Reviewed by Jenna Gress Smith, PhD
The singular activity we know as sleep is actually made up of 4 sleep stages, which together form the building blocks of a full sleep cycle. During stages 1 to 3, which include light and deep sleep and are referred to as NREM sleep, our heart rate and body temperature gradually drop and our brain waves slow down as our sleep progresses.
The fourth sleep stage is known as REM, or rapid eye movement, sleep.
What is REM sleep?
REM sleep gets its name because during this stage, your eyes dart back and forth behind your closed lids. Unlike the other sleep stages, which are characterized by slowed brain waves, your body’s physiological markers are similar to those when you’re awake: Your heart rate and blood pressure quicken to near waking levels, your breathing speeds up, and your brain activity is buzzing.
Because it’s so different from the other sleep stages, REM sleep is often referred to as paradoxical sleep, or desynchronized sleep.
REM sleep is also when your most vivid, fantastical, and occasionally terrifying dreams occur—and the ones you’re most likely to remember. While you’re in this sleep stage, an area at the base of the brain called the pons sends signals that shut off neurons in the spinal cord, temporarily immobilizing your muscles and limbs. This prevents you from acting out your dreams—for instance, running headlong into a wall if you’re dreaming you’re being chased.
And though there’s no consensus among sleep experts as to why we dream and what our dreams mean, there is agreement that REM sleep has a huge role in our learning and memory processes, and our emotional regulation.
Why is REM sleep important?
REM sleep keeps your brain sharp
REM is considered the mentally restorative sleep stage. During REM sleep, the areas of the brain that are essential for learning and making or retaining memories are stimulated; it's when your brain consolidates, processes, and stores new information.
Psychologist Rubin Naiman, a sleep and dream specialist at the University of Arizona Center for Integrative Medicine and the author of a paper about REM sleep deprivation (Annals of the New York Academy of Sciences), described the brain during REM sleep as a kind of “second gut” that digests all the information gathered that day. “Everything we see, every conversation we have, is chewed on, swallowed, and filtered through while we dream” and either assimilated or discarded, he said.
REM sleep also sharpens your concentration and focus, which helps you optimize your performance at work, while playing sports, or working out— in every aspect of your life, really. Research suggests that when people are deprived of REM sleep they have trouble recollecting things they’re taught before falling asleep.
Here’s how James B. Maas, PhD, a leading authority on sleep and performance, put it: “During REM sleep, the brain busily replenishes neurotransmitters that organize neural networks essential for remembering, learning, performance and problem solving,” he explained. “Conversely, depriving the brain of sleep "makes you clumsy, stupid and unhealthy."
REM sleep supports emotional health
Besides supporting memory and mental focus, REM sleep has a major impact on your mood and your emotion processing. That’s because your amygdala, the same part of your brain that helps you make decisions and form memories, also processes emotions. And it activates during REM sleep.
You’ve probably experienced how even a single night of poor sleep will leave you feeling irritable, moody, and more emotionally reactive. Several studies, confirming what you already know, suggest that REM sleep can affect how accurately you read emotions and process external stimuli.
Matthew Walker, PhD, professor of neuroscience and psychology and director of the Center for Human Sleep Science at UC Berkeley, is the author of the groundbreaking book Why We Sleep. Walker and his colleagues have found that people who view emotional images before getting a good night’s sleep react less intensely to the same images the next day, compared to those who didn’t sleep well. “I think of dreaming as overnight therapy,” Walker said. “It provides a nocturnal soothing balm that takes the short edges off of our emotional experiences so we feel better the next day.
“We know that during REM sleep there is a sharp decrease in levels of norepinephrine, a brain chemical associated with stress," he said. "By reprocessing previous emotional experiences in this neuro-chemically safe environment of low norepinephrine during REM sleep, we wake up the next day, and those experiences have been softened in their emotional strength. We feel better about them, we feel we can cope.”
A meta-analysis of experimental sleep deprivation studies confirms this, finding that sleep loss had an even greater effect on emotions than on cognitive or motor function.
When does our REM sleep occur?
You will usually enter REM sleep about 90 minutes after you first fall asleep.
REM sleep stages tend to be shorter during the first two-thirds of the night when the body prioritizes deeper, slow-wave sleep. With each new sleep cycle, you’ll spend increasing amounts of time in REM, with most of your REM sleep happening during the second half of the night.
Because longer periods of REM sleep occur during the final hours of sleep — in the early morning, for most people — it can get cut off when you don’t spend a full seven or eight hours in bed. Meaning it’s the first to go when you set a morning alarm.
How much REM sleep do we need?
Most adults spend approximately 20 to 25% of their time asleep in the REM stage. But this is a ballpark figure, not set in stone, and can change over time and for many reasons. For instance, the percentage of REM sleep you get typically declines with age.
Your sleep patterns and sleep duration not only change throughout your life, but even from day-to-day. How much time you spend in a particular sleep stage, including REM, can vary based on what your body needs on any given night.
How to get more REM sleep
The best way to get more REM sleep is … to get more sleep. Or rather, more high-quality sleep. Aim to hit that sweet spot which for most people is 7 to 9 hours, but keep in mind that the best sleep is continuous, and non-fragmented. Which means that 7.5 hours of solid sleep is better than 9 hours with awakenings for most people.
Whatever you can do to improve your sleep—better sleep habits and behaviors—will also boost your time in REM. There are, however, a couple of things you can do to optimize your REM sleep:
- Maintaining a consistent sleep schedule, which means going to bed at the same time each night and waking at the same time each morning. This will maximize the quality of your sleep, including REM sleep.
- Research shows that even moderate alcohol intake in the evening can disrupt your sleep cycle, and interfere with REM sleep. If your body is still processing the alcohol when you go to bed, it has a hard time getting past light sleep and into the deeper sleep stages. A few drinks close to bedtime can delay entering the first REM phase and reduce the number of REM sleep phases overall.
- Certain medications and medical conditions such as sleep apnea, can affect sleep quality and impact REM sleep. Addressing these conditions may help improve the overall quality of your sleep.