Recently I dreamed of a giant squid with a huge eye made of a thousand tiny fish. If one fish swam away, the squid had a blank spot in its vision until another fish replaced it.

What could it mean? Teamwork? Life’s interconnectedness? Or just the typical dreams of a weird-animal writer? (See "Why Do We Dream? To Ease Painful Memories, Study Hints.")

Whatever the reason, it fits well with Saturday’s Weird Animal Question of the Week, which Unni Krishnan asked us on Facebook: “Do animals dream?”

While They Were Sleeping

It’s uncertain whether animals dream, but “it seems very likely,” Hugo Spiers, an experimental psychologist at University College London, says via email. (Find out whether big animals always sleep standing up.)

The Funny Ways That Animals Sleep WATCH: Floating walruses, twitching puppies, upside-down bats—see the unusual (and funny) ways that animals sleep.



Spiers and colleagues have found that when lab rats are shown food and then go to sleep, certain cells in their brains seemed to map out how to get to the food, according to a study published in June in the journal eLife.

You might say they "dreamed" their path to a reward.

In people, dreaming occurs during rapid-eye movement, or REM sleep, which most mammals also experience.

So "it is reasonable to suppose that animals have something like what we call dreams," says Patrick McNamara, director of the Evolutionary Neurobehavior Laboratory at Boston University.

The sleeping cats raised their heads, suggesting they were watching unseen objects; arched their backs; and appeared to stalk prey and get in fights.

View Images Cats likely see images during deep sleep, though they may not be dreams as we know them. Photograph by Masataka Komori, Aflo/Corbis

All of these behaviors suggest cats were seeing images during REM, McNamara says, though we can’t say for sure if they were dreaming like we do. (Watch a mother cat hugging a kitten having a "bad dream.")

In another eye-opening sleep study published in 2001 in the journal Neuron, scientists compared the brain patterns of rats running through a maze with their brain patterns during REM sleep afterward. (Find out how bees get their Zzzs.)

The scientists, Michael Wilson and Kenway Louie of MIT, found the brain patterns were so similar they could tell what part of the maze the rats were "dreaming" of.

The study fits with the idea that physical spaces, like the maze, "are encoded into long-term memory during REM sleep,” McNamara says.

Dream a Little Dream of Me

My squid dream got me curious: Can cephalopods—a group that includes squid, octopuses, and cuttlefish—dream?

“It’s possible, it all depends on your definition of 'dreaming,'” Spiers says. (Read about the mysteries of why we sleep in National Geographic magazine.)

For instance, cuttlefish exhibit a sleep-like state accompanied by color changes, twitching, and rapid eye movements similar to REM sleep, according to a 2012 study in the journal PLoS ONE .

Who knows, maybe that giant squid is out there in the ocean dreaming about me.