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. 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. Now, an international team of scientists led by RIKEN Center for Brain Science’s Dr. Kumi Kuroda has found that the best strategy to calm crying infants down is by holding and walking with them for 5 min.
Ohmura et al. provide a proof of concept that infant transport robustly reduces cry and potentially promotes sleep, and propose a behavioral protocol, ‘5-min carrying, 5- to 8-min sitting before bed’ for crying infants. For secure holding, caregivers should attach the infant body snugly to their own body and support the infant’s head. Five-minute walking should be on a flat and clear passage and at a steady pace, preferably without abrupt stops or turns. With these precautions, this protocol can be safely performed within the range of regular parental care. It should be noted that, unlike most behavioral interventions for infant sleep difficulties, this protocol does not address any long-term improvement of sleep regulation. This protocol instead provides an immediate calming of infant cry and may be useful especially on special occasions when the regular sleep routines, breastfeeding, or pacifiers are not effective or available. Image credit: Ohmura et al., doi: 10.1016/j.cub.2022.08.041.
“Many parents suffer from babies’ nighttime crying. That’s such a big issue, especially for inexperienced parents, that can lead to parental stress and even to infant maltreatment in a small number of cases,” said Dr. Kuroda, senior author of a paper published in the journal Current Biology.
Dr. Kuroda and her colleagues have been studying the transport response, an innate reaction seen in many altricial mammals — those whose young are immature and unable to care for themselves — such as mice, dogs, monkeys, and humans.
They observed that when these animals pick up their infants and start walking, the bodies of their young tend to become docile and their heart rates slow.
The researchers wanted to compare the effects of the transport response, the relaxed reaction while being carried, with other conditions such as motionless maternal holding or rocking and also examine if the effects persist with longer carrying in human infants.
They compared 21 infants’ responses while under four conditions: being held by their walking mothers, held by their sitting mothers, lying in a still crib, or lying in a rocking cot.
They found that when the mother walked while carrying the baby, the crying infants calmed down and their heart rates slowed within 30 sec.
A similar calming effect occurred when the infants were placed in a rocking cot, but not when the mother held the baby while sitting or placed the baby in a still crib.
This suggests that holding a baby alone might be insufficient in soothing crying infants, contradicting the traditional assumption that maternal holding reduces infant distress.
At the same time, movement has calming effects, likely activating a baby’s transport response.
The effect was more evident when the holding and walking motions continued for 5 min. All crying babies in the study stopped crying, and nearly half of them fell asleep.
But when the mothers tried to put their sleepy babies to bed, more than one-third of the participants became alert again within 20 sec.
The team found that all babies produced physiological responses, including changes in heart rate, that can wake them up the second their bodies detach from their mothers. However, if the infants were asleep for a longer period before being laid down, they were less likely to awaken during the process.
“Even as a mother of four, I was very surprised to see the result. I thought baby awoke during a laydown is related to how they’re put on the bed, such as their posture, or the gentleness of the movement,” Dr. Kuroda said.
“But our experiment did not support these general assumptions.”
Based on their findings, the authors propose a method for soothing and promoting sleep in crying infants.
They recommend that parents hold crying infants and walk with them for 5 min, followed by sitting and holding infants for another 5-8 min before putting them to bed.
The protocol, unlike other popular sleep training approaches such as letting infants cry until they fall asleep themselves, aims to provide an immediate solution for infant crying.
Whether it can improve infant sleep in the long-term requires further research.
“We are developing a ‘baby-tech’ wearable device with which parents can see the physiological states of their babies on their smartphoness in real-time,” Dr. Kuroda said.
“Like science-based fitness training, we can do science-based parenting with these advances, and hopefully help babies to sleep and reduce parental stress caused by excessive infant crying.”
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Nami Ohmura et al. A method to soothe and promote sleep in crying infants utilizing the transport response. Current Biology, published online September 13, 2022; doi: 10.1016/j.cub.2022.08.041
