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. METHOD: Twenty-two healthy mothers and their infants (postnatal age 49.8 ± 17.1 days) wore actigraph monitors for seven days. Daytime (0600-2159) and nighttime (2200-0559) 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 1546 ± 107 for the mothers and 1520 ± 121 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.