This article is part of a series regarding the ‘basics’ you should know about your sleep. You can find the table of contents of this series here.

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When we think about sleep, we might instinctively think that our body and our mind are kind of shut down. But sleep is a little bit more complicated than that. When we sleep, we go through several successive stages that all have their particularity from a physical and mental point of view.

Let’s break down sleep together.

The royal way to study sleep is through an impressive device called Electroencephalogram (EEG). It tracks and records brain wave patterns thanks to electrodes that are attached to your head. The electrodes analyze the electrical impulses in the brain and send signals to a computer that records the results.

Thanks to this system, we can draw some characteristics about each sleep stage. The first thing that you will see is that there are two major stages of sleep that are very clearly distinguished by their waveforms; the REM stage (Rapid Eye Movement) where the brain is very active (low-amplitude, high-frequency waves, and alpha rhythm, as well as the eye movements for which it is named) and the non-REM stages where the brain is less active. 

By analyzing brain waves more deeply we might realize that sleep stages are even more complex than that. The NREM phase is divided into 4 stages (N1, N2, N3, N4) while the REM phase represents another stage (N5), for a total of 5 stages.

NREM Light sleep is composed of N1 and N2

NREM Deep sleep is composed of N3 and N4

REM sleep is composed of N5

Light sleep

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Light sleep is the stage in which sleep begins. It is also an intermediate phase between Deep sleep and REM sleep. It is precisely during this stage that the moment is most optimal to wake up and feel rested and alert. It is also during this stage that an individual is most sensitive to external factors, sensory stimulation such as noise, light or vibration.

The Circular ring knows precisely when the user is in a Light sleep stage since it corresponds to the stage with the most movements of the body and a heart rate close to normal, even if decreased.

Deep Sleep

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Deep sleep is one of the most essential sleep stages because it holds the secret of our performance and recovery. Deep sleep is responsible for energy restoration, growth, immunity and muscle repair. It is very difficult to be woken up at this time since the brain is much less sensitive to external stimuli. You really don’t want to wake up during that stage. Indeed, waking up during that stage is at the origin of this feeling of fatigue in the morning (called sleep inertia).

The Circular ring knows precisely when the user is in Deep sleep since the body moves only very little and the heartbeats are at their lowest and become regular.

REM sleep 

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REM sleep is the most famous sleep stage since it refers to dreams. It usually occurs at the end of the sleep cycle. It is considered very important because it is responsible for repairing the mind and consolidating the information you have learned during the day so that it can be stored in your long-term memory. It is also responsible for consolidating the memory of motor skills, daily gestures and stimulating your creativity. 

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The Circular ring knows precisely when the user is in REM sleep since there are fewer physical movements. This is thought to be a neurological barrier that prevents us from "acting out" our dreams) and the heart rate is very unstable, it often accelerates. 

Conclusion

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We understood that our sleep is comprised of cycles that are personal to us, that these cycles are comprised of several stages whose main categories are Light sleep, Deep sleep, and REM sleep and we understood their importance for our body restoration. 

That’s great! But what is the order of these different sleep stages, the patterns of our sleep cycle, how do we go from one cycle to another and in what proportions? Let’s discuss this in the next article of the series: The architecture of your sleep. Basics n°4 about sleep.