<For those who think it's not a big deal that you slept less than an hour>

<For those who think it's not a big deal that you slept less than an hour>

1. Over the years, researchers have found that two stages of sleep (rem sleep, non-rem sleep) repeat a push-and-pull struggle to take over the brain overnight.

2. (Generally) a war between both sides for the brain is won or lost every 90 minutes. At first, non-REM sleep wins, but as time passes, REM sleep retakes. Tracking this flow, which fluctuates throughout the night, we can see that a very beautiful circulation structure is created.

3. So why do non-REM and REM sleep cycles repeat so much? Scientists have different views on why our sleep cycle is extremely asymmetric even though it is repeated. Numerous theories have been put forward.

4. In response, I (= Matthew Walker) theorized that non-REM sleep and REM sleep interactions are necessary to reorganize and update our neural circuits at night, thereby managing the limited storage space in the brain.

5. In other words, because the storage capacity is determined in the memory structure, our brain must find an excellent balance between retaining existing information and securing enough storage space for new information. As a result, thinning and eliminating unnecessary neural connections is one of the key components of deep non-REM sleep, which accounts for the majority of sleep time when you first fall asleep.

6. Conversely, REM sleep, which accounts for most of the latter half of sleep time, serves to strengthen this connection through dreams.

7. In other words, in the early stages of sleep, non-REM sleep leads to the overall deletion of (unnecessary information), and later, information is mixed and connected and added to each other in detail through REM sleep.

8. Our memory lists must also be updated endlessly because our life experiences are constantly changing. As a result, the brain needs to go back to sleep anew all the time. Each night, the various sleep stages allow us to automatically update our memory networks based on the events of the previous day.

9. (In other words, sleep is the role of updating our brain's memory, and sleep deprivation means this update is not working properly.)

10. However, there is a danger to this asymmetric sleep pattern. Suppose that you, who usually sleeps from 12 p.m. to 8 a.m., have to wake up at 6 a.m. instead of 8 a.m. because of a meeting that opens early in the morning. So how much less sleep did you get?

11. Logically, it's 25%. I woke up at 6 a.m., so I slept only 2 hours less than I normally slept 8 hours.

12. But the answer is wrong. Because our brain places most of the REM sleep we need at the end of our sleep, or near the morning, it seems like we have lost 25% simply in terms of time, but in terms of REM sleep, you have lost 60% to 90%.

13. Likewise, this loss works in both directions. If you fall asleep two hours later than usual, you lose a significant portion of your deep sleep (non-REM sleep).

14. Just as eating only carbohydrates without protein leads to malnutrition, the imbalance between non-REM and REM sleep harms the health of the body and mind in many ways.

15. (It's easy to think that going to bed one hour less late or less isn't a big deal, but going to bed one hour less has a big impact on either of them in terms of REM-non-REM sleep balance.)

- Matthew Walker in "Why Do We Sleep?"