How to stop your baby crying, according to science

Most parents have experienced frustration when their baby cries excessively and refuse to sleep, but new research shows the best way to soothe a crying infant is by holding and walking them for five minutes.

The evidence-based soothing strategy was presented in a paper published this week in the journal Current Biology.

"Many parents suffer from babies' nighttime crying," the paper's co-author Dr Kumi Kuroda said.

"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."

Dr Kuroda, from the RIKEN Center for Brain Science in Japan, and her colleagues have been studying the 'transport response'. This is an innate reaction seen in many mammals 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.

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Researchers compared the responses of 21 infants 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.

Data shows when the mother walked while carrying her baby, the crying infant calmed down and its heart rate slowed within 30 seconds.

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 suggested to researchers, that holding a baby alone might be insufficient in soothing crying infants, contradicting traditional assumptions that maternal holding reduces infant distress.

They determined that movement has a calming effect, and it likely activated a baby's 'transport response'.

The effect was more evident when the holding and walking motions continued for five minutes. All crying babies in the study stopped crying, and nearly half of them fell asleep.

However, when the mothers tried to put their sleepy babies to bed, more than one-third of the participants became alert again within 20 seconds.

The team found the babies produced physiological responses, including changes in heart rate, that can wake them up the second their bodies detach from their mothers.

But, 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."

Researchers recommend the parent holds their crying infant and walk with them for five minutes.

This should immediately be followed by sitting and holding infants for another five to eight minutes 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.

"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 behaviors, because they're much more complex and diverse than we thought," Dr Kuroda said.

While the experiment involved only mothers, researchers expect the effects are likely to be similar in any caregiver.