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Carrying baby leads to comfort—from mice to people, study says

April 23, 2013
Courtesy of Cell Press
and World Science staff

There’s a good rea­son moth­ers of­ten car­ry their cry­ing ba­bies, pac­ing the floor, to help them calm down, re­search sug­gests. A study pub­lished in re­search jour­nal Cur­rent Bi­ol­o­gy on April 18 finds that both hu­man and mouse in­fants phys­ic­ally calm down up­on be­ing car­ried.

The study re­veals that this calm­ing re­flects a co­or­di­nated set of cen­tral, mo­tor, and car­di­ac events that has per­sisted across ev­o­lu­tion, the re­search­ers say. It might al­so ex­plain a frus­trat­ing real­ity for new par­ents: why calm, very young chil­dren of­ten start cry­ing again the mo­ment they’re put back down.

“From hu­mans to mice, mam­ma­li­an in­fants be­come calm and re­laxed when they are car­ried by their moth­er,” said Kumi Kuroda of the Riken Brain Sci­ence In­sti­tute in Saitama, Ja­pan, who col­la­bo­rat­ed in the work. “This in­fant re­sponse re­duces the ma­ter­nal bur­den of car­rying and is ben­e­fi­cial for both the moth­er and the in­fant.”

The idea that this very fa­mil­iar sce­nar­i­o al­so plays out in mice oc­curred to Kuroda while clean­ing the cages of her lab’s mouse col­o­ny. “When I pick­ed the pups up at the back skin very softly and swiftly as mouse moth­ers did, they 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 and her col­leagues found in tests that the heart rates of hu­man ba­bies slow im­me­di­ately up­on car­rying. Af­ter they man­aged to find mon­i­tor­ing de­vices small enough to use on con­scious mouse pups, the re­search­ers found that the same goes for mice.

They traced that re­sponse in the mice to a sense known as pro­pri­o­cep­tion, the way that in­forma­t­ion about body move­ments is per­ceived. They al­so found that spe­cif­ic parts of the brain and nerv­ous sys­tem are key to con­trol­ling the calm­ing re­sponse.

The find­ings are im­por­tant for par­ents, and may even help pre­vent some child abuse, the re­search­ers say, by help­ing grownups 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 said. “Rather, this phe­nom­e­non should be in­ter­preted as a nat­u­ral con­se­quence of the in­fant sen­sor­i­mo­tor sys­tems.”

If par­ents un­der­stand that prop­er­ly, per­haps the cry­ing will less frus­trate them, Kuroda said. And that puts those chil­dren at low­er risk of abuse.


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There’s a good reason mothers often carry their crying babies, pacing the floor, to help them calm down, research suggests. A study published in research journal Current Biology on April 18 finds that both human and mouse infants physically calm down upon being carried. The study reveals that this calming reflects a coordinated set of central, motor, and cardiac events that has persisted across evolution, the researchers say. It might also explain a frustrating reality for new parents: why calm, very young children often start crying again the moment they’re put back down. “From humans to mice, mammalian infants become calm and relaxed when they are carried by their mother,” said Kumi Kuroda of the Riken Brain Science Institute in Saitama, Japan, who collaborated in the work. “This infant response reduces the maternal burden of carrying and is beneficial for both the mother and the infant.” The idea that this very familiar scenario also plays out in mice occurred to Kuroda while cleaning the cages of her lab’s mouse colony. “When I picked the pups up at the back skin very softly and swiftly as mouse mothers did, they 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 and her colleagues found in tests that the heart rates of human babies slow immediately upon carrying. After they managed to find monitoring devices small enough to use on conscious mouse pups, the researchers found that the same goes for mice. They traced that response in the mice to a sense known as proprioception, the way that information about body movements is perceived. They also found that specific parts of the brain and nervous system are key to controlling the calming response. The findings are important for parents, and may even help prevent some child abuse, the researchers say, by helping grownups 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 said. “Rather, this phenomenon should be interpreted as a natural consequence of the infant sensorimotor systems.” If parents understand that properly, perhaps the crying will less frustrate them, Kuroda said. And that puts those children at lower risk of abuse.