# Why We Sleep  ## Metadata - Author: [[Matthew Walker]] - Full Title: Why We Sleep - Category: #books ## Highlights - memories were being “replayed” at the level of brain-cell activity as the rats snoozed. ([Location 640](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=640)) - During REM sleep, the memories were being replayed far more slowly: at just half or quarter the speed of that measured when the rats were awake and learning the maze. ([Location 641](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=641)) - Since your brain desires most of its REM sleep in the last part of the night, which is to say the late-morning hours, you will lose 60 to 90 percent of all your REM sleep, ([Location 715](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=715)) - even though you are losing 25 percent of your total sleep time. ([Location 716](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=716)) - think of the wake state principally as reception (experiencing and constantly learning the world around you), NREM sleep as reflection (storing and strengthening those raw ingredients of new facts and skills), and REM sleep as integration (interconnecting these raw ingredients with each other, with all past experiences, and, in doing so, building an ever more accurate model of how the world works, including innovative insights and problem-solving abilities). ([Location 827](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=827)) - brain will consume a far larger portion of deep NREM sleep than of REM sleep on the first night after total sleep deprivation, expressing a lopsided hunger. ([Location 996](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=996)) - Should you keep recording sleep across a second, third, and even fourth recovery night, there’s a reversal. Now REM sleep becomes the primary dish of choice with each returning visit to the recovery buffet table, with a side of NREM sleep added. Both sleep stages are therefore essential. ([Location 999](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=999)) - However, those that abandoned regular siestas went on to suffer a 37 percent increased risk of death from heart disease across the six-year period, relative to those who maintained regular daytime naps. The effect was especially strong in workingmen, where the ensuing mortality risk of not napping increased by well over 60 percent. ([Location 1124](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=1124)) - It is perhaps unsurprising that in the small enclaves of Greece where siestas still remain intact, such as the island of Ikaria, men are nearly four times as likely to reach the age of ninety as American males. ([Location 1127](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=1127)) - The total amount of time we spend asleep is markedly shorter than all other primates (eight hours, relative to the ten to fifteen hours of sleep observed in all other primates), yet we have a disproportionate amount of REM sleep, the stage in which we dream. Between 20 and 25 percent of our sleep time is dedicated to REM sleep dreaming, compared to an average of only 9 percent across all other primates! ([Location 1138](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=1138)) - Autistic individuals show a 30 to 50 percent deficit in the amount of REM sleep they obtain, relative to children without autism. ([Location 1294](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=1294)) - Of concern is that administering caffeine to juvenile rats will also disrupt deep NREM sleep and, as a consequence, delay numerous measures of brain maturation and the development of social activity, independent grooming, and the exploration of the environment—measures of self-motivated learning. ([Location 1440](https://readwise.io/to_kindle?action=open&asin=B06ZZ1YGJ5&location=1440))