title: The development of circadian rhythms in a human infant.
abstract: OBJECTIVE
  This study examines the ontogeny and interaction of circadian rhythms of sleep, wake, temperature, melatonin, and feeding in the human newborn, and the influence of photic and non-photic factors on the initiation of entrainment.
  
  
  METHODS
  An infant's sleep-wake state, temperature, and salivary melatonin were monitored from birth to 6 months. Temperature was obtained every hour, and the infant's sleep/eating onset/termination were observed continuously and recorded until day 182. Salivary melatonin was obtained weekly for a 24-hour period, starting at week 3.
  
  
  METHODS
  The infant slept in his parents' bedroom. All household members awakened, retired, and ate meals according to a fixed schedule during the study, while the infant ate, slept, and woke on demand.
  
  
  METHODS
  A healthy male infant was the subject. Biological parents gathered data continuously for six months.
  
  
  METHODS
  The infant's schedule was on-demand; the household's was fixed. Illumination was restricted to sunlight.
  
  
  RESULTS
  The circadian rhythm of temperature appeared first, soon after birth, and became statistically significant within one week. The wake circadian rhythm appeared second, attaining significance at day 45; approximately the same time that increased melatonin concentration began to occur at sunset. The sleep circadian rhythm appeared last, attaining significance after day 56. Ninety to 120 minute zones of sustained wakefulness first appeared in the second month of life subsequent to awakening and prior to sleep onset. The infant's nocturnal sleep-onset was coupled to sunset before day 60 and subsequently to family bedtime, giving evidence of initial photic entrainment followed by social entrainment.
  
  
  CONCLUSIONS
  Circadian rhythms appeared much more rapidly in this infant than previously reported; their rapid appearance was probably facilitated by maximal exposure to sunlight, and regular social cues. These lighting conditions replicate universal infant experience prior to the invention of artificial light.
authors.affiliation: University of Texas Southwestern Medical Center at Dallas, USA.
authors.forename: K
authors.initials: K
authors.lastname: McGraw
authors.forename: R
authors.initials: R
authors.lastname: Hoffmann
authors.forename: C
authors.initials: C
authors.lastname: Harker
authors.forename: J H
authors.initials: JH
authors.lastname: Herman
mesh_terms: D001921:Brain / Q000378:metabolism / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D007223:Infant; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism; D012890:Sleep / Q000502:physiology*
chemical_list: D008550:Melatonin