The 4 Stages of Sleep and What’s Happening Inside Your Brain

By Procera Health
November 05, 2023

Did you know, that a complete sleep cycle takes an average of 90 to 110 minutes and takes us through four distinct stages of sleep (although some people identify five stages with stages 3 and 4 characterized as deep sleep)? There are three stages of non-REM sleep and one stage of REM (rapid eye movement) sleep. We should go through a complete cycle of sleep between 4 and 6 times a night. However, not all sleep cycles are the same. The first 2 to 3 sleep cycles each night have relatively short REM sleep periods and long periods of deep sleep, but later in the night, REM periods lengthen and deep sleep time decreases.


Non-REM Sleep

About 75% of our sleep time is spent in non-REM sleep, with three phases:


Stage 1 — This phase, which typically last 5 to 15 minutes, is the stage of sleep when you are becoming drowsy and your muscle activity slows. You are slipping into sleep, but the sleep is still rather shallow. It is easy to be awakened in this rather dozy first phase of sleep.


Stage 2 — This also is a phase of light sleep, but your body is now preparing itself for deep sleep. Your body temperature drops and you begin to lose awareness of your surroundings.


Stage 3 — This is deep, Delta wave sleep. Delta waves are the lowest brain waves. It is difficult to rouse someone when they are in this stage of sleep. If someone were to awaken you during Stage 3 sleep, you’d probably feel confused and a little disoriented. During deep sleep your blood pressure drops, your breathing slows down, and your muscles relax.


REM Sleep

Stage 4 — REM Sleep: We spend 25% of our sleep time in REM sleep. 

This phase of sleep occurs typically about 70 to 90 minutes after you’ve fallen asleep, although some people enter REM sleep more quickly. During this period of sleep, your breathing becomes more irregular and shallow and your eyes will flit around in all directions. This is the stage of sleep when you dream. Your cerebral cortex gets involved during this period, inhibiting your body’s movements—essentially disabling your limbs—so you won’t act out your dreams. People who sleepwalk are said to have a weak or non-functioning neural command to disable these movements. The first period of REM lasts about 10 minutes. REM sleep will then recur about every 90 minutes, but subsequent phases of REM sleep will last longer, and the final stage, right before waking, can be as long as an hour. Just before awakening, your heart rate and breathing will quicken.


What Happens in the Brain During Different Phases of Sleep

The first and second stages of sleep are periods when your body gradually relaxes, disengages from the world, and acclimates itself to the sleeping state. Because these periods take only about 20 to 30 minutes to complete, this is generally thought to be the optimal length of time for cat naps or power naps, as the body will awaken from these stages in a refreshed, alert state, without any grogginess. When you nap longer than 30 minutes, there is a chance you will enter deep sleep. And waking from deep sleep can have the opposite effect you intend. 


A lot of regenerative work occurs during the deep stages of non-REM sleep. The body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. Deep sleep is a time when your energy stores are restocked and when you release and regulate various hormones. Two of these—ghrelin and leptin—play a role in balancing your appetite. When you don’t get enough sleep, you may feel the need to eat more the next day, which is why many people with chronic insomnia also struggle with weight issues.  


REM sleep is the phase of sleep when your brain is most active and intense dreaming occurs. In fact, certain brain regions become even more metabolically active during REM sleep than when you’re awake. The areas of the brain that regulate muscle movement, breathing and heart rate, all increase their metabolic rate. The limbic system, our emotion center, is also more active at this time. Interestingly, metabolism in the frontal cortex—the area of the brain that governs reason, decision-making and inhibition—goes way down, allowing the disinhibited limbic system to dominate. This is why our dreams are generally illogical, emotional, and nonsequential. 

It is believed that during REM sleep (as well as deep sleep) we form new memories and consolidate information from the previous day. In fact, studies have shown that if you teach an animal a task during the day and then disrupt its sleep that night, the new learning won’t be retained. This consolidation refers to emotional processing as well. When we experience a lot of REM sleep we are better able to consolidate emotional information from the previous day. It is important to also note that sleep is predominately a time when stress hormones decline and our fight or flight response is turned off. If we don’t get enough sleep, this decline in stress hormones doesn’t occur. In fact, stress and sleep lend new meaning to the term “vicious cycle.” Stress causes insomnia and insomnia causes stress.


Sleep is an essential part of our daily routine and is critical for maintaining good health. It is a restorative process that helps the body repair and rejuvenate itself. Getting enough sleep is important for cognitive health, energy, productivity, mood, and mental health. Which is why we developed Procera Sleep® — A natural sleep aid that helps you relax, fall asleep, and wake feeling refreshed. Procera Sleep contains 7 natural ingredients and vitamins that promote quality restorative sleep, facilitating a consistent nightly sleep cycle to help you replenish important neurotransmitters for optimal cognitive function and overall health. Click Here to get yours today!


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