The mysterious phase of deep sleep when our most vivid dreams occur has long fascinated scientists and artists. But it wasn't until the 1950s that sleep period -- also known as rapid eye movement, or REM, sleep -- was actually discovered and documented in a lab.
You've certainly heard the term REM before, but do you really know what it is -- and what's going on in your brain during this critical time?
During a typical night's sleep, the brain goes back and forth between REM and non-REM sleep roughly every 90 minutes to two hours, with each cycle lasting anywhere from 10 minutes to an hour. The first REM cycle is generally the shortest of the night, and starts at least an hour and a half after you hit the hay.
As the name would indicate, it's common for your eyes to rapidly move around in your head during REM sleep. Your heart rate and breathing quicken as well. But there's much more to REM than than these small physical changes.
Here are seven surprising things you should know about REM sleep:
1. Your eyes are "looking" at something when they move.
In a sense, your eyes are "seeing" different things when they're darting around during REM sleep. It's likely that a new image forms the mind's eye every time you move your actual eyes, according to a study published in August in the journal Nature Communications. In other words, you may be looking at objects in your dreams.
"It is extremely interesting… that these eye movement produce something like visual processing during dreaming," psychiatrist Michael Czisch of the Max Planck Institute of Psychiatry in Germany told New Scientist.
2. Alcohol and drugs mess with your REM.
Although alcohol often helps people fall asleep faster and sleep more deeply, a 2013 study found that it can get in the way of REM sleep. The study's authors found that a drink or two probably won't affect your sleep, but there's a good chance that more than that will cut into REM time.
This helps explain why you may not feel very rested after a night of drinking, even if you've slept as long as you usually do. Drugs like antidepressants and stimulants can also interfere with REM in both adults and children.
3. This sleep phase is critical for the developing brain.
REM converts daily experiences into long-term memories in a child's brain, and helps make those experiences "stick," suggests a study that published in the journal Science Advances in July. These key brain functions are disrupted when a child doesn't get enough REM sleep.
"There is a lot of data accumulating that says the amount of sleep a child gets impacts his/her ability to do well in school," Marcos Frank, professor of medical sciences at Washington State University Spokane and one of the study's authors, said in a statement. "This study helps explain why this might be -- and why we should be cautious about restricting sleep in our children."
4. It can enhance creative problem-solving.
If you need to come up with a creative solution, try sleeping on it -- REM sleeping on it, that is. A 2009 study found that REM sleep "directly enhances creative processing" by stimulating brain networks that allow for new and unusual associations between seemingly unrelated ideas.
"We found that -- for creative problems that you've already been working on -- the passage of time is enough to find solutions," Sara Mednick, a psychiatry professor at University of California, San Diego and the study's lead author, said in a statement. "However, for new problems, only REM sleep enhances creativity."
5. A rare disorder can cause people to act out their dreams.
REM sleep behavior disorder occurs when people act out vivid dreams while asleep -- as many as four times per night. It can become dangerous for a sleeper or bed partner when the dreams get violent: Common actions include jumping, flailing, shouting, kicking and punching.
6. REM sleep paralyzes you.
Your skeletal muscles become paralyzed during a period of REM -- that's right, you can't move at all. Scientists have found that two powerful brain chemical systems work together to cause REM sleep paralysis.
This improved understanding of how muscles become paralyzed during REM sleep may one day help scientists to better treat narcolepsy, tooth-grinding and REM sleep behavior disorder.
7. Lack of REM sleep is linked with neurodegenerative disorders.
Losing out on REM sleep can contribute over time to the development of neurodegenerative diseases like Alzheimer's and Parkinson's. Scientists have suggested that poor sleep (particularly, not getting enough REM sleep) may contribute to toxic proteins building up in the brain, attacking long-term memory storage and triggering Alzheimer's disease.
Why do we dream during REM sleep? Check out the "Talk Nerdy To Me" episode below to learn more.