Olfactory experience mediates response to pain in preterm newborns

We assessed the effects of a familiar odor during routine blood draws in healthy preterm newborns. Infants were observed as they were undergoing either a capillary puncture on the heel (heelstick) or a venous puncture on the hand. During the procedure, one third of the infants were presented with an odor they had been familiarized with prior to the procedure, one third of the infants were presented with an odor, they had not been previously exposed to, and one third were presented with no odor. Heelsticks elicited more behavioral distress than venipunctures. Infants who were presented with a familiar odor during venipuncture showed no significant increase in crying and grimacing during the procedure compared to baseline levels. By comparison, infants presented with an unfamiliar odor or with no odor either during the heelstick or the venipuncture had a significant increase in crying and grimacing. When the pain was milder, i.e., during a venipuncture, and a familiar odor was presented, infants showed little to no crying. These results are consistent with a body of evidence on early memory and olfactory competence in fetuses and newborns.