What is Sleep?
Featured content
Sleep Lab
How do shift work and sleep apnea affect an individual's sleep patterns? Explore these and other questions in the Sleep Lab.
launch interactive
Brain Activity during REM Sleep (0:29)
Dr. Steven Shea describes the patterns of activity sleep scientists see in people during REM sleep.
watch video
Sleep Patterns across the Night (0:46)
Dr. Thomas Scammell describes patterns of brain activity people typically experience over the course of a night of sleep.
watch video
We all have at least a vague notion of what sleep is, but that doesn't mean that defining this mysterious part of our lives is simple. After all, detailed analysis of our own sleep isn't really an option, given that we rarely know that we're sleeping when we're asleep. And even if we observe the sleep of others, so much of what they experience—changes in the functions of their brains and bodies—is not easily seen from the outside.
Sleep scientists have explored these changes in depth, and their definition of sleep is tied to characteristic patterns of brain waves and other physiological functions. Features in this section describe and explain the significance of typical sleep patterns, as well as a variety of factors that disrupt these patterns.
The Characteristics of Sleep
Although a sleeping person may appear inactive, some functions of the brain and body are actually more active during sleep than when we're awake. more
Natural Patterns of Sleep
We require various types and depths of sleep in different amounts and at different times over the course of the night, but scientists aren't entirely sure why. more
Sleep Lab
Just as many other human characteristics vary from one person to another, sleep patterns can vary greatly depending on age, work schedule, health, and other factors. more