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Does the BRAIN sleep?

When we are asleep, the brain does not entirely “shut down”. It is still possible to record brain wave activity which indicates that the brain still functions, but performs tasks that differ from those during the day. A large part of the brain stem must be kept working, including the medulla oblongata, pons, and hypothalamus. They control vital functions such as breathing, heartbeat, body temperature and blood pressure regulation. Therefore, even when you are sleeping, the brain must stay active.

We need sufficient sleep to allow the brain to have enough time to conduct its functions. How much sleep is adequate? The answer may vary from person to person, but under normal circumstances, babies need about 16-18 hours of sleep per day; school-age children and teens need about 9.5 hours of sleep per day; most adults need about 7-9 hours of sleep per day; from age 60 onward, the required amount of sleep time gradually decreases.

Sleep Cycle


Throughout the night sleeping, brain and physical activity change according to the “sleep cycle”. The sleep cycle is primarily composed of two states, rapid eye movement (REM) and non-rapid eye movement (NREM). The human body will first go through the 1 to 3 stages of NREM, then the REM stage. The rest of the sleep time will not stay in REM, but continuously shifts between NREM and REM. This is the sleep cycle.

The REM stage of the first sleep cycle lasts for a few minutes. Each REM stage gradually increases in time until the last sleep cycle, which may be as long as an hour. An average person experiences 4 to 6 sleep cycles every night, each cycle lasting about 90 to 120 minutes. Brain waves, eye movements, muscle tension, etc. are different at each stage.

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Stage N1

Transitional Sleep


This stage is the lightest stage of sleep, eyes are closed, but the body will be in a state of “alert” and is easily awakened. In general, the time spent in stage N1 increases with age.


Stage N2

Intermediate Sleep


This stage accounts for about half of the overall sleep time. Brain activity and the heartbeat will slow down, the body temperature will drop, and the body is ready to enter deeper sleep.


Stage N3

Deep Sleep


This stage is deep sleep, also known as slow wave sleep. The human body’s heartbeat and breathing are reduced to the lowest level, and the muscles of the whole body are also relaxed, allowing the body to recover.



This stage accounts for about 20-25% of the total sleep time of adults. Most dreams occur at this stage, eyes pulsate left and right, breathing will become faster, heart rate and blood pressure will also increase. According to the National Sleep Foundation, REM is beneficial to learning, memory and emotional development.

2 Major Brain Functions

while you are asleep

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Reorganize the Brain & Strengthen Memory Retention


Since the brain is busy processing large amounts of sensorial information during the day, there is not enough time to prioritize which memories need to the preserved. When we are asleep, amount of sensual data received is reduced compared to when being awake. Therefore, this period is essential for the brain to reorganize information and strengthen memories.

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Detox Brain’s Waste Material


During sleep, the speed of cerebrospinal fluid flow in the brain will accelerate. The process is like a "vacuum cleaner" removing toxins accumulated in the brain during the day. Also, from a series of mouse experiments, researchers found that activity in the glymphatic system (the brain's waste removal system) increased by about ten times during sleep. At the same time, sleep significantly cleared a protein from the brain called beta-amyloid (a toxin believed to be associated with brain degeneration).


[1]ᅠAmerican Sleep Association. What is sleep? Accessed 16/1/2019., National Sleep Foundation. Debunking sleep myths: Does your brain shut down when you sleep? Accessed 16/1/2019., National Sleep Foundation. How sleep works: What happens when you sleep. Accessed 16/1/2019., National Institute of Neurological Diseases and Stroke. Brain basics: Understanding sleep. Accessed 16/1/2019.

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