Acebo C, Millman RP, Rosenberg C, Cavallo A, Carskadon MA. Sleep, breathing, and cephalometrics in older children and young adults. Part I: Normative values. Chest. 1996;109(3):664–672. [PubMed: 8617074]
Adair RH, Bauchner H. Sleep problems in childhood. Current Problems in Pediatrics. 1993;23(4):142, 147–170. [PubMed: 8500344]
Ancoli-Israel S. Insomnia in the elderly: A review for the primary care practitioner. Sleep: Supplement. 2000;23(1):S23–S30. discussion S36–S38. [PubMed: 10755805]
Ancoli-Israel S. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2005. Normal human sleep at different ages: Sleep in older adults; pp. 21–26.
Anders TF, Sadeh A, Appareddy V. Normal sleep in neonates and children. In: Ferber RKM, editor. Principles and Practice of Sleep Medicine in the Child. Philadelphia: Saunders; 1995. pp. 7–18.
Astrom C, Trojaborg W. Relationship of age to power spectrum analysis of EEG during sleep. Journal of Clinical Neurophysiology. 1992;9(3):424–430. [PubMed: 1517410]
Bach V, Telliez F, Leke A, Libert JP. Gender-related sleep differences in neonates in thermoneutral and cool environments. Journal of Sleep Research. 2000;9(3):249–254. [PubMed: 11012863]
Bader G, Gillberg C, Johnson M, Kadesjö B, Rasmussen P. Activity and sleep in children with ADHD. Sleep. 2003;26:A136.
Beltramini AU, Hertzig ME. Sleep and bedtime behavior in preschool-aged children. Pediatrics. 1983;71(2):153–158. [PubMed: 6823416]
Bixler EO, Kales A, Jacoby JA, Soldatos CR, Vela-Bueno A. Nocturnal sleep and wakefulness: Effects of age and sex in normal sleepers. International Journal of Neuroscience. 1984;23(1):33–42. [PubMed: 6724815]
Blasi A, Jo J, Valladares E, Morgan BJ, Skatrud JB, Khoo MC. Cardiovascular variability after arousal from sleep: Time-varying spectral analysis. Journal of Applied Physiology. 2003;95(4):1394–1404. [PubMed: 12819215]
Bliwise D. Normal aging. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Saunders; 2005. pp. 24–38.
Bunning E. The Physiological Clock. Berlin, Germany: Springer-Verlag; 1964.
Buxton OM, Spiegel K, Van Cauter E. Modulation of endocrine function and metabolism by sleep and sleep loss. In: Lee-Chiong TL, Sateia MJ, Carskadon MA, editors. Sleep Medicine. Philadelphia: Hanley & Belfus; 2002. pp. 59–69.
Campbell SS, Gillin JC, Kripke DF, Erikson P, Clopton P. Gender differences in the circadian temperature rhythms of healthy elderly subjects: Relationships to sleep quality. Sleep. 1989;12(6):529–536. [PubMed: 2595176]
Carskadon MA. The second decade. In: Guilleminault C, editor. Sleeping and Waking Disorders: Indications and Techniques. Menlo Park, CA: Addison-Wesley; 1982. pp. 99–125.
Carskadon M, Dement W. Normal human sleep: An overview. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier Saunders; 2005. pp. 13–23.
Carskadon MA, Rechtschaffen A. Monitoring and staging human sleep. In: Kryger MH, Roth TT, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier Saunders; 2005. pp. 1359–1377.
Carskadon MA, Harvey K, Duke P, Anders TF, Litt IF, Dement WC. Pubertal changes in daytime sleepiness. Sleep. 1980;2(4):453–460. [PubMed: 7403744]
Carskadon MA, Orav EJ, Dement WC. Evolution of sleep and daytime sleepiness in adolescents. In: Guilleminault CLE, editor. Sleep/Wake Disorders: Natural History, Epidemiology, and Long-Term Evolution. New York: Raven Press; 1983. pp. 201–216.
