Why do babies calm down when they are carried?

http://www.eurekalert.org/pub_releases/2013-04/r-wdb041513.php

Public release date: 18-Apr-2013
Contact: Juliette Savin
RIKEN

Parents know that crying babies usually calm down when they are picked up and carried, but why is that? In a study published today, researchers from the RIKEN Brain Science Institute show that human babies and mouse pups alike automatically and deeply relax when they are carried.

Their study, published in the journal Current Biology, is the first one to demonstrate that the infant calming response to maternal carrying is a coordinated set of nervous, motor and cardiac regulations. Kumi Kuroda and colleagues Gianluca Esposito and Sachine Yoshida, who carried out the research, propose that it might be an evolutionarily conserved, and essential, component of mother-infant interaction.

"This infant response reduces maternal burden of carrying and is beneficial for both the mother and the infant, " explains Kuroda.

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Both human and mouse babies calm down and stop moving immediately after they are carried, and mouse pups stop emitting ultrasonic cries. Mouse pups also adopt the characteristic compact posture, with limbs flexed, seen in other mammals such as cats and lions.

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"Such proper understanding of infants would reduce frustration of parents and be beneficial, because unsoothable crying is major risk factor for child abuse," says Kuroda.