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Why do babies stop crying the moment they're scooped up into their mother's arms? A new study reveals that mouse and human babies experience an automatic calming reaction upon being carried.

Researchers say the study, published April 18 in the journal Current Biology, is the first to show that the infant calming response to carrying is a coordinated set of central, motor and cardiac regulations as well as an evolutionarily conserved component of mother-infant interactions.

The findings might also explain why calm and relaxed babies will often start crying again just as soon as they are put back down.

"From humans to mice, mammalian infants become calm and relaxed when they are carried by their mother," Kumi Kuroda of the RIKEN Brain Science Institute in Saitama, Japan said in a news release, adding that this infant response reduces the maternal burden of carrying and is beneficial for both mother and infant.

The latest findings show that a mother's embrace really is the best place for a young baby to be in terms of his or her chances of survival.  And because mothers want their babies to be calm and relaxed and because babies naturally stop crying when they are carried, the infant response is an evolutionary win-win, researchers explain.

Researchers found that when mice pups were picked up in the same way mouse mothers pick them up by the back skin very softly and swiftly, the baby mice immediately stopped moving and became compact.  

"They appeared relaxed, but not totally floppy, and kept the limbs flexed. This calming response in mice appeared similar to me to soothing by maternal carrying in human babies," Kuroda said.

Researchers also found that the heart rates of human infants and mice pups slowed down immediately when they were picked up.

Kuroda and her team say the findings have important implications for parenting and may even help prevent child abuse by helping parents see things from an infant's point of view.

"A scientific understanding of this infant response will save parents from misreading the restart of crying as the intention of the infant to control the parents, as some parenting theories-such as the 'cry it out' type of strategy-suggest," Kuroda explains. "Rather, this phenomenon should be interpreted as a natural consequence of the infant sensorimotor systems."