REM sleep stands for Rapid Eye Movement which is the fifth stage of sleep. Normal sleep patterns cycle through five stages of sleep. It takes the average person 90 to 120 minutes to cycle through all five stages of sleep. During a normal eight hour night, a person will cycle through all five stages four to five times. During stage one sleep, a person sleeps lightly, drifting in and out. The muscles twitch as they relax and a person may even feel like they are falling slightly. In the second stage of sleep, the brain relaxes and eye movement ceases.
Stage three sleep is the beginning of deep sleep. Delta waves are high amplitude brain waved with a frequency of 1–4 Hertz which can be recorded with an electroencephalogram. The body does not move. During stage four, the brain produces delta waves exclusively. It is very difficult to wake someone when they are in stage four sleep. Children may experience bedwetting, sleepwalking or night terrors during stage four sleep.
What Happens in REM Sleep?
Stage five is when REM sleep occurs. This is the most active part of sleep. The brain and the body become very active during REM sleep. REM is also when dreaming occurs. According to sleep studies, brain waves increase during stage five. Brain activity during REM sleep is similar to those experienced during waking hours.
The stage takes its name from the physical movement of the eyes during this stage of sleep. The eye movement speeds up although the limbs become paralyzed. Internally, the heart rate and respiration increase and blood pressure rises. Internal body temperature fluctuates; some people may become cold while others become hot. Men can experience erections during this stage of sleep.
When a person wakes and remembers their dream they are often waking from REM sleep. The average adult spends only about 20 percent of their sleeping period in REM sleep while babies spend over 50 percent of their sleep in REM. Babies average a longer sleep cycle and sleep more frequently than adults do, but REM is a time for processing information. Babies are learning constantly and require greater time spent in processing and storing information.
Over the average lifespan, time in REM sleep diminishes. The elderly spend 15 to 18 percent of their sleep in REM while spending more and more time in the second stage of sleep.