in the sleeping brains of cats.

“The cats adopted behaviors that were very easy to interpret as a mapping of a waking experience,” says Peña-Guzmán.

Rats recall memories of the maze

Once rats have traversed a maze during the day, they can repeat the same course while they sleep, according to research. When awake, a rat’s hippocampus, a part of the brain responsible for creating and storing memories, remembers the neural blueprint for navigating the maze. Later, when sleeping, the brain reproduces the identical pattern, suggesting that the rat remembers or relearns the maze again.

This discovery of 2001 was one of the first to suggest that animals had complex dreams. And that was just the beginning, says co-author Wilson, the MIT neurobiologist.

“We’ve done other studies that suggest the way memories of past experiences wake up during sleep might be similar to what we would experience as dreams.”

These rat brain studies show that when maze memories occur during sleep, the visual imagery that accompanied them is also reactivated, meaning that sleeping rodents saw what they had seen in the maze when they were awake. The same was seen for auditory and even emotional areas that reactivate when the rat runs through the maze again during REM sleep. (Learn why rats avoid hurting other rats.)

“A lot of evidence suggests there is an extensive re-experience of the waking state during sleep,” Wilson says. “If we want to call it dreams, I’m perfectly comfortable with that description. The interesting part is, if that’s what’s happening, what does it mean? »

Zebra finches remember songs

Although known for their lyrical songs, zebra finches are not born singers. Birds need to learn by listening, doing and, perhaps, dreaming.

In 2000, researchers learned that neurons in the forebrain of birds fire in a distinct pattern when they sing a song, a song that scientists can recreate note by note. While birds sleep, their brains repeat this same pattern, replicating the song they heard and sang that day, suggesting that birds remember and practice songs while they sleep.

The study authors suspect songbirds dream of singing. Do dreaming birds relive their waking experiences? Or is singing dreams more like algorithms operating without consciousness? Scientists may be getting closer to the discovery.

After two decades of new research, finches were the first non-mammals found in have a sleep pattern similar to humans, including REM sleep. More recent work shows that birds also move their vocal muscles to match the music in their brain and can be tricked into singing a song that is played to them while they sleep.

Sleeping finches also produce variations on their songs, suggesting that they gather sensory information while awake and create adaptive changes by improvising new versions to support learning in a dream state.

Sleep soundly with fish

Zebrafish also experience REM-like sleepaccording to Stanford neurobiologist Philippe Mourain. While sleeping, these fish lose muscle tone, develop arrhythmic heartbeats, and show brain activity that resembles that of an awake fish. A noticeable difference from humans, but not all other animals, was that fish did not move their eyes. (Having no eyelids, they did not close them either.)

The finding suggests that REM sleep, the state in which most dreams occur, may have evolved at least 450 million years ago, before land and water animals diverged in their evolution.

“Twenty years ago, people told me that fish don’t even sleep,” says Mourrain. “Now we see… these behavioral characteristics are carried over from insects to spiders and vertebrates. And during REM sleep, you lose control of your most vital regulatory systems. Evolution wouldn’t have maintained such a fragile state if it didn’t matter.

But why is dreaming important? Does the conservation of REM sleep through evolution mean that even fish could dream?

It depends on your definition of a dream. For Mourrain, dreaming is simply explained as a mere shuffling of synapses, or in other words, a resetting of neural connections that prepare our nervous system for the day ahead through processes such as memory consolidation and optimization of cognition.

“I wouldn’t be surprised if real dreams were found in animals, and I think we can eventually prove it scientifically,” he says.

“You did something during the day, and your brain will replay it, integrate it, and mix it with other experiences. We’re not the only species capable of remembering and learning.