Do animals dream? What science already knows

The short answer

Dream interpretation is not prediction and not diagnosis. This article separates what sleep research observes from what popular interpretation associates with the theme, always saying which is which.

Nobody can say for sure that animals dream the way we do, because you cannot ask a rat or a dog to tell you about its dream. But research has already found that many animals have sleep stages similar to ours and that, during sleep, the brains of some of them replay activity patterns from when they were awake. For many scientists, that is the closest anyone gets to observing a dream from the outside.

Dogs and cats also have REM sleep, the stage in which humans usually have their most vivid dreams, and it is common to see them move their paws, whiskers and eyes while they sleep. If your question is about what dreams do for us, start with why we dream.

Read also: Why pets seem to understand our emotions and Dreaming about dogs.

What can be measured when the animal cannot talk

With people, the path is simple: wake someone up during sleep and ask what they were dreaming. That is how William Dement and Edward Wolpert, in 1958, linked rapid eye movements to dream reports and found that outside stimuli, such as water sprayed on the skin, made their way into the plot. That work helped establish REM sleep as the stage of the most vivid dreams.

With animals, two clues remain. The first is brain activity: recording neurons while the animal does something awake and comparing that with what they do during sleep. The second is behavior: movements, sounds and expressions during sleep. Neither one shows the "content" of the dream, but together they say a lot.

Source: Dement and Wolpert, Journal of Experimental Psychology, 1958.

Rats that replay the day during REM sleep

Kenway Louie and Matthew Wilson simultaneously recorded the activity of several neurons in the hippocampus of rats, a region tied to memory, while the animals were awake and active, and then while they slept. During REM sleep, the same neurons fired again in sequences that reproduced patterns from the waking experience, lasting from tens of seconds to minutes, and on a time scale similar to the original.

The authors describe this as the reactivation of long sequences that suggest memory traces of lived episodes. They propose that this replay may be important for memory processing and that it opens the way to studying, with electrodes, the content of dream states. In other words: the rat seems to "go over" what it did, and it is tempting to call that a dream, although nobody can confirm what it experiences.

Curiously, it is humans who dream about the animal: there is an article on dreaming about rats for anyone who arrived here that way.

Source: Louie and Wilson, Temporally structured replay of awake hippocampal ensemble activity during REM sleep, Neuron, 2001.

See also: Dreaming about a shadow figure and Do we dream in color or in black and white?.

Birds that rehearse their song while asleep

Zebra finches learn to sing by matching what they produce with their voice to what they hear. Amish Dave and Daniel Margoliash studied neurons in a motor area of the brain of adult birds of this species. During sleep, when a recording of the bird's song was played, the activity of these neurons reproduced, with very precise timing and structure, the activity from when the bird sang during the day.

Even more interesting: even with no sound playing at all, the spontaneous activity of these neurons during sleep also matched that of the song. The authors called this a form of song "replay." Their proposal is that, outside the moment of singing, during sleep for example, the brain compares what was rehearsed with what it expects to hear, and uses that to fine-tune the song.

Source: Dave and Margoliash, Song replay during sleep, Science, 2000.

Dogs and cats: what you see on the couch

Anyone who lives with pets knows the scene: after a while of calm sleep, the dog starts moving its paws as if running, its eyes move under the lids, its tail gives a few little thumps and sometimes a soft whimper or a muffled bark comes out. Cats twitch their whiskers, ears and the tips of their paws. These episodes are usually short, and the animal goes back to being still soon afterward.

It is common to imagine that the dog is dreaming about its walk, another dog or its owner, and the findings in rats make that idea plausible. But there is no study showing what a dog or cat dreams about. The most honest thing to say is that they have the kind of sleep in which human dreams are most vivid and that they behave as if something were happening.

A practical rule: do not wake the animal with a fright or a sudden touch during these movements. It may wake up disoriented. If you need to, call its name calmly from a short distance.

When movement during sleep calls for a vet

Moving the paws, trembling slightly and making noises during sleep are usually part of normal sleep. A seizure is different, and a few differences help you recognize what is not a dream:

• the body becomes stiff, with the legs stretched out and rigid, or the movements are strong and rhythmic;
• there is heavy drooling, sometimes with foam, or the animal urinates or defecates without noticing;
• it does not wake up when called and, afterward, may be confused, unsteady or unable to recognize its surroundings for a while;
• the episode also happens while the animal is awake.

In these cases, see a veterinarian. If you can, record a short video of the episode and note how long it lasted: that helps a lot during the visit. An episode that does not stop within a few minutes, or several in a row, is a reason for emergency care. Only a veterinarian can assess what is going on.

What psychology and popular belief say

In psychology. Freud was direct: "I myself do not know what animals dream of." But he recalled a proverb a student had shown him, which asks what geese dream of and answers: of maize. For Freud, that answer summed up the idea that dreams fulfill wishes. Today science looks at animals along another path, that of memory, as with the rats and birds above.

In popular belief. Dream books talk about the opposite, humans who dream about animals. O Livro dos Sonhos, a Brazilian dream book by L. P. Baçan, reads the entry "animal" as insecurity in life and an uncertain passion in love; "dog" as new friendships; "cat" as good luck. For those readings, see dreaming about cats. And if the pet that appears in the dream has already passed away, there is a gentle article on dreaming about a pet that died. These are interpretations from tradition, not predictions. See what dream meanings look like according to science and culture.

Sources: Freud, Die Traumdeutung, 1900; L. P. Baçan, O Livro dos Sonhos, 2014.