Do animals dream consciously?

A dog moves its paws, whimpers softly and tenses its muscles, as if it were chasing something in its sleep. A cat twitches its whiskers while its eyes move beneath closed eyelids. Such behaviours resemble human dreams, but they are not direct proof of them. An animal cannot tell us after waking up what it saw. Scientists therefore study sleep by measuring brain activity, eye movements, muscle tension and the way traces of earlier experiences are reactivated during sleep. Many mammals and birds go through REM sleep, which in humans is associated with frequent and vivid dreams. However, it is important to remember that the presence of REM sleep does not automatically mean that an animal is experiencing a dream with specific content.

Some of the strongest indirect evidence comes from experiments on rats. When a rat moves along a route, certain neurons in the hippocampus become active in a sequence corresponding to the places the animal visits. When the rat later rests or sleeps, similar patterns of activity appear again, often in an accelerated form. This phenomenon is known as neuronal replay. Studies show that during sleep, the brain reactivates information related to recently travelled routes, rewards and decisions that were made. This may help consolidate memory and support learning. However, it does not prove that the rat is seeing an exact “replay” of running through a maze in its dream. Brain activity can be measured, but its subjective content cannot be directly read.

REM-like states are not limited to mammals. Birds have sleep phases that show many similarities to mammalian sleep, even though their evolutionary lineages diverged hundreds of millions of years ago. In 2022, researchers also described regular periods of retinal movements, leg twitching and stillness in jumping spiders — small spiders whose behaviour resembled that observed during REM sleep. It was a fascinating discovery, but the authors did not claim that spiders definitely dream. They only demonstrated the presence of a physiological state similar to REM sleep. Similar behaviour alone does not tell us whether an animal experiences images, emotions or a conscious story.

Even more difficult is the question of conscious dreaming, also known as lucid dreaming. In humans, this means a situation in which the dreaming person becomes aware that they are dreaming and may sometimes be able to influence the course of the dream. In experiments, people in REM sleep confirmed by physiological measurements were able to respond to researchers using previously agreed eye movements or muscle contractions. This allowed them to communicate, while still asleep, that they understood a question and were carrying out a task. So far, no equally reliable method has been developed for any animal to confirm that it recognises its own state of being asleep and dreaming.

The most accurate answer, therefore, is this: many animals probably experiencesome form of dreaming because their brains reactivate previous experiences during sleep and enter states similar to those in which humans dream. However, we have no evidence that an animal knows while dreaming: “What I am seeing right now is not reality.” Conscious dreaming requires recognising one’s own mental state, and at present we cannot investigate this reliably without being able to receive an answer from the dreamer. Perhaps animals dream about hunting, playing or finding their way home. Science can now observe the sleeping brain — but it still cannot enter the world that brain creates.