As you slumber, you cycle through different stages of sleep that each have specific patterns of brain activity and unique benefits to your overall health and wellbeing.
What Exactly are Sleep Stages?
There are four distinct sleep stages and each is defined by factors such as brain activity, heart rate, eye movement, body temperature, and health benefits.
Sleep stages can be broadly segmented into two types:
Non-Rapid Eye Movement (NREM) sleep:
The first sleep stages made up of N1, N2, and N3.
Rapid Eye Movement (REM) sleep:
The last stage of sleep made up of REM sleep.
Your body will travel through each of these stages of sleep to complete one sleep cycle. During a typical night, you’ll go through four to five sleep cycles which last from 90 to 120 minutes each. The overall pattern of sleep during a particular night is known as your sleep architecture; if you use a wearable device or completed a sleep study, you may have already seen this mapped out.
Sleep stages can vary between individuals and on a nightly basis due to factors such as age, sleep patterns, health, activity levels, and substance use. For instance, on days you exercise intensely, you’re likely to get more deep sleep.
NREM Stage 1/N1 Sleep
This stage is your briefest and lightest stage of sleep and typically occurs during the transition from wakefulness to sleep when you’re dozing off. It lasts approximately 1-10 minutes, and you can be easily awakened from this stage of sleep. A person will generally only revisit this stage again during the night if they wake up and go back to sleep.
N1 sleep is characterized by:
• Alpha and theta brain waves — indicative of a relaxed mind
• Regular muscle tone that begins to relax
• Regular breathing
• Slow, rolling eye movements
Health Benefits of N1
This stage is important for transitioning your brain and body into N2 and subsequent sleep stages.
NREM Stage 2/ N2 Sleep
After N1 your body moves into the next stage of sleep known as N2, which is a lighter sleep that makes up the majority of the night. It lasts approximately 30-60 minutes, and you can be awakened from this stage of sleep but not as easily as in N1. Each N2 stage usually becomes longer as the night progresses, leading to about 50% your overall sleep time spent in this stage.
N2 sleep is characterized by:
• Sleep spindles — bursts of synchronized brain activity occurring in rhythmic waves
• K-complexes — long delta brain waves
• A drop in body temperature
• Slower heart rate and breathing
• No eye movements
• Teeth grinding (bruxism) occurs during this stage
Health Benefits of N2
Numerous studies have shown that sleep spindles occurring during this stage are important for memory consolidation, helping to store information in your long-term memory. K-complexes are believed to help promote sleep in the presence of sleep disruptions, such as noise, and may also help with memory consolidation. This stage is also important for transitioning your body into the most restorative stage of sleep.
NREM Stage 3/N3 Sleep
N3 is where your body becomes fully relaxed into the deepest stage of sleep. It lasts approximately 20-40 minutes, and it is very difficult to be awakened during this stage. If awakened during N3, you’re likely going to feel very groggy. The majority of your N3 sleep occurs during the first half of the night and gets shorter with each recurring sleep cycle. This deep sleep stage makes up approximately 5-15% of your total sleep time.
N3 is characterized by:
• Increase in delta waves — associated with the highest levels of relaxation
• Heart rate and breathing are at their slowest rate
• Blood pressure drops
• No eye movements occur
• Muscles relax and are unlikely to show movement
• Secretion of hormones, like human growth hormone, from the pituitary gland
• Increased glucose metabolism in the brain
Health Benefits of N3
This deep sleep stage is associated with an array of health benefits, such as:
• Increased tissue repair and cell regeneration
• Muscle growth and bone repair and remodeling
• Fat metabolism
• Strengthening of the immune system
• Short-term and long-term memory
• Processing information learned during the day
• Clearing cellular waste from the brain
• Optimizing and preparing brain synapses for the next day to help improve learning and cognition
REM Stage R Sleep
REM sleep is when your brain becomes active, nearing levels similar to when you’re awake, but your body experiences temporary paralysis of the muscles, known as atonia. It lasts 10-60 minutes and it is difficult to be awakened from REM sleep, although spontaneous awakenings may occur. You generally don’t enter REM sleep until you’ve been asleep for 90 minutes. The length of REM stages increases as the night progresses, with the first REM lasting only a few minutes and later stages lasting up to an hour. REM sleep makes up about 25% of your total sleep time.
REM is characterized by:
• Beta and gamma waves which are similar to wakefulness
• Rapid eye movements
• Muscles become paralyzed (except for eye and breathing muscles), but twitches may occur
• Most vivid dreams occur
• Increased oxygen use in brain
• Variable heart rate and blood pressure
• Increased levels of acetylcholine
• Brain metabolism increased by up to 20%
Health Benefits of REM
REM sleep is believed to be important for cognitive functions such as learning, memory, creativity, problem-solving and emotional processing. Many people will experience an increase in REM sleep after periods of learning, suggesting it plays a very important role in memory consolidation. There is some evidence that REM is important for your stress response and may provide protection from daily stressors.
How can I Improve my Sleep Architecture?
Practicing good sleep hygiene like keeping a regular wake time, avoiding blue light within 2-3 hours of bedtime, and practicing daily mental decompression can all help to boost your sleep architecture. You can also improve sleep stability by listening to pink noise during the night, ensuring your room is dark (or wearing a sleep mask), and exercising during the day.
