New study explains why babies calm down when they are carried
Every parent and caregiver knows from first hand experience that babies calm down when they are picked up, gently rocked, and carried around the room. New research published in the journal Current Biology on April 18, 2013 shows that this is a universal phenomenon. Infants experience an automatic calming reaction when they are being carried, whether they are mouse pups or human babies.
"From humans to mice, mammalian infants become calm and relaxed when they are carried by their mother," says Kumi Kuroda of the RIKEN Brain Science Institute in Saitama, Japan. Being held in a mother's arms is the safest place for a baby to be, and the mother can have peace of mind knowing her baby is happy, content, and relaxed. The fact that babies are neurobiologically wired to stop crying when carried is a part of our evolutionary biology that helps our species survive.
This study (link is external) is the first to show that the infant calming response to carrying is a coordinated set of central, motor, and cardiac regulations that is an evolutionarily preserved aspect of mother-infant interactions, the researchers say. It also helps to have a scientific explanation for the frustration many new parents struggle with. . . a calm and relaxed infant will often begin crying immediately when he or she is put down. When my daughter was young, swaddling her seemed to create a compact posture and sense of security that triggered an automatic relaxation response when she was put back down and helped break this cycle.
What triggers this calming response?
Kuroda and colleagues at RIKEN determined that the calming response is mediated by the parasympathetic nervous system and a region of the brain called the cerebellum (Latin: little brain). The researchers found that the calming response was dependent on tactile inputs and proprioception. Proprioception is the ability to sense and understand body movements and keep track of your body's position in space. They also found that the parasympathetic nervous system helped lower heart rate as part of mediating the coordinated response to being carried.
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.
The idea that the familiar calming dynamic was also playing out in mice occurred to Kuroda one day when she was cleaning the cages of her mouse colony in the laboratory. She says, "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."
The Role of the Cerebellum in Calmness
As an athlete, I have written extensively about the cerebellum and its role in coordinating fine-tuned muscle movements, balance, and proprioception... The cerebellum is always on guard to protect your body from danger and prepare you for 'fight-or-flight' by keeping track of everything going on in your environment.