Humans need sleep in order to maintain health and proper function. The human body is programmed to sleep as a way to restore our minds and bodies. Two different systems, the sleep wake homeostat and the internal biological clock, determine the timing of our sleep patterns. These factors also explain why we can stay awake during the day and sleep at night. In the past, sleep was considered a passive state in which the brain and body turned off but scientists have since discovered that the brain goes through different patterns of activity during each period of sleep.
It wasn’t until the late 1920’s that a device was invented that allowed scientists to record brain activity. This led researchers to learn that the brain was actually highly active at times during sleep. This discovery led to further research that revealed two main types of sleep that were defined by certain electrical patterns in the brain of someone sleeping, as well as the absence or presence of eye movements. The two types of sleep are called rapid eye movement (REM) sleep, and non rapid eye movement (NREM) sleep. REM sleep is generally referred to as active sleep during which the brain is highly active and there is eye movement. There are sleep experts that believe these eye movements are somehow related to dreams. Often, when people are woken up during REM sleep, they report having vivid dreams while those woken during NREM sleep report dreams with much less frequency. It has also been discovered that muscles in the legs and arms are temporarily paralyzed during REM sleep. It is thought that this is a neurological reaction that prevents people from acting out their dreams.
NREM sleep consists of three different stages including N1, N2, and N3. During the progression of NREM sleep stages, brain waves start to slow and become more synchronized and the eyes stop moving. N3 is the deepest stage of NREM sleep during which the lowest frequency brain waves are observed. N3 is also referred to as slow wave or deep sleep.
Sleep Cycles at Night
In adults, sleep normally begins with NREM, or to be more specific, N1, the first stage of sleep. The transition from being awake to the N1 stage of sleep occurs within seconds to minutes after a person begins to drift off. The N1 stage then lasts approximately one to seven minutes and is followed by the N2 stage of sleep. N2 normally lasts anywhere from 10 to 25 minutes and is followed by N3, or deep sleep. The final stage of NREM typically lasts about 20 to 40 minutes. During the N3 stage of sleep, the brain starts to become less responsive. REM sleep is believed to comprise approximately 20 to 25 percent of total sleep. The REM and NREM stages of sleep continue to alternate throughout the night with the REM cycle becoming longer throughout the night.
Learn More: The Cycles & Phases of the 5 Stages of Sleep
Changing Sleep Patterns
There are many different factors that can affect sleep patterns including amount of recent sleep, age, a person’s internal clock, and the time of night, among other factors. Deep sleep is greatest in young children and begins to steadily decrease with age. Scientists believe that this may have to do with changes in the function and structure of the brain. Missing sleep or keeping an irregular sleep schedule can result in the redistribution of the stages of sleep.
Getting a good night’s sleep is important for health. Scientists continue to study sleep patterns and how they relate to dreams, health, and many other factors.
For More Information on Sleep
- Healthy Sleep – Natural Patterns
- The Different Stages of Sleep
- How to Get a Good Night’s Sleep
- Sleep Stages and Dreams
- Difference Between REM and NREM Sleep
- Sleep and Biological Rhythms
- REM Sleep and Dreaming
- Brain Basics – Understanding Sleep
- The Evolution of REM Sleep
- Memory Consolidation and REM Sleep
- Stages of Sleep – A Sleep Chart
- Stages of Sleep and Brain Waves