Animals Dream Too—here's What We Know

If you've ever seen a dog sleeping, you've probably wondered if you dreamed about animals.

This is a difficult question. We don't really know why people dream and why dreams are important. Studying the dreams of animals is more difficult; Dogs can't tell us what makes them cry or run in their sleep.

However you interpret it, dreaming about animals can have interesting implications. ( More on Sleep Secrets.)

I think dreams allow us to extend different cognitive abilities to animals; This includes things like emotion, memory, and imagination,” says David M. Pena-Guzman : “The Hidden World of Animal Consciousness .”

We know primates have feelings, but consider spiders, according to a recent study they can experience REM sleep and even dream. The idea of spider dreams sounds funny, but it can be true.

"We have crazy things like dreams as complex narratives," says Matthew Wilson, a neuroscientist at the Massachusetts Institute of Technology. "However, when we study animal models, we try to understand what happens during sleep, which can affect learning, memory and behavior."

Why do cats dream?

Domestic cats were among the first animals used for dream research. Michel Jewett, a pioneer in sleep research, discovered evidence of cat dreams in the 1960s when he observed and then dramatically altered the behavior of cats while they slept.

During REM sleep, despite the intense mental activity that fuels our dreams, a person's muscles rarely move. This state of atony causes our body not to realize our dreams, even if they seem true. Jewett learned that in cats, a structure in the brainstem called pons controls REM sleep and causes partial paralysis. (Read how scientists are trying to make our dreams come true.)

However, by removing parts of the bridge, Juvet made dramatic changes to the character. As their brains entered deep REM sleep, the cats began to behave as if they were awake, chasing, jumping, grooming and aggressively defending themselves against unseen threats.

Jouvet called this period REM sleep, where the mind stays fully awake while the body stays still. It opened a window into what goes on in the minds of sleeping cats.

"The cats exhibited behaviors that could easily be interpreted as reflecting their waking experiences," Pena Guzman said.

The mice remember the maze

Studies have shown that rats can repeat the same thing during sleep after having a seizure during the day. When awake, the hippocampus of rats, the part of the brain responsible for creating and storing memories, remembers the pattern of neural navigation through a maze. Later, during sleep, the brain repeats the same pattern, indicating that the mouse remembers or learns repeatedly.

This is the year 2001 discovery was one of the first to suggest that animals have complex dreams. It was just the beginning, said co-author Wilson, a neuroscientist at the Massachusetts Institute of Technology.

"We've done other research that suggests memories of past experiences that emerge in dreams may be similar to what we hear in dreams."

These rat brain studies revealed that when maze memories occurred during sleep, the accompanying visual images were restored, meaning that the sleeping rats saw what they had seen while asleep. The same auditory and even emotional areas were found, which were recorded when the mouse played in the maze during REM sleep. (Learn why mice don't hurt other mice.)

"There's a lot to suggest there's a recycling of the wakeful state during sleep," says Wilson. "If we want to call them dreams, I'm very happy with that statement. What does it mean when the most surprising thing happens?"

Zebras remember songs

Although zebra finches are known for their lyrical songs, they are not natural singers. Birds need to learn by listening, doing, and maybe even dreaming.

In the year 2000, researchers discovered that neurons in the forebrain of birds fire in an orderly fashion when they sing a song that scientists can reconstruct from memory. As the birds sleep, their brain repeats the same pattern, recalling what they heard that day and the song they sang, prompting the birds to remember and practice the songs while they sleep.

The authors of the study doubt that songbirds dream of singing. Do sleeping birds relive their waking experiences? Or do we sing dreams like algorithms operating unconsciously? Scientists may be getting closer to the solution.

After more than two decades of research, finches have become the first non-mammals to have sleep patterns similar to humans, including REM sleep. Recent studies have shown that birds move their vocal muscles to match the music in their brains and can make them sing while they sleep.

Hibernating finches produce variations of their songs, prompting them to gather sensory information while awake, and to make dynamic changes, evolving new versions to facilitate learning in a sleep-like state.

Deep sleep with fish

According to Stanford neuroscientist Philip Murren, zebrafish also experience REM sleep. During sleep, these fish reduce muscle tone, irregularly increase heart rate, and exhibit brain activity similar to that of active fish. A significant difference from humans, if not all other animals, is that fish do not move their eyes. (And, without lashes, they don't close.)

The findings suggest 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," Murren says. "Now we see...these behavioral traits are retained in everything from insects to spiders to vertebrates. And during REM sleep, you lose control of your most important control systems. If evolution hadn't happened, she wouldn't have maintained such a delicate state."

But why is sleep important? Does the evolution of REM sleep mean that even fish can dream? (Read how sleep is quickly becoming a "night cure" for people.)

It depends on the definition of your dream. For Moran, dreams are simply explained by the exchange of synapses, or in other words, the adjustment of neural connections that prepare our nervous system for the next day through processes such as memory consolidation and cognitive facilitation.

"I wouldn't be surprised if real dreams were found in animals, and I think we can scientifically prove it in time," he said.

"You do something during the day and your brain replays it, integrates it, and integrates it with other events. We're not the only ones with the ability to remember and learn."