By Matt Soniak
According to the National Sleep Foundation, dogs spend about half their day (or, more precisely, 12 to 14 hours of every 24-hour cycle) sleeping. Puppies, senior dogs and certain breeds get even more shuteye, around 18 to 20 hours. With all that sleep, it’s easy to wonder if dogs dream like people do. Find out more about what’s going on in your dog’s head while he’s dozing, below.
Do Dogs Dream?
For Matt Wilson, a neuroscientist who studies memory and learning at the Massachusetts Institute of Technology, there is no question that many animals dream. Dogs, and other animals, actually aren’t that different from us when it comes to certain aspects of sleep.
“When you look at brain structure, when you look at sleep physiology, the brain activity that goes on, the equivalence of the sleep states, it's all very comparable,” Wilson says, regarding the mammal family tree. Humans, dogs and all other mammals experience rapid eye movement (REM) sleep, the sleep stage during which we experience dreams. We all also have similarly high levels of brain activity during this stage of sleep, and have a brain structure called the Pons Varolii–which paralyzes our major muscles during REM sleep to keep us from moving around too much and “acting out” our dreams–in common.
Of course, we can’t talk to dogs and compare our dreams to theirs, so it might seem hard to say for sure if other animals dream like we do. But in 2001, Wilson did the next best thing to try and find out. He took a peek inside the brains of sleeping rats.
Wilson recorded the activity of the rats’ neurons, or brain cells, as they ran through a maze, and saw that the cells “fired” in a distinct pattern. When he looked at the neurons’ activity again while the rats were in REM sleep, he saw the exact same pattern of activity, happening at almost same speed as when the rats were awake. The rats’ brains were replaying their trip through the maze while they slept.
Wilson tried a similar experiment a few years later, this time recording activity in both the same part of the brain he had before (the hippocampus) and also the visual cortex, the part of the brain that processes visual information. Again, the rats’ neurons fired in the same sequences during sleep as they had when the rats were in the maze, replaying the events of the day. And this time, the replays were coordinated in both parts of the brain Wilson was looking at, reflecting the same experience.
“When the hippocampus replayed these little sequences, the visual cortex also replayed the corresponding visual perceptions,” Wilson says. “So the animal was quite literally seeing what it was replaying from memory. For me, that constitutes the necessary ingredients for referring to this as the equivalent of dreaming in animals. They're experiencing things and they're also perceiving what those experiences were.”
While no one has done a similar study in dogs, scientists have found other evidence that animals dream while working with cats. Several different scientists have prevented cats from becoming paralyzed—either chemically, or by removing the Pons Varolii—during sleep to see what would happen. While in REM sleep, the cats didn’t lie peacefully like they normally would. They actually got up, walked around and moved their heads as if tracking an object. A few even behaved aggressively and pounced on invisible objects, as if they were sleep-hunting mice.
“Increasingly, we're seeing that sleep and its functions, and very likely dreams, are something that are probably quite ubiquitous,” across the animal kingdom, Wilson says.
What Do Dogs Dream About?
The research with rats and cats suggests that animals’ dreams are about the things that animals do when they’re awake. “The dream experiences can be traced back to real experiences,” Wilson says. “It’s memory that’s being used to synthesize the content of the dreams.” In that case, dogs likely dream about their day-to-day experiences, like chasing balls, playing with their humans and exploring their surroundings.
The memory- and experience-based content of dreams gives us a clue about why animals have dreams. “Dreams are made from memories and experience, but it’s not simply memory of experience,” Wilson says. The replays are often broken up into little pieces that are put together in different ways. They create, he says, “new scenes built from old content that can be used to convey, emphasize, highlight or otherwise capture some kind of meaningful point.”
Similar to how movies are made by editing footage together to tell a story, Wilson thinks dreams are memories chopped up into pieces and reassembled into useful scenes that help animals learn about their experiences and surroundings.
Should You Wake Up a Dreaming Dog?
When your dog is in REM sleep (look for twitching of the facial muscles and, as the name suggests, rapid movement of the eyes), whether dreaming or not, it’s best to do as they say and let sleeping dogs lie. It’s not so much that interrupting the dream is bad, but pulling a dog abruptly out of REM sleep can be startling for them, which might confuse the dog or provoke an aggressive reaction. At the very least, you’re interrupting an important part of the sleep cycle, and robbing your dog of some well-deserved rest.
Dreaming or Medical Condition?
When a dog is in REM sleep, you may notice them flicking their paws, twitching their legs, whimpering or making other noises. These are all normal behaviors. The smaller muscles aren’t paralyzed during REM sleep like the major muscles are and these movements may indicate that your pup is having a dream.
“Dogs just have a lot more movement in their sleep than other species, so they’ll routinely paddle their paws and flop around a little bit with their limbs,” says veterinarian Joan Hendricks, dean of the School of Veterinary Medicine at the University of Pennsylvania. “They're just more vigorous. That's all normal.”
If you’re worried that you might confuse these behaviors with signs of a sleep disorder or more serious health issue, take comfort in knowing that these noises and motions are noticeably different from anything that should be a concern. “Normal sleep behavior in dogs is pretty dramatic, but still pretty distinct from a seizure,” Hendricks says. During a seizure, the body movements tend to be faster and more pronounced, and unlike a dream-filled nap, you can’t bring a dog out of it by calling their name.
A sleep disorder like REM behavior disorder is also very distinct. “That comes from not having that normal paralysis fully enforced,” Hendricks says. Like the cats in the experiments, animals with this disorder will get up and walk around (and in the case of one feline patient Hendricks saw, go to the bathroom) while still sleeping. That’s certainly more extreme behavior than few paw paddles or tail twitches. If you think your dog may have a sleep disorder or other medical issue, your veterinarian can help you diagnose the problem and come up with a plan to keep your pet safe while they’re sleeping.
Image: NotarYES via Shutterstock