What does the body do while it is sleeping? And how can you ensure you get a better night’s rest? The answers to these questions start with the human mind.
Let’s break it down.
While you rest the brain is working hard to store memories, heal tissues, and restore the body. To do all this it passes through a total of four stages of sleep several times each night. These stages are categorized as both REM and Non-REM sleep.
Before 2007 experts considered there to be 5 sleep stages, including REM, but most medical professionals today would agree that there are only 4.
“We basically divide sleep into wake, non-REM — three types — and REM sleep.”
Dr. Lois Krahn, Mayo Clinic
A full sleep cycle lasts around 90 minutes and consists of all 4 stages. Sleepers move from stage 1, light sleep and through all the phases until they are in stage 3, deep sleep. The last is where dreaming occurs and is called Rapid Eye Movement (REM) Sleep.
Sleepers do not simply end a cycle and begin again. After moving from light sleep to deep sleep, the cycle reverses from stage 3 deep sleep to stage 1 light sleep before moving into REM and beginning with stage 1 once again.
For centuries people believed sleep to be a passive event, but in 1953, through the use of Electroencephalography (EEG) machines, scientists Nathaniel Kleitman and Eugene Aserinksy were able to determine that the body passes through several complex stages of sleep.
EEG’s record electrical brain activity. With electrodes placed on certain parts of the scalp, this noninvasive method is often used to measure wave patterns in the brain while participants are sleeping.
In this setting, the EEG is placed on the sleeper and monitored by scientist and medical professionals during a Polysomnography, better known as a sleep study. This is done to better understand sleep patterns and diagnose potential sleeping disorders.
This is when the body is first falling asleep. If aroused in this phase, many people would not even realize they were asleep. Although the eyes are closed, sleepers are typically still aware of their surroundings.
Heart and breathing slow.
Brain activity slows by about 50%.
Sleepers fall into a deeper sleep and their bodies go into a more relaxed state that would be harder to wake up from. With a full night’s rest, this stage may be where sleepers experience the most sleep.
Body temperature drops, digestion speeds decrease, respiratory and heart rates rate slows down.
As brain activity continues to decrease and brain waves spread out, there are intermittent Sleep Spindles, a higher burst and frequency of brain waves. The cause of these spindles is unknown.
This phase is often referred to as slow wave or delta wave sleep. There are two parts to this stage, with the second part being more intense. Sleepers are not as affected to external stimuli in this phase, making it much harder to arouse them.
45-90 minutes (decreases with each sleep cycle).
The body repairs tissues, builds muscle and bone, and reinforces the immune system. Blood pressure drops further as do respiratory rate and body temperature.
Slower and larger brain waves appear as the body relaxes and begins to repair itself.
After reversing back through the other three stages of sleep, the body enters REM or dream sleep. To prevent the sleeper from acting out dreams, the brain releases chemicals that paralyze the body, allowing the muscles to relax. This phrase first occurs anywhere between 90 to 120 minutes after falling asleep.
10 to 60 minutes (increases with each sleep cycle.
Rapid eye movement, accelerated respiration and heart rate, increased brain activity, and muscle relaxation.
Rapid increases in cerebral activity in part due to dreaming.
Light sleep is characterized by stages 1 and 2 of the sleep cycle. During these phases, the sleeper’s subconscious is much more aware of external stimuli, making it easier to wake up. It is believed that sleep spindles in phase 2 may be important to learning, as this may be where memories are processed from short term to long term memory.
Deep sleep, or stage 3, is when the body works to heal tissues and grow new cells. As an individuals sleep cycle progresses they spend less time in deep sleep and more in REM. When people feel exhausted due to lack of rest, it may be because they are not spending enough time in slow wave sleep.
Taking an hour and a half nap is a good way to catch up on this type of sleep, as this is about the length of a full sleep cycle. Seeing as the first sleep cycle is longest, this should allow sleepers to spend the maximum amount of time in stage 3.
When do we dream?
Dreaming takes place during the REM stage. This is when the brain becomes more active, triggering dreams to dance in the mind’s eye and causing chemicals to be released to prevent the body from acting out the dreams. Behind the eyelids, the sleeper’s eyes flash back and forth, hence the name of the stage Rapid Eye Movement.
Why is REM so important?
The body does some restoration during REM sleep, but REM could potentially be contributing so much more. REM has been considered to be a learning phase where the subconscious mind interprets the day’s events so sleepers can perceive waking life in a new light. REM is also heavily linked with learning and memory abilities in small children as well as adults.
“During the rapid eye movement (REM) stage of sleep, your brain sorts the important information from the unimportant and files long-term memory. If this stage of your sleep cycle is shortchanged, your mental focus and acuity may decrease. Plus, you may feel cranky and short-tempered.”
Stacy M. Peterson and Brooke L. Werneburg, Mayo Clinic
Do Sleep Cycles change with age?
Yes, they certainly do. Infants may spend up to half of their cycle in REM while adults only spend about 20%. When it comes to deep sleep, people 30 and younger spend about 2 hours a night here, while folks 65 and older may only get 30 minutes of slow-wave sleep. EEG’s indicate that adults may actually spend most of their nighttime rest in a lighter sleep, at Stage 2.
Like everything, the best way to learn about something is to experience it. So get some sleep tonight and try to pay attention to how you feel and how much time you reckon you spend in each cycle.
Analyzing part of your REM stage may be easiest, as this is where sleepers typically wake up. If you’re up to it, keep a dream journal and track your sleep that way. This can help you to be consciously aware of what you are thinking about while you snooze.
A sleep schedule could also be a useful trick. Simply track the time you fall asleep and wake up, and hopefully this could help you figure out how long your sleep cycle is. If you find something that works or want to share your story, reach out in the comments below, we love to hear from our readers.