By Andrea Hargraves 
Science has perfected the answer to soothing a crying baby: Hold it and walk it for five minutes. The evidence-based relaxation strategy arose from experiments in Japan and Italy, which were analyzed and published in Current Biology on Tuesday (13).
The authors of the research paper hope that these findings will benefit parents experiencing stress, especially those who are inexperienced.
“I raised four children,” said Komi Kuroda, lead author of the study, of the Riken Center for Brain Science in Japan, in a video. “But I myself did not expect the main results of this study until the statistical data came out,” he added.
Previously, the team studied the “transfer response” in mammals that give birth to young who cannot defend themselves, such as mice, dogs, monkeys and humans. When these animals pick up their young and start walking, the young are calm and docile, and their heart rate slows down.
Kuroda and colleagues wanted to explore this further in humans and compare the effect to other relaxing behaviors, such as rocking without walking. They recruited 21 pairs of mothers and children aged 0 to 7 months and tested them in four situations: carrying them on the go, having their mothers seated, lying in a firm bed or lying in a rocking bed.
Crying rate and heart rate decreased by 30 seconds when the babies were carried. There was a similar effect when they were swung, but not when they were held without movement. This indicates that, contrary to what might be assumed, the mother’s pregnancy was insufficient to calm the infant and the transfer response was an important factor.
Then they analyzed the effect of holding the baby for five minutes and found that the activity put 46% of them asleep and 18% fell asleep the next minute.
This showed that locking them up not only prevented them from crying, but also promoted sleep.
But with one problem: When babies were put into their cribs, more than a third were alert within 20 seconds.
Electrocardiogram readings showed that the babies’ heartbeats increased the moment they were separated from their mothers. However, when babies sleep longer before being cradled, they are less likely to wake up.
Kuroda said he was surprised by the results because he assumed other factors, such as the way or position in which they were placed in the crib, would play a more important role, but that was not the case. “Our intuition is very limited, so we need science,” he said.
Based on the overall results, they recommended a protocol to promote restful sleep: hold the child and walk with him for five minutes and then sit down and sit for another five to eight minutes before putting him to sleep.
Unlike other methods, such as letting the baby cry to sleep, this provides a comfortable environment, but more work will be needed to understand if it can adapt the infant’s sleep in the long term.