Stages of Sleep: REM and Non-REM Sleep
What Is REM Sleep?
Usually, REM sleep occurs 90 minutes after sleep onset. The first period of REM typically lasts 10 minutes, with each recurring REM stage lengthening, and the final one may last up to an hour. Polysomnograms show brainwave patterns in REM to be similar to that recorded during wakefulness. In people without sleep disorders, heart rate and respiration speed up and become erratic during REM sleep. During this stage the eyes move rapidly in different directions.
Intense dreaming occurs during REM sleep as a result of heightened brain activity, but paralysis occurs simultaneously in the major voluntary muscle groups. REM is a mixture of encephalic (brain) states of excitement and muscular immobility. For this reason, it is sometimes called paradoxical sleep.
The percentage of REM sleep is highest during infancy and early childhood. During adolescence and young adulthood, the percentage of REM sleep declines. Infants can spend up to 50% of their sleep in the REM stage of sleep, whereas adults spend only about 20% in REM.
How Much Sleep Do You Need?
The amount of sleep a person needs depends on the individual. The need for sleep depends on various factors, one of which is age. Infants usually require about 16-18 hours of sleep per day, while teenagers need about 9 hours per day on average. Most adults need about 7-9 hours of sleep per day.
The amount of sleep a person needs also increases if he or she has been deprived of sleep. People do not seem to adapt to getting less sleep than they need.
What Are the Consequences of Too Little Sleep?
Too little sleep may cause:
- Impaired memory and thought processes
- Decreased immune response
- Increased pain
Sleep deprivation also magnifies alcohol's effects on the body, so a fatigued person who drinks will become much more impaired than someone who is well-rested. Sleep deprivation also increases pain perception on pain-simulation testing. Caffeine and other stimulants can temporarily overcome the effects of severe sleep deprivation, but cannot do so for extended periods of time.