Impact of sleeping environment on sleep quality
Whereas animals have rest-activity cycles driven by changes in light and temperature, humans are influenced by a variety of cues such as alarm clocks, alterations in the outdoor light (sunsets), rapid changes in temperature, and social activities. However, like other animals we also follow an internal rhythm. This endogenous rhythm, which follows a period of nearly 24 hours, drives sleep-wake cycles, modifications in body temperature and other physiologic parameters; but many decades ago, time-isolation experiments showed that humans have a natural tendency to sleep at a slightly different frequency from the most adaptive 24-hour rhythm. This circadian rhythm is closer to 25 hours and has to be reset each day – by zeitgebers or external cues. The circadian rhythm links sleep behavior to body temperature: body temperature decreases, not only as a function of circadian rhythm phase, but also as a function of sleep. When a person is asleep, central control of body temperature is decreased, and at certain sleep stages when this control is suspended the body relies on an equilibrium with its environment.