Carskadon MA, Vieira C, Acebo C. Association between puberty and delayed phase preference. Sleep. 1993;16(3):258–262. [PubMed: 8506460]
Catcheside PG, Chiong SC, Mercer J, Saunders NA, McEvoy RD. Noninvasive cardiovascular markers of acoustically induced arousal from non-rapid-eye-movement sleep. Sleep. 2002;25(7):797–804. [PubMed: 12405616]
Chou TC, Scammell TE, Gooley JJ, Gaus SE, Saper CB, Lu J. Critical role of dorsomedial hypothalamic nucleus in a wide range of behavioral circadian rhythms. Journal of Neuroscience. 2003;23(33):10691–10702. [PubMed: 14627654]
Cianci T, Zoccoli G, Lenzi P, Franzini C. Loss of integrative control of peripheral circulation during desynchronized sleep. American Journal of Physiology. 1991;261(2 Pt 2):R373–R377. [PubMed: 1877696]
Crick F, Mitchison G. The function of dream sleep. Nature. 1983;304(5922):111–114. [PubMed: 6866101]
Davis KF, Parker KP, Montgomery GL. Sleep in infants and young children: Part one: Normal sleep. Journal of Pediatric Health Care. 2004;18(2):65–71. [PubMed: 15007289]
Dement W, Kleitman N. Cyclic variations in EEG during sleep and their relation to eye movements, body motility, and dreaming. Electroencephalography and Clinical Neurophysiology: Supplement. 1957a;9(4):673–690. [PubMed: 13480240]
Dement T, Kleitman N. The relation of eye movements during sleep to dream activity: An objective method for the study of dreaming. Journal of Experimental Psychology. 1957b;53(5):339–346. [PubMed: 13428941]
Dijk DCC. REM sleep as a gate to wakefulness during forced desynchrony in young and older people [abstract] Sleep. 1998;21(3):S298.
Dijk DJ, Beersma DG, van den Hoofdakker RH. All night spectral analysis of EEG sleep in young adult and middle-aged male subjects. Neurobiology of Aging. 1989;10(6):677–682. [PubMed: 2628779]
Dijk DJ, Duffy JF, Czeisler CA. Contribution of circadian physiology and sleep homeostasis to age-related changes in human sleep. Chronobiology International. 2000;17(3):285–311. [PubMed: 10841208]
Douglas NJ. Respiratory physiology: Control of ventilation. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier Saunders; 2005. pp. 224–229.
Driver HS, Shapiro CM. A longitudinal study of sleep stages in young women during pregnancy and postpartum. Sleep. 1992;15(5):449–453. [PubMed: 1455129]
Duffy JF, Dijk DJ, Klerman EB, Czeisler CA. Later endogenous circadian temperature nadir relative to an earlier wake time in older people. American Journal of Physiology. 1998;275(5 Pt 2):R1478–R1487. [PubMed: 9791064]
Dunlap JC, Loros JJ, DeCoursey PJ. Chronobiology: Biological Timekeeping. Sunderland, MA: Sinauer Associates; 2004.
Floras JS, Jones JV, Johnston JA, Brooks DE, Hassan MO, Sleight P. Arousal and the circadian rhythm of blood pressure. Clinical Science and Molecular Medicine Supplement. 1978;55(4):395s–397s. [PubMed: 282096]
Foley DJ, Monjan AA, Brown SL, Simonsick EM, Wallace RB, Blazer DG. Sleep complaints among elderly persons: An epidemiologic study of three communities. Sleep. 1995;18(6):425–432. [PubMed: 7481413]
Gais S, Molle M, Helms K, Born J. Learning-dependent increases in sleep spindle density. Journal of Neuroscience. 2002;22(15):6830–6834. [PubMed: 12151563]
Gaudreau H, Carrier J, Montplaisir J. Age-related modifications of NREM sleep EEG: From childhood to middle age. Journal of Sleep Research. 2001;10(3):165–172. [PubMed: 11696069]
Giannotti F, Cortesi F, Sebastiani T, Ottaviano S. Circadian preference, sleep and daytime behaviour in adolescence. Journal of Sleep Research. 2002;11(3):191–199. [PubMed: 12220314]
Gillette M, Abbott S. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2005. Fundamentals of the circadian system; pp. 131–138.
