Do Animals Dream?

Practically all mammals and birds studied show both non-REM sleep and a REM-like stage with an active brain and relaxed muscles. The amounts vary a great deal. Many young animals spend much of their sleep in the active state, and the platypus shows a remarkable amount of REM-type activity. Dolphins, which sleep with one brain hemisphere at a time, show little or no clear REM at all.

In recent years similar two-stage patterns have been reported far from mammals: in bearded dragons, in cuttlefish and octopuses whose skin flickers through color patterns during 'active sleep,' and even in jumping spiders whose legs twitch and eyes move during sleep-like rest. None of this proves those animals dream, but it suggests that a quiet phase and an active phase of sleep are very old. The REM sleep guide explains the human version.

The most persuasive clue comes from recording individual brain cells. In rats that ran a maze, researchers found that patterns of hippocampal activity from the run reappeared during later sleep, including REM, sometimes at a similar pace. The animals were, in a measurable sense, going over the route again. Other work shows similar replay of places and sequences during non-REM sleep, tied to memory consolidation.

Songbirds offer another window. In sleeping zebra finches, neurons in a song-control region fire in patterns resembling those produced while the bird sings, as if the song were being rehearsed silently. Replay is not the same as a vivid movie with a plot, but it is the closest thing science has to seeing the raw material of a dream in an animal's brain.

In the 1960s, the French researcher Michel Jouvet found that damaging a small brainstem region in cats removed the muscle paralysis of REM. Those cats would rise during REM, stalk, pounce, and hiss at nothing — behavior that looked very much like acting out a hunt or a fight. It remains one of the most striking hints that cats experience something scene-like in sleep.

Dogs cycle through non-REM and REM much as we do, only in shorter cycles. Hungarian researchers have recorded family dogs' sleep with non-invasive EEG and found that a dog's daytime experiences, including emotionally charged ones, change how it sleeps afterward. Twitching paws, soft barks, and rapid eye movements usually cluster in REM. It is a reasonable guess — though only a guess — that dogs dream about their ordinary lives: people, smells, play, and the occasional squirrel.

We cannot know what an animal feels in sleep, but some dogs whimper, growl, or wake suddenly looking confused, and animals with traumatic histories may sleep more restlessly. Stress, pain, and unfamiliar surroundings all disturb animal sleep in ways that look similar to humans with bad nights.

If your dog seems distressed, it is usually wiser to call its name softly from a short distance than to touch it. A dog startled out of deep sleep can snap before it knows where it is. Frequent violent movements, collapse, or episodes that look like seizures deserve a veterinarian, not a dream theory — some animals, like some people, have genuine sleep disorders.

If many animals replay experience during sleep, dreaming may be rooted in very old functions: consolidating memory, rehearsing movement, and practicing responses to threat. That fits the scientific theories described in why we dream, and it softens the idea that dreams are purely a human puzzle of symbols.

It also explains why animals are among the most common figures in human dreams. They carry instinct, loyalty, fear, and freedom in a form older than language. When a wolf, horse, or spider appears in your night, you are borrowing from the same deep stock of experience that other animals may be sorting through in their own sleep.