(CNN) — June appears to be dreaming of a chase. As soon as this long-haired German Shepherd lays down for a nap, her limp limbs often start moving and kicking. To her owners, she appears to be on the trail of unseen prey.
“When he’s sleeping, sometimes his legs move aggressively, frantically, like he’s running on an invisible treadmill,” says his owner, Wudan Yan, who lives in Seattle.
“You’re dreaming, right?” Yan asks. “She is dreaming of chasing squirrels and rabbits.”
The kinds of behaviors Yan has observed are common, said neuroscientist Mark Frank, a Washington State University professor who studies the role of sleep in animals. “I’ve seen it in my own dogs. They run, whine, bark and wake up like they don’t know where they are,” he explains.
What does June really dream about? What happens to animals while they sleep has piqued human curiosity for thousands of years, but clear answers have been elusive. “If a dog gave us a report, maybe we could answer the question,” says Frank.
Until then, we will have to make do with science. This is what we know.
What causes the shakes?
Involuntary muscle jerks, called myoclonus, are common in both dogs and humans. That’s what it looks like when a dog’s limbs and paws tremble or move repeatedly during sleep. It is more frequent during REM sleep. Eye blinking is also associated with the REM phase.
And in humans, REM sleep has historically been associated with vivid dreams. It’s the stage where you have those kinds of weird, colorful experiences that you can’t wait to tell your family over breakfast.
Dogs sleep a lot in the REM phase, which accounts for about 12% of their lives, according to a 1977 study published in the academic journal Physiology & Behavior. And since other aspects of sleep in dogs closely resemble our own, scientists think the parallels could extend to sleep.
“From dogs to humans, most mammals have the same basic sleep states,” says Frank. “We can’t conclusively say that dogs have experiences like ours when we dream, but it’s hard not to imagine that they do.”
When movement during sleep becomes more elaborate, more than just myoclonus may be occurring.
“Sprinting while sleeping is not that common,” says Frank. “There’s a mechanism in the brain that actively paralyzes you from the neck down. It’s a fascinating phenomenon, and it’s what normally prevents you from acting on your dreams.”
That structure, called Varolio’s bridge, is located in the brainstem. Damage to this structure can short-circuit its ability to paralyze the body while it sleeps.
Scientists discovered in the 1970s that if the brainstem of domestic cats was injured, the animals became much more active while they slept. In the study, the cats were observed to raise their heads, move their limbs and jump.
Damage to the pons from neurological disorders can also affect the brain’s ability to paralyze the body during sleep. For humans, a large increase in shaking during sleep can be an early warning sign of Parkinson’s disease, Frank said. If you see the same thing in your dog, he noted, it’s worth taking him to the vet.
What really happens and why?
In the case of humans, REM sleep is thought to play a role in memory consolidation. There is some evidence that it works the same way in animals.
In a 2001 study published in the academic journal Neuron, researchers who observed brain wave activity in sleeping rats concluded that the animals replayed the events of the day. When the rats walked through a circular maze before falling asleep, they seemed to repeat portions of their walk through the maze while they slept. And in 2017, a study, published in the journal Scientific Reports, found that dogs could use their nap times to reinforce established memories while awake.
The dogs that participated in the study began by learning to follow new voice commands. One week after the initial training, the animals that slept, rather than played, after the lesson were able to perform the associated task better than their counterparts in the control group. It is possible that they, too, were replaying the events of the day while they slept.
When dogs sleep, “there’s no reason not to believe that they’re not reliving some sort of earlier experience,” says Marc Bekoff, professor emeritus of ecology and evolutionary biology at the University of Colorado Boulder and author of “Canine Confidential: Why Dogs Do What They Do”.
This also applies to the wild cousins of dogs. Bekoff has spent countless hours conducting field research that includes observing wolves and coyotes in their sleep, and says they display the same behaviors that pet owners see in their canines while they sleep.
But even if dogs, wolves, and coyotes replay the day’s events when they’re asleep, the results can look (or smell) very different from human dreams. “We have exceptional vision, but dogs … that’s not their realm,” says Frank, the Washington state professor.
Although dogs do not have the best eyesight in the world, they have a phenomenal sense of smell.
“I think there is a sensory context that has to fit the mental content,” he says. “I’ve always wondered, when dogs dream, is it a world of smells they’re experiencing?”
Why are we so obsessed with our dogs’ sleep?
Today’s pet owners may be especially fascinated by the lives of their companions while they sleep, but interest in animal dreams dates back to ancient times, says philosopher David M. Peña-Guzmán, associate professor Humanities and Liberal Studies at San Francisco State University.
“There are references to animal dreams in the work of people like Aristotle and a couple of other Greek philosophers,” said Peña-Guzmán, who is also the author of the forthcoming book “When Animals Dream: The Hidden World of Animal Consciousness.” “.
Even then, humans liked to speculate on the dreams of animals they were bonded with, such as dogs and horses, he said. Spending a lot of time with a pet, Peña-Guzmán noted, makes it easier to imagine them as creatures with a rich inner life. Less cute species, such as frogs and insects, are often ignored in ancient accounts.
Why is a philosopher interested in the dreams of animals? In his book, Peña-Guzmán argues that the ability to dream suggests that an animal experiences consciousness. And when we acknowledge an animal’s conscience, he wrote, we are more likely to value its experiences, to believe that they deserve respectful treatment.
And Peña-Guzmán finds dreams throughout the animal kingdom. He described a sleeping octopus whose color turns kaleidoscopic, which some scientists consider evidence of REM sleep. He wrote about zebra finches whose brain activity during sleep looks the same as when they are singing a song. Peña-Guzmán believes that fish probably dream too.
Peña-Guzmán acknowledges that not all animalists agree with his conclusions about dreams, but one thing is clear: we have a lot to learn about animal sleep.
“In the dream you really see the power of the mind at work,” Peña-Guzmán says. “It’s a really powerful reminder of how much we’ve underestimated and studied animals and how much the animal mind is still such uncharted territory that we know relatively little about.”