Sleep

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.