How Sleep Works
A Guided Tour
Stage R: Rapid Eye Movement
Your brain waves tell the tale: The delta waves from stage 3 are history. In their place is a strange mixture of low-amplitude theta waves interspersed with some alpha and beta wave activity. This is the definitive wave form of REM sleep with its distinctive “sawtooth” pattern. And it looks nothing at all like the other stages of sleep. In fact, it looks a lot like the brain waves seen in wakefulness.
Your breathing and heart rate are relatively rapid and your blood pressure, metabolism and body temperature are all going back up. Your eyes are still closed but they’re darting around, back and forth, up and down in the classic Rapid Eye Movement pattern. An incredible amount of neurological activity has sparked to life inside your head.
REM is sometimes called “paradoxical sleep,” and a paradox it is indeed: You look, for all the world, like you’re in a very deep sleep, but your slumbering body conceals a brain that has shifted into high gear.
In some ways, your brain is even more active now than when you are awake. An intense barrage of electrical activity is traveling up from your brainstem into your forebrain, all the way to the highest centers of your cerebral cortex. Your brain continues to keep itself cut off from the outside world, isolated from external stimulation. Instead it is producing its own stimulation, generated entirely from within.
Many scientists believe that this is what makes us dream. The random pulses of electrical activity are happening in such a way that they mimic incoming sensory information, which your brain simply interprets as real. Your mind sort of makes up stories to go along with it. There happens to be a very strong association between REM and dreaming which comes down to this statistic: If you wake someone up out of REM sleep, they’ll report dreaming about 80 to 90% of the time. This compares to only about 30% during NREM.
Our bodies have evolved a very important safety feature to go along with dreaming. While you are in REM, your muscles become paralyzed so you won’t “act out” your dream. All nerve signals to the muscles (except for involuntary functions such as breathing and heartbeat) are cut off in the brainstem.
We must give mention to one more feature of REM: a very strange phenomenon called nocturnal penile tumescence (NPT) or nocturnal erections. In male sleepers, for reasons scientists haven’t quite discovered, REM causes the penis to become erect. Snicker if you will, ladies, but the same thing occurs in females too, though in a different form: the clitoris becomes erect, the vagina lubricates, and even the nipples become hard. Now, you might conclude from all of this that the sleeper must be having a really good dream! But that isn’t what’s happening here. The effect is most likely just due to the way REM activates the autonomic nervous system causing increased blood flow to said regions. Ironically, this turns out to be one of the few aspects of life that has nothing to do with sex!
You’ve been in the REM state for about 10 minutes now, and you’re just about to come out of it. This first episode of REM is usually a very short one. They get progressively longer with each successive sleep cycle, lasting as long as 60 minutes toward the end of the night. Overall, you’ll end up spending about 20 to 25% of your night’s sleep in REM.
Just exactly what REM is all about — how it evolved and what purpose it serves — is one of the most hotly debated questions in sleep science. Three theories predominate: The first is that our brains use REM to consolidate new memories and learning into our long-term memory banks as we sleep. Another fascinating theory is that REM provides the brain with stimulation during long stretches of sleep by periodically activating the central nervous system. Other scientists believe that REM may serve to jumpstart the development of the brain in newborn babies. As for dreaming, the strange kaleidoscope of dreams we experience every night may be nothing more than an incidental effect of REM. As one expert puts it, dreams may be “just the foam on the beer.”
If you’re interested in a bit more depth, you can read our full article on REM Sleep.
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