title: Mother-infant activity synchrony as a correlate of the emergence of circadian rhythm.
abstract: OBJECTIVE
  Entrainment to the day-night cycle is critical for infant sleep and social development. Synchronization of infant circadian systems with the social 24-hr day may require maternal activity signals as an entraining cue. This descriptive and exploratory research examines the activity level and circadian pattern in mothers and infants.
  
  
  METHODS
  Twenty-two healthy mothers and their infants (postnatal age 49.8 ± 17.1 days) wore actigraph monitors for seven days. Daytime (06:00-21:59) and nighttime (22:00-05:59) activity levels and circadian parameters of rest-activity patterns (i.e., mesor, amplitude, acrophase, and 24-hr cosinor fit) were calculated.
  
  
  RESULTS
  Mothers and infants were significantly more active during the day than at night. The goodness-of-fit index for the model (R2) indicates that circadian rhythm accounted for a mean of 29 ± 10% and 12 ± 8% of the variability in maternal and infant activity, respectively. Acrophase of activity occurred at 15:46 ± 1:07 for the mothers and 15:20 ± 1:21 for the infants. The mean within-dyad correlation of activity counts was r = .46 ± .11, and the within-dyad correlation was associated with the amplitude (r = .66, p < .01) and 24-hr cosinor fit of infant activity (r = .67, p < .01).
  
  
  CONCLUSIONS
  Our findings suggest maternal rhythms as a possible exogenous influence on shaping an infant's emerging rhythms and synchronizing them with the external light-dark cycle. Strong pattern synchrony between maternal and infant activity may support infant circadian entrainment and enhance a regular 24-hr sleep-wake schedule during the early postnatal weeks.
authors.affiliation: Department of Nursing, College of Medicine, National Taiwan University, No. 1 Sec. 1 Jen-Ai Rd., Taipei, Taiwan. stsai@ntu.edu.tw
authors.forename: Shao-Yu
authors.initials: SY
authors.lastname: Tsai
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Barnard
authors.forename: Martha J
authors.initials: MJ
authors.lastname: Lentz
authors.forename: Karen A
authors.initials: KA
authors.lastname: Thomas
mesh_terms: D056044:Actigraphy; D000328:Adult; D000339:Affect / Q000502:physiology; D002657:Child Development / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009034:Mother-Child Relations; D009035:Mothers / Q000523:psychology; D009043:Motor Activity / Q000502:physiology; D002666:Psychology, Child; D012146:Rest / Q000502:physiology; D012890:Sleep / Q000502:physiology*; D013315:Stress, Psychological / Q000503:physiopathology