Newborns nurse long-term memories of smells

Within a week after birth, babies inhale new memories at their mothers’ breasts. Newborns who whiff a specific odor while breast-feeding, even if they smell it for only eight days, prefer that same odor over others a year or more later, reports a team led by physiologist Benoist Schaal of the European Center of Taste Sciences in Dijon, France.

Like other infant mammals such as rats and pigs, human newborns easily learn and remember smells associated with breast-feeding, the scientists conclude in a paper scheduled to appear in Developmental Science. These types of odor memories form most robustly during the first week after birth, the researchers propose.

Odor memories acquired during breast-feeding can be reactivated and influence behavior until at least toddlerhood, in their view.

Related research has focused on infants’ memories for food flavors, which simultaneously engage the brain’s taste and smell systems.

“These new findings add to a growing body of scientific data showing the saliency of odors for mother-infant interaction and for forming memories throughout infancy,” remarks biopsychologist Julie Mennella of the Monell Chemical Senses Center in Philadelphia.

Other recent studies suggest that babies favor odors and flavors experienced prenatally in amniotic fluid as a result of a mother’s diet, Mennella notes.

Psychologist Carolyn Rovee-Collier of Rutgers University’s Busch campus in Piscataway, N.J., calls the new findings “compelling evidence of a period of exuberant learning in early infancy when infants rapidly associate events that occur simultaneously.”

The new results support the controversial idea that infants can form associative memories, just as adults do, Rovee-Collier contends.

Schaal’s team capitalized on midwives’ practice in one part of France of recommending that nursing mothers apply a chamomile balm with an apple-like scent to their breasts to prevent nipple soreness. Researchers offered the balm to breast-feeding mothers of newborns in a French maternity ward.

Of 37 mothers who agreed to participate in the study, 20 used the chamomile concoction. They applied it after each nursing session, keeping affected areas covered with pads the rest of the time to preserve the chamomile odor. Other mothers also breast-fed but did not use the balm.

Starting one to four days after giving birth, women slathered on the aromatic balm for 8 to 120 consecutive days of nursing, as needed.

Taste and smell are linked, and chamomile does have some flavor. The researchers think, though, that the balm’s smell influenced newborns far more than anything that they tasted.

At age 7 months, children received three teething rings from an experimenter, one at a time and in random order, for one minute each. Rings had a chamomile scent, a violet scent or no scent.

Infants whose mothers had used the chamomile balm spent substantially more time mouthing and holding the chamomile ring compared with the other rings. Infants of mothers who didn’t use the balm showed no ring preferences.

At age 21 months, toddlers who had been exposed to chamomile during nursing showed little reaction when a cotton swab doused with chamomile was held under their noses. Chamomile cotton swabs elicited signs of disgust, such as nose wrinkling, from the other toddlers.

Also, toddlers formerly exposed to chamomile — whether for 8 days or longer — preferred playing with chamomile-scented toys over violent-scented or unscented toys. These toddlers almost always chose to drink from a chamomile-scented bottle rather than a violet-scented bottle. Their peers exhibited no scent-related inclinations.

Further research should explore whether components of breast milk, or even maternal contact alone, promotes lasting odor memories in newborns, Schaal says. Scientists also need to compare breast-fed to bottle-fed infants and determine whether odor memories last beyond toddlerhood.