Mother-infant bonding is the earliest and most critical social relationship of mammalian infants, one that is promoted by an infant's innate desire to be close to his or her mother (protesting upon separation). Little is known about the mechanisms underlying these behaviors. Esposito, Yoshida and colleagues have found that both human infants and mouse pups undergo a specific relaxation response to being carried by their mothers, reducing crying, movement and heart rate.

Press Release
http://www.riken.jp/en/pr/press/2013/20130419_2/

Reference
Gianluca Esposito, Sachine Yoshida, Ryuko Ohnishi, Yousuke Tsuneoka, Maria del Carmen Rostagno, Susumu Yokota, Shota Okabe, Kazusaku Kamiya, Mikio Hoshino, Masaki Shimizu, Paola Venuti, Takefumi Kikusui, Tadafumi Kato and Kumi O. Kuroda. "Infant calming responses during maternal carrying in humans and mice". Current Biology, 2013. doi:10.1016/j.cub.2013.03.041