Sleep and Dreaming

Most adults need seven to nine hours of sleep to recuperate from physical exertion, as well as to consolidate learning and memory.

Circadian rhythms are physical, mental, and behavioral changes that respond to light and darkness and are important in determining human sleep patterns.

Sleep proceeds through multiple cycles of non-REM (3 stages) and REM per night, with each full cycle lasting between 90 and 110 minutes.

Sleep disorders cause sleep disturbances that affect the amount, quality, or timing of sleep or that induce abnormal events during sleep.

Numerous theories, both psychological and neurobiological, have been proposed to explain the elusive mystery of the purpose of dreaming.