The Ups and Downs of Sleep Cycles

Our previous article spoke about the importance of sleep, 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 sleep. Although you wake up feeling refreshed, your body has been repeatedly working through a series of these sleep 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 of Sleep

Within each sleep cycle, there are two distinct stages of sleep. 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 sleep 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 sleep 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 sleep and the hardest to wake someone from.

REM Sleep – Brain waves highly active - as though the person is awake. Eyes rapidly move from side-to-side. Vivid dreams can occur.

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

NREM Phase 2 (Light Sleep) – Body temperature decreases. The brain is strengthening connections and storing memories.

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

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 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 sleep. As the cycles progress, the time in NREM sleep shortens and the amount of time spent in REM increases, with the longest periods of REM toward the end of the night. NREM sleep singles out and removes neural connections that aren’t needed, and leaves you feeling refreshed. REM sleep 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 by accident, 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 sleep fit into our busy schedules, we should be making our schedule fit around our sleep. So next time you’re worrying about your busy week, remember to make space for sleep in your life.