Infantile Olfactory Learning

Abstract

The human fetus is exposed to the unique odor of his/her mother’s amniotic fluid while in the uterus. The odor of amniotic fluid plays two important roles related to enhanced neonatal survival. The first role is to soothe neonates, enabling them to better adapt to the world. The odor of amniotic fluid may also prevent neonates from suffering hypoglycemia and non-physiological weight loss. Hence, the olfactory memory acquired in utero helps “immature” neonate to survive. The second role of the odor of amniotic fluid is that it ensures a preparatory response for oral feeding. Sucking movements increase when infants are exposed to these odors. Infant exposure to amniotic fluid aids in the transition to colostrum/breastmilk. Neonates show preference for breasts covered with amniotic fluid and the odor induces them to suck on their own. In addition, nipple, areola, and milk odors appear equivalent to the entire breast odor in stimulating oral activity. The volatile compounds that originate from areolar secretions or breastmilk stimulate eye opening and mouth movement in newborns. This olfactory preference changes over time from amniotic fluid/colostrum to mature breastmilk. Newborn infants display behavioral attraction to the odor of amniotic fluid but this disappears by 2–5 days postpartum. Four-day-old babies whose mothers are producing transient milk rather than colostrum respond positively to the odor of their mother’s milk. Neonates learn the odors of many kinds of food through the odor of breastmilk. Mothers who abruptly change their diet after delivery – thereby lessening the degree of prenatal–postnatal olfactory continuity – experience increased difficulty establishing breastfeeding. Through these mother–infant interactions, infants ready themselves for the solids that are common in his/her community. Skin-to-skin contact immediately after birth is important not only for increasing breastfeeding duration, but also in terms of enhancing early maternal discrimination through olfactory stimuli. Mothers are also able to identify the odor of their own amniotic fluid; in this way, mother–infant bonding is strengthened through olfactory stimuli.