DURING SLEEP YOUR BODY AND MIND SWITCHES THROUGH DIFFERENT STAGES
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THE STAGES OF SLEEP
Sleep is not a uniform state. During the night we pass through several different stages. Scientists distinguish between four different sleep phases and two different types of sleep: REM and non-REM sleep, which are repeated periodically throughout the night.
With an EEG (electroencephalogram) it is possible to track the individual stages of sleep accurately using brain waves.
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REM SLEEP
REM means "rapid eye movement" and is used to describe the short periods when the eyes move rapidly under the closed lids. The sleeper's muscles are completely motionless, but the brain is working at full speed, producing vivid dreams and deep emotions during this phase.
During the night we alternate between REM and non-REM sleep and each cycle lasts between one and one-and-a-half hours. Initially REM sleep only lasts for about five minutes, but this phase can be as long as 50 minutes later in the night. At the same time the proportion of non-REM sleep falls, so that the individual cycles still last between one and one-and-a-half hours.
Scientists believe that the different phases of sleep support different memory functions. REM sleep is supposed to promote unconscious learning processes, such as acquiring motor skills. In contrast, deep sleep helps the higher cognitive functions and plays an important role in allowing the brain to memorise facts or solutions to difficult tasks. This is one of the reasons why it is easier to remember things that you have learned in the morning.