TOKYO — It’s a situation just about every new parent has faced: After falling into a deep slumber, the baby wakes up and won’t stop crying. Even being held, swaddled, and sung to doesn’t seem to calm the infant down. Now, scientists in Japan say they have finally figured out the secret to success. A five minute walk, followed by cuddling in a chair is the key to getting a crying baby back to sleep, according to new research.
Holding and carrying them works better than a simple cuddle, offering a cost-free and effective technique, study authors say. It causes physiological changes, including slowing heart rate. The study recommends the advice should be given to all parents.
Researchers are now developing an app based on the findings, which will alert parents if they need to pick their baby up.
“Many parents suffer from babies’ night time crying,” explains lead author Dr. Kumi Kuroda, of the RIKEN Center for Brain Science, in a statement. “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.”
‘Transport response’ seen in animals carries over to humans, too
Most parents know the occasional frustration and discomfort of dealing with a crying baby. For some, it’s a regular occurrence that affects the baby’s ability to sleep and stresses out the parents. Dr. Kuroda and colleagues identified a “transport response” in distressed mouse pups and human infants in which they calm down when carried by their mothers.
The phenomenon, also seen in dogs and monkeys, is a complex series of parallel biological processes. It helps parents move babies. Researchers 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.
In experiments involving 21 infants, changes in heart rate and behavior were compared as their mothers carried out activities. These included carrying, being pushed in stroller and holding while sitting. The babies wore EEG (electroencephalogram) skull caps. Small discs measure electrical activity. Data were recorded when they were crying, calm, awake or asleep.
When the mother walked while carrying the baby, crying infants calmed down and their heart rates slowed within 30 seconds. A similar calming effect occurred when they were placed in a rocking cot, but not when they were placed in a crib or the mother held them while sitting. It suggests holding a baby alone is insufficient to soothe a crying infant, contradicting the traditional assumption.
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 five minutes. All babies stopped crying, and nearly half of them fell asleep. But when the mothers tried to put their sleepy babies to bed, more than a third became alert again within 20 seconds.
The team found 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, the team found.
“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 are put on the bed, such as their posture, or the gentleness of the movement,” says Dr. Kuroda. “But our experiment did not support these general assumptions.”
Dr. Kuroda expects the effects are likely to be similar in fathers and any other caregivers. “Walking for five minutes promoted sleep, but only for crying infants. Surprisingly, this effect was absent when babies were already calm beforehand,” she adds.
‘Science-based parenting’ is the way to go for getting a crying baby back to sleep
Monitoring heartbeat also enabled dissection of the effect of each activity as infants were handled. It showed babies were extremely sensitive to all movements. For example, heart rates went up when mothers turned or when they stopped walking. The most significant event that disturbed sleep happened just when infants became separated.
Every mother has experienced the disappointment of having a finally sleeping baby wake up again after being put down. The analysis pinpoints the problem. “Although we did not predict it, the key parameter for successful laydown of sleeping infants was the latency from sleep onset,” says Dr. Kuroda.
Babies often woke up if they were put down before they got about eight minutes of sleep. Based on the findings, Dr. Kuroda recommends mothers should carry crying babies steadily for about five minutes with few abrupt movements. This should be followed by about eight minutes of sitting, before laying them down for sleep.
The study, published in the journal Current Biology. did not address why some babies cry excessively and cannot sleep. But it offers an immediate solution that can help parents of newborns. Additionally, the researchers recognize the usefulness of heart rate data in this age of wearable fitness devices.
“We are developing a ‘baby-tech’ wearable device with which parents can see the physiological states of their babies on their smartphones in real-time,” says Dr. Kuroda. “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.”
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, says Dr. Kuroda. “For many, we intuitively parent and listen to other people’s advice on parenting without testing the methods with rigorous science,” she adds. “But we need science to understand a baby’s behaviors, because they’re much more complex and diverse than we thought.”
Infant sleep training expert Jayne Havens, who was not involved in the research, tells StudyFinds that Kuroda’s strategy certainly has merit, but it’s more akin to a Band-Aid than a cure-all. “While these findings are accurate, if you assist babies into a deep sleep by holding them, walking with them, and sitting with them until they are deeply asleep, it’s highly probable that they will wake 30-40 minutes later crying for help to get back to sleep,” says Havens, owner and founder of The Center for Pediatric Sleep Management in Baltimore.
“The REAL secret to babies sleeping in longer stretches is to teach them to fall asleep independently,” she adds. “When a baby can fall asleep without the walking, the rocking, the sitting etc., they are better positioned to fall back asleep without help when they briefly rouse between sleep cycles.”
South West News Service writer Mark Waghorn contributed to this report.