Development of synchrony between activity patterns of mother-infant pair from 4 to 18 months after birth.

Motor activities of interacting agents get temporally coordinated to form synchronized actions. Such activity synchrony is observed in several mammalian species and is supposed to play vital roles in human social interactions. Therefore, it has long been proposed that the activity patterns of mother and infant get temporally synchronized. However, few studies to date have empirically investigated the developmental course of such synchrony. The present study simultaneously measured motor activities of mother-infant pairs for about 3.5 consecutive days by actigraph, and investigated the developmental course of mother-infant synchrony. The multiple regression analysis revealed an increase of mother-infant synchrony from 4 to 18 months after birth, giving support to the notion that activity patterns of mother and infant mutually entrain each other through the course of development.