This is the definitive book on sleep!  It is loaded with gems: Your sleep drive keeps an exact tally of accumulated waking hours. Like bricks in a backpack, accumulated sleep drive is a burden that weighs down on you. Every hour that you are awake adds another brick to the pack. The brain’s sleep load increases until you go to sleep when the load starts to lighten.

The author emphasizes that your brain keeps an exact accounting of how much sleep it is owed.  Each successive night of partial sleep loss is carried over and the end effect appears to accumulate in a precisely additive fashion. Accumulated lost sleep is like a monetary debt: “It must be paid back.”

Overthrowing Our Biological Clocks

In just a few decades of technological innovation we have managed to totally overthrow our magnificently evolved biological clocks and the complex biorhythms they regulate.

Our loss of sleep time and natural rhythms is the tragic legacy of a single and profound advance-the light bulb. Electric lights not only let people stay up longer, they also were bright enough to mimic the light and significantly shift people’s internal biological clocks. When bedtime shifted to 10 or 11 p.m. instead of 8 or 9 p.m., midnight was no longer the middle of the night.

The incandescent bulb marked the beginning of the modern era of sleeplessness, and Edison was by no means ignorant of the implications of his breakthrough. A restless genius and experimenter, Edison believed that too much sleep was bad for you. Edison thought that people got twice as much sleep as they needed and the extra sleep made them “unhealthy and inefficient.”

Sunlight Had Been the Standard

Edison’s invention of bright electric lights threw a wrench into the human clockworks. Over millions of years, our bodies and minds had evolved using sunlight as a Universal Standard Time (UST), as the infallible index against which we set our internal clock.

We have grown so accustomed to living year round in an artificial summer of light, with long days and short nights, that it is difficult to image life before electric lights and contemporary work schedules. Our bodies, however, have not forgotten. Can we believe that in 100 years our bodies can so easily change needs buried deep within the workings of each cell?

Many people work long hard hours throughout the week hoping to catch up on sleep over the weekend. They collapse in the bed on Friday night and sleep deeply until late in the morning. Even though they have paid back several hours of sleep debt, they walk around like zombies all day Saturday, barely able to stay awake. The reason is obvious: you cannot pay back a weeks worth of sleep debt in one night. Less obvious: the stressful arousal of the weekday work place is no longer masking sleep debt on Saturday. As people tend to drink and eat more on weekends, their sleep fighting arousal is further suppressed.

Deprivation

All wakefulness is sleep deprivation. You build up sleep debt over the course of the day, and then pay it off as you sleep that night. If you get an hour less than you need, you carry an hour of sleep debt into the next day, and your drive for sleep becomes stronger. Sleep debt accumulates in an additive fashion, so that if you get one hour less sleep than you need for each of eight nights your brain will then tend toward sleep as strongly as if you had stayed up all night.

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