With the introduction of the electroencephalogram or EEG, scientists were given a new view into how we sleep and the ability to study sleep in completely new ways.  With the data made available by the EEG and other testing, scientists have formed a comprehensive understanding of sleep and how the different stages of sleep relate to each other.  Here is everything you need to know about the 5 stages of sleep and what is happening in your brain and body at each point in the sleep cycle.

The Beginnings of Sleep – Pre-Sleep
As your body relaxes and you settle in to fall asleep, your brain activity displays a small, fast wave pattern called beta waves. After several minutes you enter that twilight-type state of almost asleep as your body continues to relax and your brain switches to alpha waves.  During this timeframe you may experience hypnogogic hallucinations like feeling as if you are falling or hearing someone call your name.  Myoclonic jerks, the random, sudden startled movement of a body part, also happen during this pre-sleep stage.

Stage 1 – Light Sleep
Light sleep, the transition from being awake to being asleep, is the first official stage of sleep and the beginning of the sleep cycle.  During this stage, your brain shows theta wave patterns on the EEG.  Lasting about five to ten minutes, someone awakened while in this light sleep stage may not even think they have slept.  Stage 1 is only encountered at the beginning of the first sleep cycle when you fall asleep and, unlike other stages, is not repeated over the course of the night.

Stage 2 – Unconscious Sleep
The second stage of sleep lasts for about twenty minutes and is the least active of the sleep cycle stages.  Although your brain waves get much more rapid and are punctuated with rhythmic spindles,  you appear completely unconscious during this stage.  Your body further relaxes and your body temp decreases as your heart rate slows down.  This is the first stage where the brain and body begin to have a divergent experience, the brain becoming more active as the body becomes more passive.

Stage 3 – Deep Sleep
The third stage of sleep is the transition from light sleep to the deepest type of sleep.  Your brain activity shows the deep slow pattern of delta waves during this twenty to thirty minute stage. Depending on the researcher, this stage and stage 4 may be combined as they are nearly identical.

Stage 4 – Deeper Sleep
Often called delta sleep because of the delta wave brain activity pattern captured on the EEG, the fourth stage lasts for about thirty minutes and sleepers in this stage can be very difficult to wake-up.  Parasomnias like bedwetting, night terrors and sleepwalking generally occur during this part of the sleep cycle.  This is the last of the N-REM (non-rapid eye movement) sleep stages.

Stage 5 – REM Sleep
This stage is called REM sleep because of the rapid eye-movements that can be observed while you are in this part of the cycle.  When you enter REM sleep, your respiration and brain activity increases.  Your brain wave patterns resemble those captured when you are awake.  This is the stage where the majority of dreaming occurs.  Also called paradoxical sleep, during this stage your brain and body have paradoxical experiences.

As your brain activity increases, your body relaxes and all voluntary muscles become paralyzed.  Because REM sleep and wakefulness are so similar from the perspective of your brain, this paralysis, called atonia, is necessary to ensure your body does not act out what your brain is dreaming.

The first REM stage is very short, lasting only a few minutes but over the course of the night, each REM stage will last longer than the previous one, shortening the other stages.  By the end of the night, your last REM stage may last as much as sixty minutes.

Cycling Through the Night
Contrary to popular belief, you don’t experience the sleep stages in a continuous linear fashion.  The first cycle generally proceeds from stage 1 to 4 in order, but most people will go back up to stage 3 and 2 before jumping to stage 5 for the first time.  That initial descent to REM sleep usually takes about ninety minutes.  Once the first cycle is complete, you will generally bounce directly back to stage 2 to start the next cycle.  An average night’s sleep, which repeats the cycle pattern 4-5 times over the course of the night, would look like this 1 2 3 4 3 2 5 – 2 3 4 3 2 5 -2 3 4 3 2 5 – 2 3 4 3 2 5 2.

About Valley Sleep Center:

Since 2002, Valley Sleep Center, accredited by the American Academy of Sleep Medicine, has provided Arizona with diagnostic sleep disorder testing in a home-like atmosphere, ensuring a comfortable, relaxing experience for patients.  Their Board Certified Sleep Medicine Specialists consist of experienced and knowledgeable physicians who provide expert advice across a multitude of sleep related disorders including insomnia, sleep apnea, snoring, excessive daytime sleepiness, hypertension, sleepwalking, and pediatric sleep problems.  They accept most insurance plans as well as Medicare.  For more information contact Lauri Leadley at 480-830-3900; https://valleysleepcenter.com.


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