Surprisingly, they are as different from each other as either is from waking. Scientists divide sleep into two major types: The hormone induces drowsiness, and scientists believe its daily light-sensitive cycles help keep the sleep/wake cycle on track. Levels of melatonin begin climbing after dark and ebb after dawn. As a person reads clocks, follows work and train schedules, and demands that the body remain alert for certain tasks and social events, there is cognitive pressure to stay on schedule.

The circadian rhythm disturbances and sleep problems that affect up to 90% of blind people demonstrate the importance of light to sleep/wake patterns. However, exposure at the wrong time can shift sleep and wakefulness to undesired times. Exposure to light at the right time helps keep the circadian clock on the correct time schedule. In societies where taking a siesta is the norm, people can respond to their bodies’ daily dips in alertness with a one- to two-hour afternoon nap during the workday and a correspondingly shorter sleep at night. Most Americans sleep during the night as dictated by their circadian rhythms, although many who work on weekdays nap in the afternoon on the weekends. When the investigators plotted the times when unplanned naps occurred, they found peaks between 2 a.m.

Not surprisingly, many slipped into naps despite their best efforts not to. In one study, researchers instructed a group of people to try to stay awake for 24 hours. (“Circadian” means “about a day.”) This internal clock, which gradually becomes established during the first months of life, controls the daily ups and downs of biological patterns, including body temperature, blood pressure, and the release of hormones.Ĭircadian rhythms make people’s desire for sleep strongest between midnight and dawn, and to a lesser extent in mid-afternoon. For instance, a pacemaker-like mechanism in the brain regulates circadian rhythms. Your internal clock (circadian rhythms)Ĭertain brain structures and chemicals produce the states of sleeping and waking. Quiet sleep is important because it helps restore the body, while REM sleep restores the mind and is important for both learning and memory. During the night, these stages of quiet sleep alternate with periods of REM (dreaming) sleep. Each stage of sleep serves an important purpose in keeping your brain and body healthy. People progress through a series of distinct physiological stages during sleep. Your body’s natural daily rhythms are regulated by structures in the brain that help determine when you fall asleep and wake up. A Harvard Health article The Science of Sleep: Stages and Cycles Circadian Rhythms, Sleep Stages, and Sleep Architecture

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