It can be fun to watch our dogs sleep; they move, growl, yip, and bark while snoozing, and they look so cute. Are they dreaming of chasing and playing? Or is there something else going on in their mind?
The brain of a dog is very similar to that of people in terms of structure and function. Electroencephalograph (EEG) technology has allowed scientists to study the sleep patterns of dogs. Although dogs sleep more than we do, they have the same sleep phases as humans. They too have rapid eye movement (REM) sleep as well as slow-wave deep sleep.
Given that dogs have highly complex brains and exhibit the same electrical impulse sequences as humans when they sleep, it is safe to assume that dogs do in fact dream, and veterinary neurologists agree. But of what do they dream? To try to work this out, scientists temporarily deactivated a portion of the brainstem called the pons. The pons helps to inhibit the movement of large muscle groups such as those in the legs. Before the pons had been temporarily deactivated, dogs in the study showed the usual leg twitching behavior that we see when dogs are asleep. However, after deactivation, dogs were much more physical in acting out their dreams, such as pointing at imaginary squirrels, playing with imaginary dogs, and defending the house from phantom burglars.
In some (rare) cases, dogs can have sleep disorders that are similar to ours. One condition in people that appears also to manifest itself in dogs is REM behavior disorder. In this disorder, dogs' movements are more violent and their vocalizations louder. For the most part, there's no harm to the dog unless they roll off the bed or otherwise get hurt while they thrash their legs. It is more disturbing for the pet parent but there are treatments that can help.
It's true that dogs spend a lot of their time snoozing. How much sleep a dog needs varies by age and even breed. A puppy, especially one that is experiencing a growth spurt, can sleep up to twenty hours per day. The average adult dog naps for around fourteen hours per day, but giant breeds such as the Saint Bernard and the Newfoundland seem to need more sleep, regardless of their age. These dogs nap for large periods of the day, spending up to eighteen hours resting (which is partly why these large dogs are happy to live in an apartment or a home with a small back yard)! As dogs get older, they can again sleep up to twenty hours per day as their metabolism slows down.
Do dogs really need this much sleep? Other than puppies and seniors, the answer is likely no. However, dogs have evolved from wolves which were designed to be doing something whether that be resting, working, traveling, or on the hunt for food. There are large periods of time where our pet dogs don't have anything useful to do, so this time is filled with sleep. Working dogs, such as police canines or assistance pets, do not sleep as much as house pets, yet there are no adverse effects on their health.