Any mother knows how much care a baby requires. Constant attention and care is essential for the survival and development of a baby during the first several months of their life. This is no easy chore for the parents, and infants do not hesitate to remind their mommies about their needs by loudly protesting and squirming when they are separated from their mom.
As most mothers will tell you, one of the most effective ways of calming a crying baby is by carrying them in her arms while walking. Although not a magic switch, this action usually relaxes the baby, who will stop crying and squirming. What moms do not know is why this works, or the physiological effects this soothing motion of carrying has on their baby. A recent study by Gianluca Esposito and colleagues, from the RIKEN Brain Science Institute in Japan and the University of Trento in Italy, explores the physiological mechanisms and effects, as well as the behavioural changes, caused by carrying human babies and mice pups.
Twelve healthy babies and their moms participated in the study. Esposito and his colleagues obtained video recordings of babies in their cribs, and of moms either holding their babies while sitting on a chair or while carrying their babies and walking around the room. The babies' heart rate was also recorded during this time using heart rate monitors.
Not surprisingly, the babies were more relaxed in their mother's arms than when they were left alone in their cribs. However, holding alone wasn't enough. Racing hearts slowed down, crying often stopped and fidgeting nearly disappeared when mommies walked while carrying their babies.
So, is this soothing effect of carrying an infant unique to humans? Hardly so. The researchers conducted similar experiments in mice. The researchers separated mice pups from their mothers by placing them in a clear cup where their mothers could still see them. As with human babies, the pup's heart rate decreased, ultrasonic vocalizations (thought to be the equivalent of crying in human babies) stopped and fidgeting disappeared when their mouse moms carried them with their teeth by the scruff of their neck out of the cup and back to the nest. Baby mice that had been slightly drugged or had their neck skin numbed continued squirming and vocalizing and their heart rates were still high when their moms carried them back to the nest. These results indicate that both touch and the rocking motion perceived by the infant are important factors in the soothing effect of mom's carrying. Interestingly, all the struggling and squirming prevented moms from effectively carrying their babies back to the nest, so it took them much longer to rescue their pups from the evil cup.
This study confirms what most moms have discovered through experience; carrying their baby while walking soothes their child. It appears that other baby mammals, like mice, also like being carried by their moms. In the wild, a mother might have to rescue her babies from danger and the quieting effect of carrying would aid in that rescue. For the first time, we have some insight into the physiological mechanisms of this type of mother–infant communication.