Goodman JD, Brodie C, Ayida GA. Restless leg syndrome in pregnancy. British Medical Journal. 1988;297(6656):1101–1102. [PMC free article: PMC1834895] [PubMed: 3143441]
Hertz G, Fast A, Feinsilver SH, Albertario CL, Schulman H, Fein AM. Sleep in normal late pregnancy. Sleep. 1992;15(3):246–251. [PubMed: 1621025]
Hoppenbrouwers T, Hodgman J, Arakawa K, Sterman MB. Polysomnographic sleep and waking states are similar in subsequent siblings of SIDS and control infants during the first six months of life. Sleep. 1989;12(3):265–276. [PubMed: 2740699]
Jenni OG, Carskadon MA. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2000. Normal human sleep at different ages: Infants to adolescents; pp. 11–19.
Jenni OG, O'Connor BB. Children’s sleep: An interplay between culture and biology. Pediatrics. 2005;115(1 Suppl):204–216. [PubMed: 15866854]
Jones BE. Basic mechanisms of sleep-wake states. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier/Saunders; 2005. pp. 136–153.
Karacan IH, Agnew H, Williams RL, Webb W, Ross J. Characteristics of sleep patterns during late pregnancy and postpartum periods. American Journal of Obstetrics and Gynecology. 1968;297(6656):1101–1102.
Karacan I, Anch M, Thornby JI, Okawa M, Williams RL. Longitudinal sleep patterns during pubertal growth: Four-year follow up. Pediatrics Research. 1975;9(11):842–846. [PubMed: 171619]
Kobayashi R, Kohsaka M, Fukuda N, Honma H, Sakakibara S, Koyama T. Gender differences in the sleep of middle-aged individuals. Psychiatry and Clinical Neurosciences. 1998;52(2):186–187. [PubMed: 9628142]
Krieger J. Respiratory physiology: Breathing in normal subjects. In: Kryger M, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier Saunders; 2000. pp. 229–241.
Laberge L, Petit D, Simard C, Vitaro F, Tremblay RE, Montplaisir J. Development of sleep patterns in early adolescence. Journal of Sleep Research. 2001;10(1):59–67. [PubMed: 11285056]
Landolt HP, Dijk DJ, Achermann P, Borbely AA. Effect of age on the sleep EEG: Slowwave activity and spindle frequency activity in young and middle-aged men. Brain Research. 1996;738(2):205–212. [PubMed: 8955514]
Lee KA, Zaffke ME. Longitudinal changes in fatigue and energy during pregnancy and the postpartum period. Journal of Obstetric, Gynecologic, and Neonatal Nursing. 1999;28(2):183–191. [PubMed: 10102546]
Lee KA, Zaffke ME, Baratte-Beebe K. Restless legs syndrome and sleep disturbance during pregnancy: The role of folate and iron. Journal of Women’s Health and Gender-based Medicine. 2001;10(4):335–341. [PubMed: 11445024]
Leibenluft E, Fiero PL, Rubinow DR. Effects of the menstrual cycle on dependent variables in mood disorder research. Archives of General Psychiatry. 1994;51(10):761–781. [PubMed: 7944869]
Loomis AL, Harvey EN, Hobart GA. Cerebral states during sleep as studied by human brain potentials. Journal of Experimental Psychology. 1937;21(2):127–144.
