Our dog is asleep at our feet when suddenly his feet begin to twitch and he starts to paddle as if running or swimming. Is he dreaming, and if so–what about? Chasing a cat through the woods or diving into a river to fetch a stick? Our dog is asleep at our feet when suddenly he cries out or yelps as if in pain but does not wake up. Is he having a nightmare, and if so– what about? Having to go to the veterinarian tomorrow for an injection or not sure where his next meal is coming from? Although scientists still do not really know the true function of dreaming, it seems to be necessary for normal data processing and memory storage. Dogs think and they have memory. And their memory banks need period purging and reorganisation during sleep just as ours do.
Like humans, dogs have two main types of sleep: rapid eye movement (REM) sleep and slow wave sleep (SWS). As a dog falls asleep the first stage he enters is SWS, the "sleep of the mind," in which mental processes are muted but muscle tone remains. The next stage is REM sleep, the "sleep of the body," in which the body is fully relaxed but the mind is racing and the dog's eyes are darting rapidly. In SWS, brain waves are slow, undulating and of high amplitude–similar to those in a lightly anesthetised animal or person. Dogs and humans are more easily aroused from SWS sleep, which appears to be a transitional state with incomplete muscle relaxation. The dog lies still and is oblivious to his surroundings; his breathing slows; his blood pressure and body temperature drop; and his heart rate decreases.
After about ten minutes, your dog enters the rapid eye movement (REM) or active stage of sleep. In REM sleep brain waves are rapid and irregular, like those of the "awake" state. During REM sleep dogs show evidence of heightened mental activity–fast electroencephalogram [EEG] (brain wave) pattern. They may move their legs as if they are running, may whine or whimper as if excited, and may breathe rapidly or hold their breath for short periods. When REM sleep is achieved they are at their most relaxed and are most difficult to waken. It is during this more profound physical sleep that their eyes begin to dart and the brain waves pick up pace. Humans awakened from this state report that they have been dreaming; dogs are probably dreaming, too, when they are in REM sleep. (Although no dog has ever told anyone about a dream he's had.)
Adult dogs spend about 10 to 12 per cent of their sleeping time in REM sleep. Puppies spend a much greater proportion of their sleep time in REM sleep, no doubt compacting huge quantities of newly acquired data. The truth that we're certain about is that our dogs sure know how to sleep. The amount of time spent napping varies from dog to dog and depends on the dog's age and personality. Counting little naps and longer snoozes, most dogs sleep about 14 hours a day. Nobody is sure why dogs sleep so much. The amount of sleep that an animal needs depends upon its species. Horses and cows may sleep only three or four hours daily because they require long hours of grazing to supply their bodies with sufficient food. Bats and opossums may sleep closer to 20 hours.
The various breeds of dogs also seem to have different sleep requirements. Dogs sleep more than we do, but they wake more frequently than we do. How much and when they sleep depends on the level of activity in their environment. A dog living as a pet in the home is likely to sleep more than a dog that works for a living, like a search-and-rescue dog or a dog working on a farm. Dogs are lucky–they are able to adjust their sleep pattern so that they can be awake when there is something to do, and asleep the rest of the time. Of course, today's modern indoor dog sometimes sleeps out of boredom. You can help your pet by providing plenty of stimulation during the day–this can be in the form of environmental enrichment, a companion or plenty of walks and playtime with you. If he has enough to do during the day, he may stay awake when the sun is up and sleep at night when you do.