What Is REM Sleep?

Rapid eye movement (REM) sleep is a unique stage of sleep characterized by random rapid movement of the eyes (via Medical News Today). During this phase, your body undergoes a number of physical and neurological changes, including increased brain activity, elevated heart rate, fast and irregular breathing, rapid eye movement, high blood pressure, changes in body temperature, increased oxygen consumption by the brain, sexual arousal, and twitching of the face and limbs.

Your first REM cycle occurs around 90 minutes after you fall asleep and usually lasts for 10 minutes. As the night goes on, each REM cycle will get progressively longer and recur every 90 minutes. Since REM sleep is associated with increased brain activity, it is common to experience vivid and intense dreams during this stage of sleep. Because of the intensity of these dreams, your muscles are immobilized to prevent you from acting out your dreams, leaving your limbs temporarily paralyzed. As a result, REM sleep is also sometimes referred to as paradoxical sleep.

REM sleep is crucial to your overall health and plays an important role in brain function and development. For instance, REM sleep can impact your memory (via Shape). Studies have shown that REM sleep benefits learning and memory by allowing you to process new memories and maintain essential neural pathways responsible for learning and creating new memories.

"During sleep, your brain is sort of replaying certain things you've experienced and trying to figure out if it should put that experience into your short-term or long-term memory-or to just forget about it," Dr. W. Chris Winter, a sleep specialist and neurologist, told Shape. "Unlike deep sleep, which is really concerned with rest and recovery, REM sleep has lots more to do with concentration, focus, memory consolidation, and pain perception."

REM sleep can also impact brain development in infants (Verywell Mind). That's because the increased brain activity that occurs during REM sleep is responsible for developing and strengthening mature neural connections.