Lugaresi E, Coccagna G, Cirignotta F, Farneti P, Gallassi R, Di Donato G, Verucchi P. Breathing during sleep in man in normal and pathological conditions. Advances in Experimental Medicine and Biology. 1978;99:35–45. [PubMed: 696501]
Madsen PL, Holm S, Vorstrup S, Friberg L, Lassen NA, Wildschiodtz G. Human regional cerebral blood flow during rapid-eye-movement sleep. Journal of Cerebral Blood Flow Metabolism. 1991a;11(3):502–507. [PubMed: 2016359]
Madsen PL, Schmidt JF, Wildschiodtz G, Friberg L, Holm S, Vorstrup S, Lassen NA. Cerebral O2 metabolism and cerebral blood flow in humans during deep and rapid-eye-movement sleep. Journal of Applied Physiology. 1991b;70(6):2597–2601. [PubMed: 1885454]
Meijer AM, Habekothe HT, Van Den Wittenboer GL. Time in bed, quality of sleep and school functioning of children. Journal of Sleep Research. 2000;9(2):145–153. [PubMed: 10849241]
Mercer PW, Merritt SL, Cowell JM. Differences in reported sleep need among adolescents. Journal of Adolescent Health. 1998;23(5):259–263. [PubMed: 9814385]
Metcalf MG. Incidence of ovulation from the menarche to the menopause: Observations of 622 New Zealand women. The New Zealand Medical Journal. 1983;96(738):645–648. [PubMed: 6576257]
Moe KE, Prinz PN, Vitiello MV, Marks AL, Larsen LH. Healthy elderly women and men have different entrained circadian temperature rhythms. Journal of the American Geriatrics Society. 1991;39(4):383–387. [PubMed: 2010588]
Monk TH, Buysse DJ, Reynolds CF III, Kupfer DJ, Houck PR. Circadian temperature rhythms of older people. Experimental Gerontology. 1995;30(5):455–474. [PubMed: 8557094]
Morruzzi G, Magoun HW. Brain stem reticular formation and activation of the EEG. Electroencephalography and Clinical Neurophysiology. 1949;1:455–473. [PubMed: 18421835]
Moss HA, Robson KS. The relation between the amount of time infants spend at various states and the development of visual behavior. Child Development. 1970;41(2):509–517. [PubMed: 5431596]
Mulcahy D, Wright C, Sparrow J, Cunningham D, Curcher D, Purcell H, Fox K. Heart rate and blood pressure consequences of an afternoon SIESTA (Snooze-Induced Excitation of Sympathetic Triggered Activity) American Journal of Cardiology. 1993;71(7):611–614. [PubMed: 8438754]
NHLBI (National Heart, Lung, and Blood Institute). Sleep, Sleep Disorders, and Biological Rhythms: NIH Curriculum Supplement Series, Grades 9-12. Colorado Springs, CO: Biological Sciences Curriculum Study; 2003.
NLM (National Library of Medicine), NIH (National Institutes of Health). Medline Plus Online Medical Dictionary. [accessed February 6, 2006]. [Online]. Available: http://www.nlm.nih.gov/medlineplus/mplusdictionary.html.
Parker KP, Dunbar SB. Cardiac nursing. In: Woods SL, Froelicher ESS, Motzer SU, Bridges E, editors. Sleep. 5th ed. Philadelphia: Lippincott Williams and Wilkins; 2005. pp. 197–219.
