The observation of animal sleep patterns has long been of interest, dating as far back as 44 B.C.E., when the Roman natural philosopher Lucretius described “the twitching movements of dogs sleeping upon the hearth” (Hobson, p. 151—see Sources). However, it was during the 1950s that research into the sleep patterns of animals really peaked: first with the discovery by William Dement, that cats exhibit the phase of sleep called rapid eye movement (REM), followed by the experiments of two Frenchmen, neurosurgeon Michel Jouvet and his co-worker, the neurologist Francois Michel. Jouvet and Michel observed that a sleeping cat, devoid of motor output or movement, still exhibits an activated EEG, which means that while an animal is asleep, its mind is awake. Jouvet’s discovery led to the general understanding that during REM sleep “the body’s muscles are actively inhibited.” In essence, “we would act out our dreams were it not for this inhibitory suppression of motor out- put” (Hobson, p. 150—see Sources). Further, because it has been found humans experience the most active dreaming during REM sleep, this research may indicate that animals do dream, although it is, of course, impossible to say for sure because of the communication barrier.

Animals such as cats and dogs apparently have dreams, too, just like people; animals are also a theme in many people’s dreams.

It has been suggested that when animals dream, they are focused on the types of things they usually do in their waking state. For example, animals that use their noses a lot, such as dogs, have dreams with a significant olfactory component.

There was one behavioral study that showed that monkeys have visual dreams. Some monkeys were taught to respond to visual stimuli by pressing a button. Later, when they were sleeping, they made hand motions as if they were pressing buttons, suggesting that they were seeing some- thing. To add further credence, in a separate study, a gorilla who had been taught sign language put together two signs to form the combined term sleep pictures, presumably a reference to the visual components of dreams.

Again, in an experiment on cats, portions of the brainstem responsible for muscle inhibition during REM sleep were damaged. These cats entered REM sleep, and rather than lying quietly with their eyes moving, they stood up, walked around, and chased imaginary creatures, as if they were acting out their dreams without waking up.

Such findings, as well as our everyday observations of household pets that growl and make movements in their sleep, make it almost certain that animals dream in much the same way that we dream. The implications of this conclusion, however, tend to undermine certain dream theories, such as Sigmund Freud’s notion that the sole purpose of dreams is to allow us to act out socially unacceptable urges—an idea clearly inapplicable to animals.