From physical recovery to memory consolidation, many processes take place in the body and brain when we sleep. As you sleep, your brain goes through four separate stages of sleep, each with distinct patterns of activity and each with a key role in rest.


WHAT ARE SLEEP CYCLES


What are sleep cycles



What are the 4 stages of sleep


Step 1 - Non-REM sleep (does not involve rapid eye movement)

Step 2 - Non-REM sleep

Step 3 - Non-REM sleep

Step 4 - REM sleep



What is a sleep cycle


In addition to the amount of sleep, the quality of sleep is essential. Our ability to go through the various stages of sleep (and to spend enough time in the deepest) is what determines a quality sleep.


The stages of sleep make up a sleep cycle and each stage is important for good health and to ensure that we wake up feeling refreshed and well rested.



What are the 4 stages of sleep


In short, our brain goes through four different stages of sleep several times during the night.


There are four unique sleep stages - three that are classified as non-REM sleep (NREM), followed by the fourth stage, REM sleep.


Here's what researchers know so far about the four stages of sleep



Step 1 - Non-REM sleep (does not involve rapid eye movement)


At this stage, the sleep cycle begins, as we move from a waking state to a light sleep. This first stage is when we are just falling asleep. The heartbeat, eye movements and breathing slow down, the muscles relax, and the activity of the brain begins to decline.


Although it is easy to wake someone up in stage 1, they will quickly move on to stage 2 if they are not interrupted. In a typical sleep cycle, especially early at night, stage 1 sleep lasts only about 5 to 10 minutes at most.



Step 2 - Non-REM sleep


During stage 2 of non-REM sleep, our heart rate and breathing slow down even more as we move into a slightly deeper state of sleep.


This stage refers to the preparation for deep sleep and the following REM sleep. In general, body temperature drops, muscles relax completely, and brain waves slow down to small bursts of activity.


Experts say that electroencephalograms that monitor brain activity during sleep reveal what brainwave activity looks like at this stage. Sleep spindles (brain wave patterns) are triggered, indicating that NREM sleep is taking place. As the sensory nervous system (sight, hearing, taste, smell, and touch) stops during the day, sleep activity indicates that the brain is processing the memory of the day's events.


In this way, the brain turns short-term memories into long-term ones.


We spend most of our time in stage 2 sleep - about 50% of the night, for about 20 to 60 minutes per cycle.



Step 3 - Non-REM sleep


This final stage of non-REM sleep is classified as deep sleep on which the body relies to feel rested in the morning. At this stage, you are most disconnected from the waking state. Heartbeat and breathing slow down the most, as your body and muscles relax completely and it is most difficult to wake up during this time.


This is restful sleep, during which physical recovery and strengthening of the immune system takes place. Deep sleep refreshes the brain to encode new memories the next day.


Brain activity at this stage is marked by delta waves or slow-wave sleep. Because it is more difficult to wake up in this stage of deep sleep, if you are awake, you may feel more dizzy than you would have woken up in the other stages of sleep.


While memory consolidation takes place mostly During this stage of sleep, research suggests that at this stage, the brain consolidates memories, such as general knowledge, facts, or statistics.


We spend about 20 to 40 minutes in stage 3 of deep sleep on each sleep cycle.



Step 4 - REM sleep


The hallmark of REM sleep is in its name - the rapid movement of the eyes. In this fourth stage of sleep, the activity of the brain increases so much that it seems to be awake. Heart rate, blood pressure and respiration also increase again. The eyes move, but the muscles and the body do not.


Memory consolidation also occurs during REM sleep. The brain processes abstract thinking and emotional content. As the brain picks up on the day's events, it will look for emotional significance.


Researchers suspect that dreaming takes place in all stages of sleep, but that our most vivid, story-like dreams occur during REM sleep, because that is when emotional processing takes place. We usually remember our dreams at this stage, because it is the last one before waking up.


REM sleep is also responsible for processing the new motor skills that day. It seems that REM sleep is a way for the brain to cope with events that happened during waking up, to absorb new information that we have learned, and to process certain memories.


At the beginning of the night, REM sleep can last only a few minutes, but from the second half of it until dawn it can last up to an hour. In general, REM sleep accounts for about 25% of adult sleep.



Here's what to do to get better sleep



What is a healthy sleep cycle


A sleep cycle is when the brain goes through each of these stages of sleep during the night. In a sleep of up to eight hours, the body goes through about four to six sleep cycles.


Each sleep cycle usually lasts about 90 minutes, but can be extended to 120 minutes. The composition of a sleep cycle also changes during the night. During the first two cycles, people tend to spend more time in stage 3 of deep sleep, but in the second half of the night and in the morning, we may be mostly in REM sleep.


It is important to note that all stages of sleep are important, both deep sleep and REM sleep, which is crucial for learning and memory consolidation.


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