What is sleep? Well, it needs no explanation because we experience it every day. But to put it down to words as per the Cambridge dictionary it is – the resting state in which the body is not active and the mind is unconscious.
A lot of research has gone into sleep and its various stages, simply because it’s something where much happens in the body, such as repair, regeneration, memory consolidation and so on. So to better understand this vital state of rest, let’s take a look at the different stages of sleep.
Sleep is categorised into NON-REM and REM sleep.
- REM stands for Rapid Eye Movement. REM refers to the quick movements that happen in the eye during the deeper and latter times of sleep.
- During Non-REM sleep, there are no eye movements. This is also known as NREM, and referred to as the earlier part of the sleeping. Non-REM is further divided into three parts. After these three stages, the REM stage occurs.
All of these stages form one sleep cycle. There may be several cycles in one night. Each cycle may last for around 90 minutes.
Different Stages Of Sleep
This is closest to you being awake; it happens a few minutes into slumber, and is easy to be woken up during this stage. Often at stage 1, people are woken by a sudden feeling of falling. Muscle activity and heart rate slow down and brain waves decrease in frequency. Brain waves move from high frequency (beta and gamma) to slower frequency (alpha). One is still aware of the environment to some extent. Stage 1 sleep usually lasts for approximately 10 minutes.
This is a dreamless stage, but not a deep sleep. There are no eye movements, muscle activity stops, heart rate slows down, brain waves also slow down further, but there are intermittent peaks, called as sleep spindles. This brain activity is important for information processing. The body is not able to respond to outside stimuli. The body spends maximum time in stage 2 sleep during the night.
This is the stage of deep sleep. Breathing and heart rate are at the lowest. There is no eye movement. It is very difficult to wake up a person in this stage, and if they are woken up, they would feel cranky and would need time to get back to a normal woken up state. Repair and growth of tissues, muscles take place. With age, the amount of stage 3 sleep goes down. It is is a combination of two stages (that is 3 & 4). During stage 4 sleep, delta waves (low frequency) are created. They are important for healing and regrowth.
It happens at the end of each sleep cycle. REM sleep is shortest in the first sleep cycle of the night. As the name suggests, there are rapid eye movements. There are also high frequency brain waves and a lot of brain activity at this stage. The body is almost in a paralyzed state. You dream in this stage. This time is important for the ability to learn and for memory consolidation, meaning fixing or stabilising a memory after you have encountered it. Kids spend more time of their slumber in this stage than adults.
A Few Points To Note
- The time spent sleeping that a person requires differs with age. Children on an average require 10-15 hours, because the different sleep stages are required to carry out essential tasks. However, adults need 7-8 hours of sleep.
- Caffeine, alcohol, tobacco, and medicines can affect the REM stage.
- Additionally, even an alarm can spoil your normal body rhythm if it’s waking you up in your REM cycle. You will get up being groggy, dull and irritated during the day.
Many people have conducted extensive research in the subject of sleep, why we need it, and what are the stages. These studies are critical because sleeping is not simply a dormant state as was thought so earlier. It is a state when most important physiological and brain-related activities happen, without our conscious effort.