The 5 Stages of Sleep Cycle

You must have heard that our mind never seems to stop working, even when we are sleeping. Have you wondered what our brain does when we are asleep? What is taking place inside our heads when we dream? Are we consciously aware of it? What takes place in our heads when we dream is still a topic of discussion in the field of psychology, but we do have a fair idea of what happens after we fall asleep. In this article, we will study about the sleep cycle.

The Sleep Cycle

After we fall asleep, we oscillate between the slow-wave and REM (Rapid Eye Movement) phases of sleep. Sometimes called the REM-NREM, sleep-dream cycle or the ultradian sleep cycle, it should not be confused with the circadian cycle- which is the alternation between sleep and wakeful state. The average sleep cycle in a human being lasts from 70 to 110 minutes, which means that when you sleep for 7-8 hours every night, you go through multiple sleep cycles. The stages can be broadly categorized into either REM or NREM. 

Brain waves

Before we move on to the actual phases of our sleep cycle, it is important to get an understanding of what brain waves are, and the kinds of brain waves. Messages in our brains are transmitted through electrical impulses; these rhythmic electrical impulses are known as brain waves. They can be measured using a device called EECG (electroencephalogram), which places electrodes on our skulls to capture these electrical impulses. There are beta waves, associated with alert wakeful states; alpha waves, associated with a calm and relaxed state of mind and delta waves, which are the slowest frequency waves, associated with deep sleep and unconsciousness. Contrasting to these are gamma waves, which are the highest frequency waves, associated with problem-solving and memory recall. 

Read more: Influence of Horror Movies on Sleep and Dreams

REM and NREM

But what is this REM and NREM that we keep referring to? REM stands for Rapid eye movement and NREM stands for Non Rapid eye movement. When someone is deep in sleep, try opening their eyelids; you will see their eyeballs moving around rapidly. This is, as the name suggests, what REM is. Non- REM phase is thus the period when you are relatively at rest when your brain activity is slower. This categorization holds all the phases of the sleep cycle, which are described below.

The 5 phases of our sleep cycle

1. Wakeful state- when you are awake, your brain waves can vary. We alternate between alpha, beta and gamma waves throughout the day, based on the task we are performing. 
2. Stage 1- this is when you are just about to fall asleep and are alternating between consciousness and unconsciousness. Your heartbeat slows down, your muscles start to relax and at this stage, you are producing alpha waves. It usually only lasts for a few minutes.
3. Stage 2- this is the period of light sleep lasting only for about 20-25 minutes, right before you fall into a deep sleep. Your body temperature drops in this stage. A characteristic feature of this stage is “sleep spindles”, which happen when brain waves spike up and down due to sudden electrical impulses. 
4. Stages 3 and 4- these are the deepest non-REM sleep phases that one experiences. It is during this stage that delta waves are present. The body at this stage is fully relaxed with no eye movement. Heartbeat and breathing are slowest, and the body is completely relaxed. This stage is very important because your body performs many health-promoting tasks, such as tissue repair, cell regeneration and building bone and muscle. You must sometimes feel groggy and find it difficult to adjust to your surroundings after being woken up. This is because your stages 3 and 4 have been disrupted, and you have been woken up suddenly after being in a very relaxed state.
5. REM Sleep- it is important to note that all the above stages were NREM. The fifth and last stage is the rapid eye movement sleep stage. It starts with being 10 minutes long, and then gradually becomes longer with each successive sleep cycle. This is the stage where we dream. This can be proved by analyzing the brain waves in this stage; they are beta waves. Breathing and eye movement become rapid; but the limbs become temporarily paralyzed, save for some twitching that may occur occasionally. 

Throughout our 7-8 hour sleep schedule, we go through multiple sleep cycles. They keep repeating, typically every 90 (20) minutes or so.

Read More: The Connection Between Sleep and Productivity

Disruptions to the sleep cycle

Altercations to our sleep cycle can be caused by a variety of reasons. Some are described below- 

• Sleep apnea– this is a sleep disorder where the person experiences shallow pauses in breathing. They experience pauses in breathing, followed by snoring and then a choking sound after which breathing is resumed. This causes the person’s sleep to be disrupted multiple times throughout the night, especially during Stage 4 and REM stage. Reduced time in these stages leads to them feeling drowsy throughout the day.  
• Narcolepsy– in this condition, you lose the ability to control your sleep and wake cycles. People often fall asleep in the daytime with brief, involuntary sleep episodes. You experience sudden muscle weakness coupled with an irresistible urge to fall asleep. It causes you to skip the initial stages and fall right into the REM stage. This limits the amount of sleep you get in the pre-REM stages, and thus you are not able to rest well. 
• Depression– it has been seen that depression causes the 3rd and 4th stages of sleep to become shorter, resulting in less time for the body to rest. The person thus feels tired constantly and unmotivated. Insomnia is also a common symptom of depression. 

Controlling sleep Alterations

It is very important to be well-rested. As seen above, getting a full sleep cycle helps to provide our body the rest that it needs after working all day, and also gives it time to replenish. We are also able to go through all the health-promoting tasks. You can practice the following methods to ensure that you get a good night’s sleep. 

• Practising meditation and deep-breathing exercises can help to put our minds at ease. If we are calm before bed, it is easier to fall asleep quickly without too many thoughts running through our minds. It slows down our breathing rate and our heartbeat, making it easier to slip into a deep sleep. 
• Make sure to switch off all the bright artificial lights well before bedtime. Exposure to such bright light may prevent the body from falling asleep. Use your bedside lamp or a reading light, but not bright artificial lights.
• Make sure to follow a set schedule for sleep. Don’t stay up too late and make sure you get enough sleep every night. Be consistent in when you go to sleep and when you wake up every day. It is advised to get 7-9 hours of sleep every night. 
• Avoid the intake of caffeine or alcohol right before you go to sleep. Having alcohol right before bed can increase the need to go to the bathroom in the middle of the night, and caffeine can make you excitable, preventing you from falling asleep. 
• Try doing some form of physical activity throughout the day. This will help exert you physically and make you tired enough to fall asleep quickly at night. 
• Put down your phone or other bright electronic items at least 30 minutes before bedtime. The artificial light from these can also be disruptive to your sleep cycle. 

Read More: 15 proven Tips for Better Sleep Hygiene

The article talks about the 5 stages of our sleep cycle- 4 stages of Non- Rapid Eye Movement and then the Rapid Eye Movement stage. We talked about brain waves- the electrical impulses through which the messages in our brain travel. There are multiple types of brain waves- alpha, gamma, beta and delta waves. The next section of the article discusses issues like narcolepsy and sleep apnea, which may cause alterations in sleep. It also talks about ways to make your sleep schedule better and to control these altercations.