The Ups and Downs of Sleep Cycles

Our previous article spoke about the importance of it, how to find out if you’re getting enough of it, and most recently the link between sleep and mental health. This week I want to go back to basics - to take a look at what really happens under the bonnet when our eyes flutter closed each night. Surprisingly, when you pull back the curtains there’s so much more going on than most of us realise.

"The truth is, modern society has it backwards. Sleep is the single-most important tool in our arsenal for physical and mental recovery. Instead of making sleep fit into our busy schedules, we should be making our schedule fit around our sleep."

Sleep cycles are one of the automated processes that occur while we when we lay down for hours of sleep each night. Although you wake up feeling refreshed, your body has been repeatedly working through a series of these cycles with each one lasting between 90 and 110 minutes. Each cycle serves to forge connections in your brain, sorting your memories of the day just gone and filing them away, and ultimately helping you wake up feeling as fresh as a daisy.

The Stages

Within each cycle, there are two distinct stages after we fall asleep. Scientists in the 1950s noted that in the first stage sleeping patients’ eyes would - whilst closed - quickly dart side-to-side underneath the eyelids.

Researchers observed that this first stage, which has come to be known as Rapid Eye Movement (REM) sleep, was accompanied by active brainwaves in the sleeper. The brain is in fact so busy during REM that it is almost as active as that of a person who is awake! Periods of REM sleep are when we do our dreaming which is why it is often referred to as dream sleep.

The researchers also discovered there was a second, quieter and more peaceful stage following REM sleep. The patient's eyes stopped fidgeting and their brainwaves calmed to a gentle pace. The breathing and heart rate are slow and rhythmic, the blood pressure drops, and there is little movement from the sleeper.

This stage is known as Non-Rapid Eye Movement (NREM) sleep. NREM sleep can be further split into three phases. Each phase indicates how deeply a person is sleeping with NREM phase three being the deepest and the hardest to wake someone from.

REM Stage  – Brain waves highly active - as though the person is awake. Eyes rapidly move from side-to-side. Vivid dreams can occur. Muscle activity can be increased during this phase which can in turn increase sleep apnea symptoms.

NREM Phase 1 (Light) – The transition between wakefulness and sleep. Sleepers are easily awakened by external stimuli in their sleep environment whilst in this phase.

NREM Phase 2 (Light) – Body temperature decreases. Brain activity slows. The brain is also strengthening connections and storing memories during this phase.

NREM Phase 3 (Deep) – Slower brain waves during this phase. Sleepwalking or talking will occur during this phase. This sleep leaves you feeling the most refreshed. Delta waves occur here.

What does an average night look like? 

Each cycle of sleep sees you move from being awake, drifting into REM sleep, and then deeper into NREM phases one through to three before working back the other way. Once the cycle is complete, it begins again with five sleep cycles of 90 minutes to 110 minutes per night seen as typical - taking roughly seven to nine hours.

Cycles for the first half of the night are dominated by periods of NREM phase three and a brief amount of time in REM. As the cycles progress, the time in NREM shortens and the amount of time spent in REM increases, with the longest periods of REM toward the end of the night. NREM singles out and removes neural connections that aren’t needed, and leaves you feeling refreshed. REM strengthens neural connections and aids the preservation of memory.

This incredible, finely tuned process has been occurring in human brains for thousands of years. We close our eyes and our incredible brain takes over. Cutting our sleep short - whether by choice or due to sleep problems like insomnia or restless leg syndrome - lack of sleep means our brain misses out on the opportunity to complete the cycle.

The truth is, modern society has it backwards. Sleep is the single-most important tool in our arsenal for physical and mental recovery. Instead of making our rest fit into our busy schedules, we should be making our schedule fit around our sleep.

Changing our lifestyles to support our circadian rhythm. Improving our bedtime habits so we don't feel tired during the day, and that help staying asleep at night. So next time you’re worrying about your busy week, remember to make space for sleep in your life.

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