There are three majors measures of sleep that are used in the sleep laboratory; brain waves, eye movements and muscle tone. In Figure 1 waking is compared to the two basic categories of sleep: NREM and REM sleep. Some of the major markers of these differences which are apparent with this kind of very brief look at a polygraph record is the eye movement activity, which in rapid eye movement (REM) sleep is quite intense. Certainly relative to NREM sleep, and even much more variable and dense than during waking. Muscle tone is also quite interesting. Waking muscle tone is high relative to NREM muscle tone which is moderate, but what’s interesting about REM is that there is virtually no muscle tone. For all practical purposes you’re paralyzed!
When you go to bed at night, you sort of snuggle into your favorite sleeping position. You may be a side person or a back person or sleeping on your stomach may be the only way for you to settle in. Once you get yourself settled in Figure 2 shows the sequence of events that occur in sleep. You start in light sleep at point “A” while point “B” is deepest sleep. There are several features I’d like to point out on this figure. First you cycle between light and deep sleep throughout the night, about every hour and a half. This hour and a half circadian rhythm we actually experience throughout the twenty four hour day and thus it simply continues into sleep. It’s particularly noteworthy in sleep because of the movement into what is called rapid eye movement sleep (REM). It is associated with dreams but this association is not absolute. You can see at “C” that there is mental activity that we might call dreams that occur in non-rapid eye movement sleep (NREM). So although there are some dreams, for the most part, they are clustered in the REM episodes.
Furthermore, the dreams of REM sleep are phenomenologically quite distinct from those in NREM sleep. There’s been an argument in the dream research literature about whether or not REM sleep is the biological marker for dreams. That’s what it was touted as when first discovered in the early 1950’s. Then with subsequent research sleep and dream scientists got disillusioned with that simplistic isomorphism and concluded that dreams go on all night long to one degree or another, they simply cluster in REM.
As is often the case in science, we have gone almost full cycle and realize that there are real phenomenological markers of mental activity during REM that are quite distinct from mentation during NREM sleep. One difference is bizarreness. In a recent article by Harry Hunt in the journal Dreaming, he was able to show that attempts to equate the bizarreness of REM sleep mentation to the bizarreness of NREM sleep mentation doesn’t work. In other words, REMing dreams are distinct from NREMing dreams.
Lets return to Figure 2. You can see at “D” that REM episodes get longer as you go through the sleep cycle. Therefore most of your dreaming happens late in the sleeping cycle. Those dreams which last from 30 to 40 minutes have the elaborate story lines and complex shifts and transitions which we call bizarreness. Your mother’s got a purple face. Tin cans are growing out of people’s heads. That’s the kind of stuff you are experiencing during these early morning hours. That’s the kind of stuff that “real” dreams are made of!
There you are paralyzed from the neck down, your eye movements are jerky and rapid, your heart rate fluctuates, your breadth rate changes. Sometimes when you wake up from an especially intense REM episode you may be panting, your heart’s pounding and you’re sweating. And you mutter, “Thank God, that was only a dream!” If that happens you have come out of rapid eye movement sleep. So for instance, if you’re an ulcer sufferer there are twenty times the amount of stomach acid secretions during REM than during NREM. If your child has asthma and they wake up with an asthma attack, they’re likely waking from REM sleep. If you have angina, these heart problems are going to occur most likely out of REM sleep. In other words, REM doesn’t seem to be really good for your health. It stresses the body. It pushes all these different systems more so than while awake. Not while your jogging ten miles, obviously, but this whole system is going to be really revved up in the main more so than while awake. In addition, while all these systems are on over-drive, the brain is increasing its activity. What is going on?