Sleeping represents a third of our life and is pivotal to our health. The act itself can be described as a state of body relaxation where brain-wave activity changes with the nervous system becoming less reactive to external stimuli. If you decide to look more closely there is actually a lot that happens. Our sleep behaviour varies considerably as our bodies do different things at different times to allow us to recuperate. A night of sleep consists of 4 different cycles that follow each other 3 to 6 times! These 4 cycles incorporate 2 light sleep stages and 2 deep stages.

Here’s a description of these stages and what happens while we’re in them.

boy sleeping

Stage 1: Initial Light Sleep

This is when you’re in the act of falling asleep. Polysomnography shows a 50% reduction in activity between wakefulness and stage 1. As you fall into Morpheus’s arms your awareness and heart rate gradually decreases. Your brain can still process surrounding information and remains sensitive to external stimuli: a light being switched or hearing your name is enough to wake you. In other words you’re not completely asleep but you’re on your way. This stage is the most expedite, usually lasting 5 to 10 minutes.

Stage 2: Intermediate Light Sleep

This is basically the same as above but in a deeper state. It will be harder to wake you. Polysomnographic readings show intermittent peaks combined with softer waves in muscular movements indicating spontaneous periods of muscle tone mixed with periods of muscle relaxation. Body temperature and heart rate decrease as the body prepares to enter deep sleep. This stage is the biggest, representing about 50% of total sleep.

Stage 3: Slow Wave Sleep

Slow Wave Sleep (SWS) is when the magic happens. Representing roughly 25% of our total sleep, this phase (sometimes divided into two stages by experts) is characterized by electromyogram records of slow waves of high amplitude, indicating a pattern of deep sleep and rhythmic continuity. It is the deepest and most restful sleeping period that allows for full body restoration. During this time our brain cells rewire themselves, process and retain information learned through the day, make new connections or conversely break them. The exact nature and role of SWS is quite mysterious and there’s still much to learn about its initiation and physiological functions. Being awakened during SWS is rough and often results in feeling wobbly and irritable for the rest of the day.

Stage 4: Rapid Eye Movement Sleep

Rapid eye movement sleep is the phase when another form of magic occurs: dreaming. Once our bodies are restored from SWS we enter REM. In French this phase is also called paradoxical sleep because it presents both symptoms of deep and light sleep at once: our brain, heart rate, and ocular activity operates at high levels yet our body is paralyzed with muscles completely relaxed and atonic. It is thought that this muscle paralysis is meant to keep the body from acting out the dreams that occur during this intensely cerebral stage. This is the phase during which we elaborate our longest and most vivid dreams with on average 4 to 6 dreams a night (with 80% of them falling into oblivion). Representing about 25% of our total sleep, a higher proportion of REM phases take place in the second half of our sleep whereas SWS has a higher proportion occurring during the first half. The first period of REM typically lasts 10 minutes, with each recurring REM stage lengthening, and the final one lasting an hour (your recalled morning dreams).

girl asleep on book

Let us know if you enjoyed this post and would like to know more about sleep! 🙂

Pin It on Pinterest