What are the stages of sleep?

Stage 1

Also known as N1, this is when we can easily drift in and out of sleep. We are easily woken from this stage, it only lasts for around 5 minutes and contributes to approximately 5% of the overall sleep cycle. This phase is also characterised by eye movements that, unlike REM, occur more slowly.

Stage 2

The N2 stage of sleep is truly fascinating as the brain waves become low in amplitude and high in frequency which shields the brain from external noises - this type of brain wave is called a sleep spindle. This is when the body is preparing itself for deeper sleep - the body temperature will drop and our brains will use this time to process memories. 50% of the sleep cycle is taken up by this N2 stage.

Stage 3

In this stage of deep sleep, blood is redirected from the brain to the muscles, allowing them to receive oxygen and nutrients which is essential for muscle repair and growth. If you are woken from N3 sleep, you’ll feel very groggy and find mental tasks difficult. The idea that deep sleep is the most important stage of sleep is simply wrong, and you should disregard it - all stages of sleep are equally important. Deep sleep is said to be the most restorative sleep phase and is crucial for repair and growth. Deep sleep occurs in longer periods during the first third of the night with adults spending about 10-20% of total sleep time in deep sleep². However, the assumption that deep sleep alone determines how long we should sleep is also wrong.

Stage 4

REM sleep is perhaps one of the most interesting subtopics of sleep as the brain becomes even more active than when we are awake, which is why this stage is called a paradoxical sleep. REM usually starts about 90 minutes after falling asleep, and this is when you’ll start experiencing vivid dreams. As the muscles in the body are also asleep, you are unable to somewhat ‘act out’ your dreams in movement.

Why are stages of sleep important?

Both REM and non REM stages of sleep have benefits to both the physical and mental aspects of the human body, therefore neither is more important than the other.

• N2 sleep is important for memory refreshment, so we wake up the next day with the ability to learn new information. That’s why it’s crucial to get a good night's sleep before an exam or important learning event.
• N2 and N3 both contribute to memory consolidation which effectively means that sleeping after learning will enhance your memory.

• REM sleep plays a highly important role for our mental health: during REM sleep, concentrations of the stress-related, anxiety-triggering chemical noradrenaline are shut off within the brain – simultaneously, emotion and memory related structures (i.e. amygdala and hippocampus) of the brain are reactivated during REM sleep. This enables the re-processing of upsetting memories in a stress-free state.