Is the brain not resting during sleep? What are the true roles of non-REM and REM sleep!?
Hello!
This is Takahashi, the lead trainer at Small Gym Pain Free.
We often tend to think that "sleep is for resting the brain," but in reality, the brain is actively working even while we sleep.
Two types of sleep are particularly important: non-REM sleep and REM sleep. Each has a different role, and both are essential for maintaining health and brain function.
Today, I will delve a little deeper into that topic.
Non-REM sleep is the brain's "time for tidying up"
During non-REM sleep, the nerve cells in the cerebral cortex are in a state where they simultaneously repeat activity and rest.
Therefore, it is said that the brain is not completely resting, and the amount of brain activity itself is not much different from when awake.
However, because reactions to external stimuli decrease and consciousness also lowers, the brain enters a state where it can concentrate on internal tasks.
The tasks being performed during this time are
• Memory organization
• Information processing
.
For example, information obtained during the day is temporarily stored in the hippocampus, but during sleep, it is sorted into "necessary memories" and "unnecessary memories." Then, the necessary information moves to the neocortex and becomes long-term memory.
Think of it like the closing procedures performed after a shop closes or the preparations for opening the next day.
As I mentioned yesterday, non-REM sleep is divided into three stages.
• N1 (Initial sleep)
The stage where you start to fall asleep and your muscles begin to relax.
• N2 (Moderate sleep)
Body temperature drops and heart rate stabilizes.
• N3 (Deep sleep)
The deepest sleep where delta waves appear. During this stage, growth hormone is actively secreted, and the body's recovery and repair progress.
Also, during this deep non-REM sleep, the glymphatic system, which discharges waste products from the brain, is thought to work actively, removing unnecessary substances such as amyloid-beta. This plays an important role in future brain health as well.
REM sleep is "sleep where the brain is actively moving"
On the other hand, REM sleep has characteristics that are completely different from non-REM sleep.
During REM sleep,
• The eyeballs move rapidly
• Cerebral blood flow increases
• Brain activity is close to being awake
is the state.
However, "REM atonia" occurs, where muscles other than the eyeballs and respiratory muscles are completely relaxed so that the body does not move.
It is also during this REM sleep that we dream.
The dullness of reaction to external stimuli is almost the same as N2 to N3 of non-REM sleep. Therefore, it is easier to understand REM sleep as a different type of sleep from non-REM sleep rather than "light sleep."
Does less REM sleep increase health risks!?
An interesting study shows the relationship between a decrease in REM sleep and health risks.
According to the study,
• A 1% decrease in REM sleep increases dementia risk by about 9%
• For every 5% decrease in REM sleep, the mortality rate increases by 13%
is reported.
Since the proportion of REM sleep decreases with age, it becomes important to be conscious of sleep quality as you get older.
In particular, its connection to Alzheimer's disease, a type of dementia, is also being studied.
Summary
Sleep is not just rest, but a maintenance time for the brain and body.
• Non-REM sleep
→ Memory organization, physical recovery, removal of brain waste
• REM sleep
→ Memory integration, brain network adjustment
Our brains maintain health by repeating these two in a balanced manner.
Quality sleep may also affect future cognitive function and lifespan.
Let's cherish our daily sleep not just as rest, but as "brain maintenance time" (^^)
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