title: Age-related changes in the circadian modulation of sleep-spindle frequency during nap sleep.
abstract: OBJECTIVE
  Sleep spindles exhibit a clear circadian modulation in healthy younger people. During the biological night (when melatonin is secreted), spindle density and spindle amplitude are high and spindle frequency and its variability are low, as compared with the biological day. We investigated whether this circadian modulation of spindle characteristics changes with age.
  
  
  METHODS
  A 40-hour multiple-nap paradigm under constant-routine conditions
  
  
  METHODS
  Chronobiology Laboratory, University Psychiatric Hospitals, Basel, Switzerland
  
  
  METHODS
  Seventeen younger (20-31 years) and 15 older (57-74 years) volunteers.
  
  
  METHODS
  N/A.
  
  
  RESULTS
  Whereas the circadian modulation of spindle density, amplitude, duration, and intraspindle frequency variability was not greatly affected by age, we found significant changes in the circadian modulation of spindle frequency. The pronounced circadian modulation of spindle frequency in younger, but not older, subjects was phase locked with the circadian rhythm in melatonin secretion. In the latter, circadian modulation was attenuated and tended to be advanced with respect to the timing of melatonin secretion. There was no difference between age groups in the phase of the sleep-wake cycle or that of melatonin, nor did the phase angle between them differ. Although changes in the circadian modulation of spindle frequency in older subjects were accompanied by reduced amplitude in the sleep consolidation profile, there was no significant correlation between spindle frequency and sleep consolidation.
  
  
  CONCLUSIONS
  This multiple-nap protocol under constant-routine conditions revealed an age-dependent weaker coupling of the circadian rhythms of spindle frequency and sleep propensity to the circadian rhythm of melatonin secretion.
authors.affiliation: Centre for Chronobiology, Psychiatric University Hospitals, Wilhelm-Kleinstr, Basel, Switzerland.
authors.forename: Vera
authors.initials: V
authors.lastname: Knoblauch
authors.forename: Mirjam
authors.initials: M
authors.lastname: Münch
authors.forename: Katharina
authors.initials: K
authors.lastname: Blatter
authors.forename: Wim L J
authors.initials: WL
authors.lastname: Martens
authors.forename: Carmen
authors.initials: C
authors.lastname: Schröder
authors.forename: Corina
authors.initials: C
authors.lastname: Schnitzler
authors.forename: Anna
authors.initials: A
authors.lastname: Wirz-Justice
authors.forename: Christian
authors.initials: C
authors.lastname: Cajochen
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000378:metabolism; D008875:Middle Aged; D017286:Polysomnography; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology
chemical_list: D008550:Melatonin