Sleeping Dogs and Other Mysteries.

I just finished reading a book* about how the mind works, and the mystery of consciousness. It touched on some similarities between a particular stage of sleep called "slow wave sleep " and epilepsy. In each case, there is a loss of consciousness and the brain waves become relatively slow, more coordinated, and rhythmic. A big difference is that in an epileptic seizure there is major rhythmic muscle movement. (* "A Universe of Consciousness," Gerald M. Edelman and Giulio Tonini, Basic Books, 2000)

Current scientific consensus seems to be that dogs and cats, though conscious, do not have the same kind of consciousness that humans do. Our consciousness includes a very well developed self-image. We spend more time thinking about ourselves and dogs and cats spend more time sleeping.

According to other references I was able to dig up, dogs spend from 10 to 16 hours sleeping every day, and cats spend about the same. I think this varies quite a bit depending on what is going on in the environment. Cats and dogs, like older humans, tend to get drowsy and doze off if there is not something to make staying awake worthwhile.

Human sleep has been extensively studied and can be divided up into five stages, each of which lasts about 10 minutes. By keeping these in mind, you may understand some of your own sleep patterns:

1. The first stage is relaxed wakefulness. As the body prepares for sleep, muscles are tense at first and then relax, and the eyes move erratically, then slow down to a roll.

2. Stage 2 is light sleep. The muscles alternate between tension and relaxation, the heart rate slows, and body temperature decreases.

3 & 4. These are deep sleep stages. The electrical activity of muscles and nerves is relatively slow and rhythmic, like that of epilepsy.

Normal sleep progresses through stages 1,2,3, and 4, and then in reverse - 4,3,2, and 1, in about 90 to 120 minutes. Then you go into stage 5, "Rapid Eye Movement" or "REM" sleep.

5. In REM sleep, the eyes rapidly dart back and forth, as though you were watching a frantic ping pong game. Heart rate and respiration speed up. The muscles of the face, fingers and legs may twitch, but major muscle movements are inhibited - a sort of paralysis. Intense dreaming occurs during REM sleep and the paralysis of major muscles is thought to protect the dreamer. In some sleep disorders this paralysis does not occur, and the person may dream about running and actually jump up out of bed and run into the wall. The length of REM sleep varies from 10 minutes, early in the night, to an hour, later on. These five stages of sleep make a cycle, and a typical person may go through five cycles through the night, each cycle a little longer than the one before.

I couldn't find as much detail about sleeping in dogs and cats, but they both go through "Slow Wave Sleep" and "REM" sleep stages. In cats, studies have shown that the transition in the environment from dark to light, as well as from light to dark, tends to make them wake up.

In another study, dogs spent about twelve hours a day in alert wakefulness, a couple hours in a "drowsy state," a couple of hours in "slow wave sleep," and about an hour in REM sleep. You have probably seen your dog in REM sleep - whining softly with all four legs weakly twitching. As for your cat, you've more likely seen him in deep slow wave sleep.