When reaching the end of the day and are off to a good night's sleep, our brains and bodies don't just shut down for the night when we hit the pillow. Far from it, the body enters essential repair and restoration work.
A significant part of the activity occurs during the Rapid Eye Movement (REM) sleep cycle. REM sleep is when we dream, and our brain activity is similar to when we’re awake. Around 25% of our total sleep time is spent in the REM stage, with the first REM cycle of the night being the shortest. The other 75% of our sleep time is spent in the other sleep categories known as non-REM sleep. Understanding the different sleep phases helps us realise the importance of sleep for all aspects of our lives and why we should aim to get the recommended hours of good-quality sleep.
Understanding REM Sleep
REM sleep was discovered by scientists studying sleeping infants. They noticed their eyes moved rapidly from side to side, which gave the name to the last sleep cycle (rapid eye movement sleep - REM sleep).
During REM sleep, the eyes move rapidly behind closed eyelids, the heart rate speeds up, and the brain waves slow down, but the brain is highly active. There is also a complete loss of muscle tone, unlike during non-REM sleep, where there is partial muscle tone. People are woken more easily during REM sleep than during non-REM sleep cycles.
During a typical night, a person will go through multiple cycles of REM sleep. The first REM sleep stage doesn't occur during the first 90 minutes of sleep and only lasts a few minutes, while the last REM cycle may be as long as one hour. The REM stages account for approximately 25% of an adult's sleep time every night.
The Functions of REM Sleep
REM sleep cycles are important in various aspects of health and well-being, including cognitive functions such as memory, learning, emotional processing, and creativity.
Young babies spend most of their early lives in REM sleep. As the child grows and the brain develops, REM sleep reduces until it stabilises during adulthood. And then later in life, REM sleep levels reduce.
The most vivid and unusual dreams occur during REM sleep, while dreams are less common during non-REM cycles. In a REM sleep and dreaming study, volunteers who were woken up during their REM sleep could recall elaborate, hallucinogenic, and emotional dreams. The volunteers who were woken up during non-REM sleep reported fewer, less vivid, or emotion-laden dreams. Emotional processing occurs during the REM stage of sleep. The part of the brain that processes emotions, the amygdala, is activated during this time. The brain is also busy processing new learnings and motor skills from the day, saving some to memory and deleting others.
Large amounts of REM sleep after a traumatic event can help with recovery and possibly reduce the chance of developing post-traumatic stress disorder. The REM rebound effect occurs when a person receives more REM sleep than regularly following a period of sleep deprivation, a stressful time, or starting or ceasing some medications or recreational drugs.
REM vs Non-REM Sleep: The Basics of Sleep Cycles
There are four cycles of sleep - two stages of light sleep (non-REM), one of deep sleep (non-REM), and REM sleep. A new sleep cycle starts every 80 to 100 minutes, where slightly waking up between the cycles is common. Stage 1 is the shortest - up to 7 minutes long - followed by stage 2, which lasts between 10 and 25 minutes, then stage 3, 20 to 40 minutes long, and stage 4, 10 to 60 minutes.
Most adults will experience four to six sleep cycles per night, with stage one not repeating. The deep sleep cycle is longest early in the night and much shorter in the early hours of the morning, while the REM cycles increase in length with each sleep cycle. Adults need around two hours of REM sleep each night. So, people who don’t get the recommended 7-8 hours of sleep per night are unlikely to get enough REM sleep.
During non-REM sleep, there is a significant reduction in blood flow and metabolism.
Stage 1 of Light Sleep (N1)
During the falling asleep stage, the brain slows down, but breathing is regular, and the body has some muscle tone as it's not yet fully relaxed.
Stage 2 of Light Sleep (N2)
The heart rate and body temperature decrease as the body transitions into deep sleep.
Stage 3 Deep Sleep (N3)
During this stage of sleep, the brain waves are at their slowest. People are less likely to be woken up while the body repairs itself, restoring bone, muscle, and tissue and boosting the immune system.
REM Sleep: Stage 4
REM sleep is the most important stage of sleep and comes at the end of the cycle. During REM sleep, the blood flow and metabolism are similar to wakefulness. In the emotions section of the brain, blood flow is even higher than during the day while the brain is busy dreaming and processing.
People who wake up feeling groggy and struggling to concentrate may not be getting enough REM sleep. Adversely, people getting the recommended hours of sleep are more likely to get enough REM sleep and consequently tend to feel refreshed - mentally and physically.
Factors Influencing REM Sleep
Almost half of the Australian adult population report having at least two sleep issues. On one hand, some people don’t get the recommended hours of sleep, while others sleep longer than recommended. Some complain of poor sleep quality, while others have a diagnosed sleep disorder such as insomnia, restless leg syndrome, or obstructive sleep apnoea.
There are a range of factors that influence REM sleep quality. Some include lifestyle choices that can be improved, while other factors, such as age and genetics, can’t be changed. People with insomnia usually get less REM sleep. Antidepressant medication can suppress REM sleep. Sleep apnea interrupts sleep, so people with obstructive disorder don’t achieve REM sleep quality, causing them to feel groggy during the day (even with enough hours of sleep). Treating sleep disorders can improve the quality and quantity of REM sleep.
Drinking alcohol can delay the onset of the first REM sleep and cause you to have too little time spent in REM sleep, and tobacco can also interfere with sleep cycle progression. The elderly often have shorter nighttime sleep, which means less REM sleep and more time in non-REM sleep, particularly stages 1 and 2 of light sleep.
Poor sleep can impact a range of body functions - from regulating appetite, metabolism, and hormone and cardiovascular function.
Improving REM Sleep
The first step to improving REM sleep is understanding how crucial it is for a healthy and happy life. Try the following tips:
- Go to bed and wake up at roughly the same time each day. Going to bed late and sleeping in during the weekends can play havoc with your body’s circadian clock.
- Sleep in a cool, dark bedroom. If noise wakes you during the light cycles of sleep, use white noise or earplugs.
- Cut out caffeine eight hours before bedtime.
- Avoid alcohol at least four hours before bedtime.
- Stop eating at least two hours before bedtime, especially considering spicy foods or those high in fat, such as fried foods and those containing full-fat dairy, and acidic foods like tomatoes.
- Avoid overeating, as the body may take longer to digest the nightly meal to fall asleep.
For more recommendations on what not to do in the hours before bedtime, see our article 10-3-2-1-0 Sleep Rule to ensure you get enough good quality sleep and wake up refreshed.
Understanding sleep cycles takes on a new priority when you become a parent for the first time. To help members on their parenthood journey, HIF has partnered with Sleep Eazzzy Baby. With a HIF Domestic Hospital product that includes pregnancy and birth cover, you can access Nourish Baby’s online learning hub with sleep and settling support from qualified early parenting consultants. For more information, see our Sleep Eazzzy Baby page.