THE SCIENCE BEHIND SLEEP

AND THE SLEEP CYCLE

Firstly, why do we sleep?

We spend approximately one-third of our lives sleeping, yet sleep is still something that scientists know relatively little about. What we do know, is that sleep is essential to the maintenance of physical and psychological health. A function that allows the body and mind to recharge leaving us refreshed and alert when we wake up.  Whilst poor sleep can leave us with memory issues, mood changes, weakened immunity as well as many other side effects.

All sleep is not the same

Throughout our time asleep, our brain will cycle repeatedly through two different types of sleep: REM (rapid-eye movement) sleep and non-REM sleep. Unlike non-Rem sleep, during REM sleep, our eyes move around rapidly in a range of directions, but don’t send any visual information to the brain. The sleep cycle is broken down into 4 stages, one for REM sleep and three that form non-REM (NREM) sleep.  These stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterize each stage.

4
Stages of Sleep

Understanding The Sleep Cycle

A sleep cycle consists of 4 stages with a typical sleep cycle lasting for around 90 minutes.  On average a typical night’s sleep should consist of about 5-6 full sleep cycles
Stage 1, (1-7 minutes)
  • Very light sleep, can be woken easily
  • Heartbeat and breathing slows, eye movements slow down
  • Muscles relax
  • Brainwaves begin to slow down
Stage 2, (10-25 minutes)
  • Light sleep
  • Heartbeat and breathing slows more
  • Body temp drops
  • Muscles relax further
Stage 3, (20-40 minutes)
  • Deep sleep, difficult to wake
  • Heartbeat and breathing slows to their lowest levels
  • Muscles stay relaxed
  • Brainwaves slow down still further
Stage 4, (20-40 minutes)
  • REM sleep
  • Eyes move rapidly side to side
  • Breathing speeds up and can become irregular
  • Heartrate increases
  • Blood pressure increases

The Sleep Cycle Stages Explained....

Stage 1

The first stage of sleep, known as light stage sleep, is one of the shortest, lasting one to seven minutes. In this stage, the mind and body begin to ‘slow down,’ causing us to feel drowsy and relaxed. During this phase we can still be woken easily.

HELPFUL TIP:

If you want to take a power nap, make sure it isn’t more than twenty minutes so you don’t enter deep sleep, (stage 3). Taking too long a nap means you may wake up during deep sleep, which leads to sleep inertia where you feel groggy. If you want a longer nap, try to aim for 90 minutes or more so you make it through an entire cycle.

Stage 2

In the second stage of sleep, still referred to as light sleep, eye movement, brain waves, and muscle activity start to decrease and prepare the mind for deep sleep. During this stage, the brain produces sudden spikes in brain waves known as sleep spindles for their spindly appearance on EEG charts. These spikes in brain activity are thought to play a role in long term memory consolidation and sensory processing, making this an important stage as we age. It is believed that it is during this stage that most of our memories are formed

Stage 3

During the third stage of sleep we enter into a deep sleep. Our muscles become fully relaxed or ‘limp’ in this stage, and our breathing rate, blood pressure, and body temperature all decrease significantly. The body produces growth hormones, regulates immune system function, and develops and repairs muscle tissue during this stage, making it critical for physical health and recovery

Stage 4

This is the only stage of REM sleep. During this time, brain activity picks up significantly, and most of the body — except the eyes and breathing muscles — experience temporary paralysis. Although dreams can happen during any stage, the most intense dreaming takes place during REM sleep.

The REM sleep stage is believed to be enabling key functions like memory and learning. As the night goes on, it’s normal to spend a greater percentage of time in REM sleep with most of it occurring in the second half of the night.

As we age, however, the timing and duration of our sleep cycles change. Older individuals tend to experience a much longer sleep cycle with less time in REM, as opposed to infants who experience shorter cycles with more REM sleep.

 

HELPFUL TIP:

Avoid substances like caffeine and alcohol too close to bedtime as these can disrupt your sleep cycles. For example, caffeine ingested too close to bed can not only make it more difficult to get to sleep but also can have a negative effect on your deep sleep in the first half of the night.

Alcohol, on the other hand, tends to ruin the second half of your night’s sleep. If you drink before bed, about halfway through the night, your body will start processing the alcohol, and it begins to act as a stimulant.

FAQ

What is a sleep cycle?

Throughout our time asleep, our brain will cycle repeatedly through two different types of sleep: REM (rapid-eye movement) sleep and non-REM sleep. Unlike non-Rem sleep, during REM sleep, our eyes move around rapidly in a range of directions, but don’t send any visual information to the brain. The sleep cycle is broken down into 4 stages – a typical night’s sleep consists of about 5-6 full sleep cycles.

Why does the sleep cycle matter?

Sleep stages are important because they allow the brain and body to recuperate and develop. Failure to obtain enough of both deep sleep and REM sleep may explain some of the profound consequences of insufficient sleep on thinking, emotions, and physical health.

Sleepers who are frequently awoken during earlier stages, such as people with sleep apnea, may struggle to properly cycle into these deeper sleep stages. People with insomnia may not get enough total sleep to accumulate the needed time in each stage.

How long is a sleep cycle?

The average sleep cycle lasts about 90 minutes.

How many sleep cycles should you get each night?

A typical night’s sleep consists of about 5-6 full sleep cycles. However, each sleep cycle is different.  You will spend longer in the non-REM sleep stages during the earlier cycles and by the last 2-3 cycles you will spend more time in REM sleep and stage one, which is the lightest part of your sleep.

How can you improve your sleep cycle?

While you don’t have full control of your sleep cycle, you can take steps to improve your chances of having a healthy progression through each sleep stage.

A key step is to focus on improving your sleep hygiene, which refers to your sleep environment, lifestyle and sleep-related habits.  Achieving a more consistent sleep schedule, avoiding alcohol before bedtime, and eliminating noise and light disruptions can help you get uninterrupted sleep and promote proper alignment of your circadian rhythm.

What time should I set my alarm for?

You should try to time your alarm to go off during your lightest sleeping period and avoid waking up when you are in the later stages of the sleep cycle and your deepest sleep. Each sleep cycle last approximately 90 minutes and you should aim to get 6 full sleep cycles if possible. This means aiming for 9 hours of uninterrupted sleep.  If you cannot fit in 9 hours of sleep, it would then be best to aim for 5 complete sleep cycles i.e. 7.5 hours of sleep to avoid waking up mid cycle and feeling groggy.