One study found that rats map out navigational routes to get food during rapid-eye movement (REM) sleep.
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?
One study found that rats map out navigational routes to get food during rapid-eye movement (REM) sleep. [Photograph by Chris Scuffins, Ocean/Corbis]
It’s uncertain whether animals dream, but “it seems very likely,” Hugo Spiers, an experimental psychologist at University College London, says via email.
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.
McNamara notes that in 1959, French neuroscientist Michel Jouvet and his team altered cat brains to disable the mechanism that inhibits movement during REM sleep.
The sleeping cats raised their heads, suggesting they were watching unseen objects; arched their backs; and appeared to stalk prey and get in fights.
Cats likely see images during deep sleep, though they may not be dreams as we know them.
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.
Cats likely see images during deep sleep, though they may not be dreams as we know them [Photograph by Masataka Komori, Aflo/Corbis]
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.
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.
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. 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.