Approximately 20%-30% of infants cry excessively and exhibit sleep difficulties for no apparent reason, causing parental stress and even triggering impulsive child maltreatment in a small number of cases.1-8 While several sleep training methods or parental education programs may provide long-term improvement of infant cry and sleep problems, there is yet to be a conclusive recommendation for on-site behavioral interventions.9-13 Previously we have reported that brief carrying of infants transiently reduces infant cry via the transport response, a coordinated set of vagal activation and behavioral calming conserved in altricial mammals.14-18 In this study, we disentangled complex infant responses to maternal holding and transport by combining subsecond-scale, event-locked physiological analyses with dynamic mother-infant interactions. Infant cry was attenuated either by maternal carrying or by reciprocal motion provided by a moving cot, but not by maternal holding. Five-minute carrying promoted sleep for crying infants even in the daytime when these infants were usually awake, but not for non-crying infants. Maternal laydown of sleeping infants into a cot exerted bimodal effects, either interrupting or deepening the infants' sleep. During laydown, sleeping infants were alerted most consistently by the initiation of maternal detachment, then calmed after the completion of maternal detachment in a successful laydown. Finally, the sleep outcome after laydown was associated with the sleep duration before the laydown onset. These data propose a "5-min carrying, 5- to 8- min sitting" scheme for attending to infant cry and sleep difficulties, which should be further substantiated in future studies. VIDEO ABSTRACT.
Keywords: autonomic nervous system; heart rate variability; infant cry; infant reflexes; infant sleep problems; maternal behavior; mother-infant relations; parental care; parenting; transport response.
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