Sleep

sleep, resting state in which an individual becomes relatively quiescent and relatively unaware of the environment. During sleep, which is in part a period of rest and relaxation, most physiological functions such as body temperature, blood pressure, and rate of breathing and heartbeat decrease. However, sleep is also a time of repair and growth, and some tissues, e.g., epithelium, proliferate more rapidly during sleep. Sleep also aids in the strengthening of memories, and researchers have discovered that an increased circulation of fluids in the brain during sleep removes waste products from the brain.

In humans, sleep occurs in cyclical patterns; in each cycle of 11/2 to 2 hr, the sleeper moves through four stages of sleep, from Stage 1 to Stage 4, and back again to Stage 1. In the first stage, low-frequency, low-amplitude theta waves characterize brain activity. The stage usually lasts only several minutes, before the individual drifts into Stage 2 sleep, and the brain moves into low-frequency, high-amplitude waves. Stage 3 signals an increase of low-frequency, high-amplitude delta waves, and at Stage 4 sleep these delta waves account for more than half of all brain wave activity (see electroencephalography). Rapid-eye-movement (REM) sleep occurs during Stage 1 sleep at the end of each cycle, and people woken up at this time usually report that they have been dreaming. Dream deprivation or sleep deprivation results in detrimental changes in personality, perceptual processes, and intellectual functioning. There is some evidence that emotional and environmental deprivation disrupts the sleep patterns of young children, which in turn inhibits the secretion of growth hormone, normally secreted maximally during sleep.

The amount of sleep needed depends on both the individual and the environment: For instance, worrying, critical individuals tend to need both more sleep and more dream sleep than easygoing ones, and stress and worry during the day result in an increase in REM sleep. It has been hypothesized that while deeper stages of sleep are physically restorative, REM sleep is psychically restorative. REM sleep is also believed to integrate new information in the brain and to reactivate the sleeping brain without waking the sleeper. There is evidence that the hypothalamus and thalamus of the brain initiate sleep and that part of the midbrain acts as an arousal system. See also dream; insomnia; narcolepsy; sleep apnea.

The Columbia Encyclopedia, 6th ed. Copyright© 2018, The Columbia University Press.

Sleep: Selected full-text books and articles

The Fall of Sleep By Jean-Luc Nancy; Charlotte Mandell Fordham University Press, 2009
The Neuropsychology of Sleep and Dreaming By Mario Bertini; John S. Antrobus Lawrence Erlbaum Associates, 1992
Sleep Habits and Patterns of College Students: An Expanded Study By Buboltz, Walter, Jr.; Jenkins, Steve M.; Soper, Barlow; Woller, Kevin; Johnson, Patrick; Faes, Theresa Journal of College Counseling, Vol. 12, No. 2, Fall 2009
PEER-REVIEWED PERIODICAL
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
Preschoolers' Sleep: Current U.S. Community Data within a Historical and Sociocultural Context By Keefe-Cooperman, Kathleen; Brady-Amoon, Peggy Journal of Early Childhood and Infant Psychology, Vol. 8, Annual 2012
PEER-REVIEWED PERIODICAL
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
The Effects of Sleep on Academic Performance and Job Performance By Chiang, Yu-Chih; Arendt, Susan W.; Zheng, Tianshu; Hanisch, Kathy A College Student Journal, Vol. 48, No. 1, March 2014
Sleep on It, but Only If It Is Difficult: Effects of Sleep on Problem Solving By Sio, Ut Na; Monaghan, Padraic; Ormerod, Tom Memory & Cognition, Vol. 41, No. 2, February 2013
PEER-REVIEWED PERIODICAL
Peer-reviewed publications on Questia are publications containing articles which were subject to evaluation for accuracy and substance by professional peers of the article's author(s).
Determinants of Sleep Duration and Sleep Quality: Gender Differences, Coping and Health Outcome By Kirkcaldy, Bruce; Partonen, Timo International Journal of Child Health and Human Development, Vol. 4, No. 2, April 1, 2011
Secrets of Sleep By Alexander Borbely; Deborah Schneider Basic Books, 1986
Children's Sleep: Sketching Historical Change By Stearns, Peter N.; Rowland, Perrin; Giarnella, Lori Journal of Social History, Vol. 30, No. 2, Winter 1996
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