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Infant cry, sleep, and physiological regulation by transport
Nami Ohmura1 (Gianluca Esposito2, Kumi O. Kuroda1)

All babies cry. While picking up an infant is often enough to calm them, sometimes they just keep crying. Mammal infants have “Transport Response” in which become quiet and docile when they are carried. However, infants resumed crying soon after the short carrying. It was also unclear whether the carrying was more effective than other actions.
We measured the infant ECG and behaviors as mothers acted out activities commonly used to calm infants, including carrying, being pushed in a stroller, and holding while sitting. We found that 5-min walking with a crying infant not only soothes its cries but also helps it fall asleep. It was also found that if the infants stayed asleep after being laid down, their heartbeats became slower than while they were being carried. This means that sleeping infants can rest better in a bed than holding.
But about one-third of sleeping infants woke up as soon as they were placed in their beds. The analysis of ECG during laydown showed that the infants are most alerted when they are detached from the mother’s body. Furthermore, we found that the key parameter for successful laydown was the duration of the infant’s sleep before being laid down. The speed at which they were laid down or the order in which their body parts landed on the bed didn’t affect the success of putting them to sleep.
Extending this line of research could shed new light on the complex physiology of infants and could help support parents and caregivers through science-based parenting practices.

A method to soothe and promote sleep in crying infants utilizing the transport response. Ohmura N, Okuma L, Truzzi A, Shinozuka A, Saito A, Yokota S, Bizzego A, Miyazawa E, Shimizu M, Esposito G, Kuroda KO. Current Biology, 32: 1-9, 2022.

<Figure Legends>
(Top) 5-minute carrying soothes crying infant and promote sleep. Waiting 5 to 8 minutes before laydown may reduce infant awakening.
(Bottom) During laydown, sleeping infants are most alerted when they are detached from the mother’s body, not when their body touches the bed. The final maternal detachment increased the infant IBIs (decreased the infant heart rate).

1Laboratory for Affiliative Social Behavior, RIKEN Center for Brain Science, Japan
2Department of Psychology and Cognitive Science, Trent University, Italy