CHAPTER 3

The Need for Slumber

PART 1 Physiology of Sleep

Quantifying Sleep
It used to be thought that sleep was a void, a shutting down of the brain and body. All that changed when scientists began using electroencephalograms (EEGs) to monitor the brain’s characteristic electrical patterns during sleep. It became clear that sleep is an active, dynamic state. By monitoring eye movements and brain waves, researchers have been able to differentiate between the two main types of sleep as well as distinguish the stages of sleep.

PART 2 Why Do We Need to Sleep?

Humans have probed the puzzle of why we need to sleep for eons—and we still don’t know the answer. William Dement, founder of Stanford University’s Sleep Research Center, conducted research on sleep for 50 years. When asked why people need to sleep, he replied, “As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy.” READ MORE

There are many theories:

Survival. Because animals that remain inactive when it’s dark are less likely to be killed by predators, perhaps sleep evolved as a protective mechanism.

Energy conservation. Energy metabolism is reduced by as much as 10% in humans.

Resting the heart. During non-REM sleep, there’s an overall reduction in your heart rate and blood pressure. (However, blood pressure and heart rate increase during REM sleep.)

Rejuvenation of the body. Many of the body’s major restorative activities, including tissue repair, muscle growth, protein production, and growth hormone release happen mostly, or only, during sleep.

Rejuvenation of the brain. The brain may need sleep to enable it to function well during wakeful hours. For instance, when you’re awake, brain neurons produce adenosine, a by-product of cellular activity. It builds up over the hours and is thought to be one factor in making you feel tired. When you sleep, your body clears the adenosine from your system, making you feel more alert when you wake up.

Researchers have found that activity in the parts of the brain that control emotions, decision-making, and social interactions is greatly reduced during deep sleep. It may be that these areas of the brain need to rest during sleep.

Brain structure and organization. It’s becoming clear that sleep plays a big role in how the brain changes its structure and organization as we grow, develop, learn new things, and perform different tasks. Infants spend 13-14 hours a day sleeping, and about half of that time is spent in REM sleep. Sleep experiments show that an adult’s ability to learn and perform a number of different tasks is greatly hindered by lack of sleep.

Dreaming. Most dreams occur during REM sleep, although night terrors occur during non-REM sleep. Some sleep experts suggest that dreams have a critical role in the formation of memories. Others think that dreams are a subjective interpretation of signals generated by the brain’s limbic system. Another theory proposes that dreams clean up clutter from the mind.

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PART 3 What Happens When You’re Deprived of Sleep?

Just the Facts

World Record

Animals that are completely deprived of sleep lose all immune function and die in a matter of weeks. For example, rats (which normally live 2-3 years) that are deprived of REM sleep survive only about 5 weeks on average. Rats deprived of all sleep stages live only about 3 weeks. READ MORE

In humans, too little sleep leaves us drowsy and unable to concentrate the next day and also impairs our physical performance, including hand-eye coordination and reaction time; judgment; memory; and ability to do math. Continued lack of sleep leads to mood swings and hallucinations. Marathon sleep resister Randy Gardner, who was documented to have stayed awake for 11 days, was reported by one person monitoring him to have become paranoid and have hallucinations. LESS