Experts believed that sleep was a passive state, wherein your body and brain shut down for the night to rest and recover. But now, researchers have found out that sleep is a highly active time, a period during which your brain and some physiological processes are at work.
You usually go through 4-5 sleep cycle stages that begin with light NREM sleep and end in REM sleep, with each cycle taking between 70 and 120 minutes to complete. These stages are responsible for your memory consolidation, processing what you have learned the day before, and other essential cognitive functions.
A sleep sound machine can help you create a sleep-friendly environment for a more restorative and uninterrupted sleep. When your sleep is interrupted, you can wake up feeling groggy and drained, no matter how many hours you slept.
When you sleep, you undergo two different stages: NREM sleep and REM sleep. Non-REM (NREM) sleep is divided into three stages, distinguished from each other and from wakefulness by characteristic patterns of brain waves.
Whereas, rapid eye movement (REM) sleep is the darting movements of your eyes under closed eyelids. Brain waves during REM sleep are very similar to the brain waves during wakefulness.
The first three stages of your sleep are NREM sleep, while the fourth and final stage of sleep is REM sleep.
What Happens in the Three Stages of NREM Sleep
The first stage of NREM sleep is known as stage 1 sleep. This stage is where you transition from wakefulness to sleep. During this stage, there is a slowdown in both the rate of your heartbeat and respiration. Moreover, this stage also involves a decrease in both overall muscle tension and core body temperature.
In terms of brain wave activity, stage 1 sleep is associated with both alpha and theta waves. In its early stage, it produces alpha waves, which are relatively low-frequency, with 8-13 Hz, high-amplitude patterns of electrical activity that become synchronized. This activity of the brain wave is similar when you are very relaxed, yet awake. As you continue through stage 1 sleep, there is an increase in theta wave activity. These waves have a lower frequency, ranging from 4-7 Hz, and higher amplitude brain waves than alpha waves. It is easy to wake you up in stage 1 sleep. In fact, many individuals often report that they have not been asleep if they are awoken during stage 1 sleep.
In stage 2 sleep, your body goes into a state of deep relaxation. Theta waves are still dominant in the brain activity, but they are interrupted by brief bursts of activity known as sleep spindles. These are rapid bursts of higher frequency brain waves that may be vital in your memory and learning. Moreover, associated with stage 2 sleep is the appearance of K-complexes. These are very high-amplitude patterns of brain activity that may occur in some cases in response to environmental stimuli. K-complexes might serve as the connection to higher levels of arousal in response to what is going on in your environment.
Stage 3 sleep is often referred to as slow-wave sleep or deep sleep, as these stages are characterized by low frequency, with less than 3 Hz, and high amplitude delta waves. During this stage, your heart rate and respiration become significantly slowed. It is much more difficult to wake you up from sleep during this stage than in earlier stages. However, individuals who have increased levels of alpha brain wave activity during this stage said that they do not feel refreshed upon waking despite sleeping for hours.
The Importance and Uniqueness of REM Sleep
REM sleep is characterized by rapid movements of the eyes. The brain waves linked with this stage of sleep are very similar to those observed when you are awake, and this period is where dreaming occurs. This stage is also associated with paralysis of muscle systems in your body, except those that make respiration and circulation possible.
Thus, there is no movement of voluntary muscles during REM sleep. In fact, REM sleep is often referred to as paradoxical sleep due to the combination of high brain activity and lack of muscle tone. Similar to NREM sleep, REM has also been linked to various aspects of memory and learning.
If you are deprived of REM sleep and then sleep without any interruption, you will more likely spend more time in REM sleep to make up for the lost time in this stage. This is known as the REM rebound, and it suggests that REM sleep is also homeostatically regulated.
The Typical Progression of Sleep Cycles Throughout the Night
Throughout your time asleep, your brain cycles repeatedly through non-REM and REM sleep. On average, you go through 4-6 sleep cycles per night and spend 90 minutes in each sleep cycle stage. Here’s how it usually progresses:
Stage 1
Stage 1 begins when you shift from wakefulness to sleep. This stage is a period of light non-REM sleep that slows down your heart rate, eye movements, and breathing. Your muscles also relax, although they may twitch occasionally. Stage 1 sleep is brief and only lasts for around 1-5 minutes.
Stage 2
In this stage, deeper non-REM sleep occurs, where your muscles relax further, your eye movements stop, and your body temperature drops. This stage lasts for around 25 minutes, lengthening with each new sleep cycle. Overall, this stage accounts for more than 50% of sleep in adults.
Stage 3
Stage 3 is the deepest stage of the sleep cycle and the hardest to awaken from. During this stage, your heart rate and brain waves become regular. You will experience the deepest sleep during the first half of the night. If you wake up from this stage, you may feel mentally foggy for around 30-60 minutes.
Stage 4 (REM Sleep)
The last stage of the sleep cycle is REM sleep. During this stage, your eyes move quickly and rapidly from side to side, and your breathing quickens and becomes more erratic. As mentioned above, this is the stage where dreaming occurs. REM sleep lasts for approximately 10 minutes during the first sleep cycle. In the final cycle of your sleep, it can last up to 1 hour.
How Your Sleep Cycles Change with Age
As you grow older, your sleep pattern changes, which is also known as sleep architecture.
Your sleep follows a pattern between different stages of sleep: from light sleep to deep sleep and into REM sleep. Each stage has a vital role in your physical and mental health. REM sleep is essential for your memory and cognition, whereas deep sleep is important for storing memories and repairing damaged cells or tissues within your body.
Growing older means more light sleep and less deep sleep. When you’re in a light sleep, you are more prone to waking in the middle of the night, leading to daytime exhaustion.
Two key systems control your sleep: homeostasis and your body clock or circadian rhythm, which are influenced by certain hormones in your body, and these changes in the release of these sleep-related hormones that is evolving your sleep architecture as you age.
What Happens When Your Sleep Cycles Are Interrupted
As an adult, it is recommended to get 7-9 hours of sleep each night. Waking up once or twice is normal; however, waking up from prolonged periods at least four times throughout your sleep is not normal. When your sleep cycle is interrupted, your body has to reset and start going through the stages all over again, which could prevent you from getting deep and restorative sleep.
Side effects of Interrupted sleep cycles:
- Daytime sleepiness
- Irritability
- Decreased creativity and accuracy
- Increased stress
- Tremors, aches, and memory lapses or loss
Simple Ways to Improve the Quality of Your Sleep Cycles
Here are simple ways you can improve the quality of your sleep cycles for a more restorative sleep.
Consider a supplement: Taking a supplement can help reduce the time it takes for you to fall asleep as well as promoting a deep and refreshing sleep.
Establishing a consistent bedtime routine: Insufficient or irregular sleep over a few days can result in abnormal sleep cycles
Improving your sleep hygiene: Along with having a consistent bedtime routine, you can also create a relaxing nighttime routine and practice sleep meditation.
Avoiding alcohol in the evening: Avoid alcohol, and food and drinks in general as you get closer to bedtime. Otherwise, you’ll miss out on REM sleep early in the night and then get too much of it later on.