1. Two Types of Sleep: REM and Non-REM
While you are asleep, two types of sleep alternate. One is "REM sleep," where your eyes move rapidly and your brain is active. The other is "non-REM sleep," where both your brain and body are deeply resting.[1] REM and non-REM sleep form a set that repeats about 3 to 6 times during one night.[1]
2. How Sleep Helps Wash Waste Out of the Brain
A clear fluid called cerebrospinal fluid flows around the brain. It is thought that during sleep, this fluid flows through the gaps in the brain to wash away waste products that are no longer needed.[2] This mechanism is called the "glymphatic system."[2]
3. How Sleep Helps the Brain Organize Memories
Both REM and non-REM sleep are involved in organizing memory. During deep non-REM sleep, things learned that day become active in the brain again. During REM sleep, this activity helps fix those memories into the brain.[7] The two types of sleep support each other by playing different roles.[7] There is also research showing that the pattern of REM sleep changes on days when you study or practice hard.[3]
4. Why Deep Sleep Releases Growth Hormone
During the first deep non-REM sleep after falling asleep, large amounts of "growth hormone" are released.[4] It is said that getting deep sleep is more important than the specific time on the clock.[4]
5. What Happened When Randy Gardner Stayed Awake for 11 Days
In 1964, a 17-year-old American high school student named Randy Gardner stayed awake for 264 hours (11 days) as a winter vacation project.[5] Sleep researchers from a university and a military doctor who monitored his health were present.[5] As the days passed, his concentration dropped, his mood became unstable, and he began to see things that looked like hallucinations.[5] After he ended the attempt, he slept longer than usual and returned to his normal state in about 2 days.[5] However, this is very dangerous, so you must never try to copy it.[5]
Although this record was broken several times later, in 1997, Guinness World Records stopped monitoring and measuring sleep deprivation records.[5] They did this because of the dangers of lack of sleep and the difficulty of measuring "microsleeps," which are momentary dozing episodes.[5]
6. How Much Sleep Different Animals Need
Koalas sleep for 18 to 22 hours a day.[6] The eucalyptus leaves they eat have low nutritional value and are hard to digest, requiring a lot of energy for digestion. It is thought that they conserve energy for other activities by sleeping so much.[6] On the other hand, giraffes are animals that lie down to sleep for very short times.[6] In a study of wild giraffes, the time spent in deep sleep (REM sleep), characterized by lying on the ground with the neck bent greatly, averaged less than 10 minutes per night.[6] However, the time they stand still is much longer. Researchers say it is not easy to decide exactly what counts as a giraffe's "sleep."[6]
7. How to Track Your Own Sleep for One Week
For one week, try writing down the time you went to bed and the time you woke up in a notebook.[1] Compare how much you slept on different days. It might be interesting to record if your mood or concentration in the morning is different on days you slept well versus days you lacked sleep.[1]