International researchers may have discovered a winning formula for soothing a crying baby, so parents preparing to embark on a long-haul flight, take note.
The team of scientists determined that holding a baby and walking with them for about five minutes is the best strategy for soothing the crying infant, based on a study that tested how different environments affect their ability to stop crying and fall asleep - the babies that is, not the parents.
The team measured the heart rates of 21 babies under four conditions: being held by their mothers as they walked; being held while seated; lying in a motionless cot; and lying in a rocking cot.
They found that when the mothers carried their babies while walking, the crying infants became docile, with their heart rates slowing within 30 seconds. A similar calming effect occurred when the infants were placed in a rocking cot, but not when the seated mothers held the babies or placed the babies in a still crib.
The researchers noted that walking with the baby had a more evident effect after about five minutes; all babies in the study stopped crying after about five minutes of being held and walked, with nearly half of them falling asleep.
Commenting on the findings, corresponding author Kumi Kuroda - a researcher specialising in affiliative social behaviour at the RIKEN Center for Brain Science in Japan - noted it's not uncommon for parents to suffer due to their child's 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," she said.
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 young and start walking, the bodies of their offspring tend to become docile as their heart rates slow.
Kuroda's team 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.
The findings suggest that holding a crying baby alone might be insufficient, contradicting the traditional assumption that maternal holding reduces an infant's distress. At the same time, movement has calming effects, likely activating a baby's transport response.
However, when the mothers tried to put their sleepy babies back to bed, more than one-third of the participants became alert again within 20 seconds. The team found all babies produced physiological responses, including changes in heart rate, that can wake them the second their bodies detach from their mothers.
The study also determined that if the infants were asleep for a longer period before being laid down, they were less likely to awaken when being put back into the cot.
"Even as a mother of four, I was very surprised to see the result. I thought babies waking up during a laydown was related to how they're put on the bed, such as their posture, or the gentleness of the movement," Kuroda said.
"But our experiment did not support these general assumptions."
While the experiment involved only mothers, Kuroda expects the effects are likely to be similar in any caregiver.
Based on their findings, the team has proposed a method for soothing and promoting sleep in crying infants. They recommend that parents:
- hold their crying infant and walk with them for five minutes
- then sit and hold the infant for a further five to eight minutes, before putting them back to bed.
The protocol, unlike other popular sleep training approaches such as letting infants cry until they tire themselves out, aims to provide an immediate solution. Whether it can improve infants' sleep in the long-term requires further research, Kuroda added.
"For many, we intuitively parent and listen to other people's advice on parenting without testing the methods with rigorous science. But we need science to understand a baby's behaviours, because they're much more complex and diverse than we thought."
This evidence-based strategy is presented in a paper published September 13 in the peer-reviewed scientific journal Current Biology.