Redline S, Kirchner HL, Quan SF, Gottlieb DJ, Kapur V, Newman A. The effects of age, sex, ethnicity, and sleep-disordered breathing on sleep architecture. Archives of Internal Medicine. 2004;164(4):406–418. [PubMed: 14980992]
Reynolds CF III, Kupfer DJ, Taska LS, Hoch CC, Sewitch DE, Spiker DG. Sleep of healthy seniors: A revisit. Sleep. 1985;8(1):20–29. [PubMed: 3992105]
Roffward HP, Muzio JN, Dement WC. Ontogenetic development of the human sleep-dream cycle. Science. 1966;152(3722):604–619. [PubMed: 17779492]
Sadeh A, Raviv A, Gruber R. Sleep patterns and sleep disruptions in school-age children. Developmental Psychology. 2000;36(3):291–301. [PubMed: 10830974]
Saper CB, Cano G, Scammell TE. Homeostatic, circadian, and emotional regulation of sleep. Journal of Comparitive Neurology. 2005a;493(1):92–98. [PubMed: 16254994]
Saper CB, Lu J, Chou TC, Gooley J. The hypothalamic integrator for circadian rhythms. Trends in Neuroscience. 2005b;28(3):152–157. [PubMed: 15749169]
Saper CB, Scammell TE, Lu J. Hypothalamic regulation of sleep and circadian rhythms. Nature. 2005c;437(7063):1257–1263. [PubMed: 16251950]
Sheldon SH. Sleep in infants and children. In: Lee-Choing TK, Sateia MJ, Carskadon MA, editors. Sleep Medicine. Philadelphia: Hanley and Belfus; 2002. pp. 99–103.
Simon PM, Landry SH, Leifer JC. Respiratory control during sleep. In: Lee-Chiong TK, Sateia MJ, Carskadon MA, editors. Sleep Medicine. Philadelphia: Hanley and Belfus; 2002. pp. 41–51.
Smith C, Lapp L. Increases in number of REMS and REM density in humans following an intensive learning period. Sleep. 1991;14(4):325–330. [PubMed: 1947596]
Somers V, Dyken M, Mark A, Abboud F. Sympathetic-nerve activity during sleep in normal subjects. New England Journal of Medicine. 1993;328(5):303–307. [PubMed: 8419815]
Szymusiak R. Sleep Research Society. SRS Basics of Sleep Guide. Westchester, IL: Sleep Research Society; 2005. Thermoregulation and sleep; pp. 119–126.
Tank J, Diedrich A, Hale N, Niaz FE, Furlan R, Robertson RM, Mosqueda-Garcia R. Relationship between blood pressure, sleep K-complexes, and muscle sympathetic nerve activity in humans. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology. 2003;285(1):R208–R214. [PubMed: 12793998]
Van Cauter E. Endocrine physiology. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. Philadelphia: Elsevier/Saunders; 2000. pp. 266–278.
Vitaterna M, Pinto L, Turek F. Molecular genetic basis for mammalian circadian rhythms. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier/Saunders; 2005. pp. 363–374.
Wolfson AR, Carskadon MA. Sleep schedules and daytime functioning in adolescents. Child Development. 1998;69(4):875–887. [PubMed: 9768476]
Wolfson AR, Carskadon MA, Acebo C, Seifer R, Fallone G, Labyak SE, Martin JL. Evidence for the validity of a sleep habits survey for adolescents. Sleep. 2003;26(2):213–216. [PubMed: 12683482]
Zepelin H, Siegel JM, Tobler I. Mammalian sleep. In: Kryger MH, Roth T, Dement WC, editors. Principles and Practice of Sleep Medicine. 4th ed. Philadelphia: Elsevier/Saunders; 2005. pp. 91–100.
Understanding Biological Rhythms
Among the many varieties of biological rhythm, the most well known are those relating to sleep and wakefulness, which are part of the circadian rhythm that we discuss later in this essay. Circadian, or daily, cycles are only one type of biological rhythm. Some rhythms take place on a cycle shorter than the length of a day, while others are based on a monthly or even an annual pattern.
Nor do all cycles involve sleep and wakefulness: menstruation, for instance, is a monthly cycle related to the sloughing off of the lining of the uterus, a reproductive organ found in most female mammals. Another biological rhythm is the beating of the heart, which, of course, takes place at very short intervals. Nonetheless, the circadian rhythm is the most universal of biological cycles, and it is the focus of our attention in this essay.
