Rock-a-bye Baby: Biological and Social Processes Underlying Calming Effects of Babywearing
In a previous blog post, we discussed the relation between infant crying and carrying, showing that increased physical contact with infants is associated with decreased crying. Many different types of studies – from randomized control trials of skin-to-skin contact to ethnographic descriptions of care-giving in other cultures – have come to the same conclusion, lending further support to the vast benefits of wearing your baby. These findings do not entirely solve the puzzle, however, as the reason for WHY physical contact is so calming is still an open question. As with most human phenomena, there seems to be an intricate combination of biological, cultural, and psychological forces at play.
How does physical contact regulate infant distress?
Biological Mechanisms: Sensory Stimulation
In an experimental study with mouse pups, experimenters isolated the effects of physical contact from related sensations of maternal carrying. Experimenters administered local anesthesia to the part of the body in physical contact with the mother during carrying (i.e., the base of the neck where the mouse mother picks up the pup), thereby removing the effect of physical contact. When mouse pups couldn’t actually feel the sensation of tactile contact from the mother, the calming reaction – that mouse pups usually show when carried – was not demonstrated. Similarly, after temporarily disrupting the functioning of the part of the brain that controls proprioception, which allows us to feel rhythmic sensations like being rocked, being carried by the mothers also did not elicit the calming effect seen in mouse pups during normal carrying interactions. When exposing the mouse pups to visual, olfactory, or auditory stimuli, the calming effects also could not be induced. These results show that both the physical contact with the mother and the sensation of being rocked are responsible for the calming effects of carrying.
Why is touch and physical contact more calming than visual or vocal contact with caregivers?
Many people know that newborns do not arrive into the world with fully-developed eyesight and in fact, both the visual and auditory systems are still developing well into the first years of life. Given the sensitivity of the developing sensory system, inappropriate amounts of visual or auditory stimulation not only lack the ability to calm infants, but can actually interrupt sensory development and physiological processes like sleep cycles. Physical contact is the most gentle and developmentally-appropriate modality of interaction with newborn infants. In addition, babywearing in a front carrier (not forward-facing) allows infants to regulate their stimulation level by giving them a place to turn their face into the calming safety zone of the caregiver’s chest, rather than being bombarded with overwhelming amounts of visual and auditory stimulation.
Biological Mechanisms: Oxytocin
It is nearly impossible to read anything about birthing and postnatal bonding without mention of the “love drug” oxytocin. Within the context of infant-caregiver physical contact, the production of the neuropeptide oxytocin that is stimulated by skin-to-skin contact is able to increase maternal breast temperature, explaining the miraculous incubator-like effects of skin-to-skin kangaroo care (for more info, see the blog post on kangaroo care). Beyond the physiological effects, can oxytocin also provide an explanation for increased calmness and decreased crying associated with babywearing?
It is unclear whether oxytocin itself decreases crying. However, oxytocin may be mediating decreased crying through a social mechanism: increased maternal responsiveness. Oxytocin is well established in its ability to elicit maternal care and affection and has also been shown to increase patience and interactivity in fathers. Oxytocin is also specifically implicated in the neural response to infant crying.
So why would maternal responsiveness explain the calming effects of babywearing?
Social Mechanisms: Responsiveness
Responsiveness refers to the ability to respond to infants’ signals promptly and appropriately. Why is this important when trying to understand the relationship between physical contact and crying?
As outlined in a previous blog on crying and physical contact, the cultures with the lowest rates of crying have some of the highest rates of physical contact with infants. Interestingly, these proximal care cultures also exhibit another important difference in care-giving style: increased responsiveness. Specifically, adult caregivers respond more quickly – almost in an anticipatory fashion – to infants’ cues. In contrast to Western culture, responsiveness in these cultures often refers to a tendency to respond specifically to signs of distress, rather than playful bids for attention.
Experimental research has also highlighted a connection between babywearing, responsiveness, and decreased crying. In the intervention study of the effect of babywearing by Anisfeld and colleagues, mothers in the babywearing group were more responsive to infants during a play session at three months than parents in the control group.  Developmental scientists – in studies such as these – generally measure responsiveness as vocal or visual communicative responses within the context of dyadic playtime between infants and caregivers. But a closer look at the variation in responsiveness across cultures suggests that this methodological approach may be constraining our views of responsiveness. In proximal care cultures, responsiveness is not only referring to highly contingent responses to any sign of infant distress, but to a specific type of response, which is often offering the breast for nursing.
Is responsive breastfeeding one of the specific forms of responsiveness driving the decreased crying seen in proximal care cultures? Is there evidence for this from experimental studies of breastfeeding? Stay tuned! Next blog post will address the relation between mother-infant physical contact, breastfeeding, and crying.
This Guest Blog was written by Emily E. Little, M.A.
Emily is a doctoral candidate in developmental psychology at University of California, San Diego. Her dissertation research examines the social mechanisms underlying the benefits of babywearing, including how increased mother-infant physical contact facilitates higher maternal responsiveness. Her research program more broadly investigates culturally-mediated mother-infant communication, and she has collected data on early teaching in Vanuatu, infant emotional displays in Bolivia, and breastfeeding patterns in Guatemala. She is also specializing in anthropogeny, or the study of human origins, through UCSD’s Center for Academic Research and Training in Anthropogeny (CARTA), which has added an evolutionary perspective to her interests in culture, mother-infant interaction, and babywearing. She is passionate about making a positive contribution in the communities where she works, not just in San Diego – where she volunteers as a Volunteer Babywearing Educator in training with Babywearing International – but also at her international fieldsites, where she volunteers at community health centers and raises money for maternal and infant health services.
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