7 Things You Didn’t Know About Sleep
1. You sleep in cycles.
A full sleep cycle takes about 90 to 120 minutes, says psychologist Lisa Medalie, a behavioral sleep specialist at the University of Chicago. You go through four stages, starting with the lightest one and ending with rapid-eye movement (REM). “Usually people wake up for a couple minutes after each complete sleep cycle,” she says.
2. You become a cold-blooded animal during REM sleep.
During dream-filled, REM sleep, your body isn’t its own furnace. “We lose the ability to thermo-regulate ourselves,” says Mark Mahowald, professor of neurology at the University of Minnesota Medical School and a visiting professor of psychiatry and behavioral medicine at Stanford University. But that’s fine because REM periods typically last only 20 minutes or so, though they can be as short as two minutes or as long as 45, says sleep researcher Ursula Voss, a psychology professor at the University of Frankfurt. “You become a cold-blooded animal. You don’t sweat in REM sleep.”
3. You get less REM sleep when you feel uncomfortable or in danger.
“When you feel unsafe or cold in your sleeping quarters, you don’t enter REM sleep or get as much of it,” says Voss. “Your body automatically adjusts so you don’t go into that stage. REM is a deeper sleep, and it’s more dangerous.” That explains why kids living on the streets get very little REM sleep, she notes.
4. Alcohol reduces REM sleep.
Booze is a sleep-inducing depressant that interferes with shut-eye. “The alcohol puts you to sleep, but it lightens your sleep and suppresses your REM sleep,” says pharmacist Keith T. Veltri, clinical pharmacy manager of Montefiore Medical Center. You may still remember dreams, though, since the alcohol causes increased arousals – and you can only recall a dream when you awake during it. When alcoholics stop drinking, they experience a “tremendous increase of REM sleep, and therefore, more vivid dreaming,” says Mahowald.
5. Some medicines interfere with sleep habits.
Benadryl (or diphenhydramine), the active “PM” ingredient in over-the-counter drugs, may result in shortened REM and fewer dreams, says Veltri. Prescription drugs that can cause nightmares include beta-blockers, which are usually prescribed for high blood pressure; the Parkinson’s disease drug, Sinemet; and the smoking-cessation medication, Chantix. Some drugs, such as antidepressants and barbituates, also reduce REM sleep.
6. Babies in the womb are almost exclusively in REM sleep.
In the womb, fetuses are almost exclusively in REM, which may be very “important for brain development,” says Mahowald. However, they presumably lack memories to consolidate into nighttime visions. “They can’t be dreaming because they have no experience to generate dreams,” he says. Babies spend 50 percent of their shut-eye time in REM. Toddlers are down to 25 percent, and seniors are down to about 15 percent.
7. Not all animals experience REM sleep.
Dolphins and whales don’t. “It has something to do with their aquatic environment,” says Jerry Siegel, professor of psychiatry and director of the Center for Sleep Research at UCLA. Fur seals experience REM and non-REM sleep when they’re on land but next to no REM sleep when they’re in the water, he says. REM sleep may play no role in intelligence. “The platypus has spectacular REM sleep,” says Siegel. “This is an animal that has a tiny little brain.” If REM sleep were cognitive, he says, “humans wouldn’t fall in the middle.”