In discussing the operation of biological rhythms, the term biological clock often is used. A biological clock is any sort of mechanism internal to an organism that governs its biological rhythms. One such mechanism, which we examine in the next section, is the pineal gland. Internal clocks operate independently of the environment but also are affected by changes in environmental conditions.
Examples of such alterations of conditions include a decrease (or increase) in the hours of available light due to a change of seasons or a change in time alteration due to rapid travel from west to east or north to south. In the latter instance, a condition known as jet lag—increasingly familiar to humans since the advent of regular air travel in the mid-twentieth century—may ensue.
The Pineal Gland
Governing human biological cycles—the "computer" that operates our biological clocks—is the pineal gland, a cone-shaped structure about the size of a pea located deep inside the brain. At one time, the great French philosopher and mathematician René Descartes (1596-1650) held that the pineal gland was actually the seat of the soul. Though it might seem absurd now that a respected thinker would seriously attempt to locate the soul in space, as though it were a physical object, Descartes's claim resulted from hours of painstaking dissection conducted on animals.
In searching for the human soul, Descartes sought that ineffable quality described some fifteen centuries earlier by the Roman emperor and philosopher Marcus Aurelius (121-180), who wrote, "This being of mine, whatever it really is, consists of a little flesh, a little breath, and the part which governs." As it turns out, the pineal gland is, in a sense, "the part which governs": it may not be the home of the soul (which, in any case, is not a question for science), but it does govern human circadian rhythms and thus has a powerful effect on the manner in which we experience the world.
The pineal gland secretes two hormones (molecules that send signals to the body), melatonin and serotonin. During the late 1990s, melatonin became a popular over-the-counter treatment for persons afflicted with sleep disorders, because it is believed that the hormone is associated with healthful sleep. Scientists do not fully understand the role that melatonin plays in the body, although it appears that it regulates a number of diurnal, or daily, events.
In addition, melatonin seems to serve the function of controlling fat production, which is one reason why good sleep is associated not only with a healthy lifestyle but also with a healthy physique. Many health specialists maintain that for adults there is a close link between a "spare tire" (that is, fat accumulation around the waist) and stress, lack of sleep, and low melatonin levels.
Among the many roles melatonin plays in the body is its job of regulating glucose levels in the blood, which, in turn, serve to govern the production of growth hormone, or somatotropin. Growth hormone is associated with the development of lean body mass, as opposed to fat, which is why athletes involved in the Olympics and other major sporting competitions sometimes have illegally "doped" with it as a means of increasing strength. It is not surprising, then, to learn that children—who clearly need and use more growth hormone and who also need more hours of sleep than adults—also have higher melatonin levels.
Melatonin is not the only important hormone that is both secreted by the pineal gland and critical to the regulation of the body clock. Complementary to melatonin is serotonin, which is as important to waking functions as melatonin is to sleepiness. Like melatonin, serotonin serves several functions, including the regulation of attention.
Serotonin is among the substances responsible for the ability of a human with a healthily functioning brain to filter out background noise and sensory data. Thanks in part to serotonin, you are able to read this book without having your attention diverted by other sensory data around you: the voice of someone talking nearby, the sunlight or a bird singing outside, the hum of a light or a fan in the room.
By contrast, a person under the influence of the drug LSD (lysergic acid diethylamide) is not able to make those automatic filtering adjustments facilitated by serotonin. Instead, he or she is at the mercy of seemingly random intrusions of outside stimuli, such as the color of paint on a wall or the sound of music playing in the background. The secret of LSD's powerful hallucinatory effect can be attributed in part to the fact that it apparently mimics the chemistry of serotonin in the brain, "tricking" the brain into accepting the LSD itself as serotonin.
With regard to body clocks and biological rhythms, serotonin plays an even more vital governing role than does melatonin, since melatonin, in fact, is created by the chemical conversion of serotonin. On regular daily cycles the body converts serotonin to melatonin, thus influencing the organism to undergo a period of sleep. Then, as the sleeping period approaches its end, the body converts melatonin back into serotonin.