Classical conditioning in newborn humans 2–48 hours of age

Abstract

Classical conditioning was studied in newborn humans 2–48 hours of age. Infants in the Experimental group received 18, 2-min conditioning trials, each consisting of 10 s of gentle forehead stroking followed immediately by midline intraoral delivery of 0.2 ml 12.5% (0.037 M) sucrose solution via pipette. Sucrose delivery for infants in one control group was delayed following stroking by intervals of 10, 20, or 30 s presented randomly. Infants in the second control group were not stroked but only received sucrose on each trial. Immediately following the 18 sucrose trials, all infants received 9, 1-min extinction trials which consisted exclusively of 10 s of forehead stroking with no other manipulations during the remaining 50 s. All sessions were video-recorded and analyzed at a later date, with special attention paid to head-orienting, sucking, and crying behaviors. Only infants in the Experimental group presented evidence for classical conditioning. Relative to infants in the first control group, they emitted many more head-orient and sucking responses during the 10-s stroking intervals. Moreover, they exhibited a classic extinction function to stroking in sucrose absence. Finally, 7 of 8 Experimental infants cried during extinction, whereas only 1 of 16 Control infants cried. These findings demonstrate the ability of human newborn infants to extract predictability between two related events and that this form of conditioning is strongly affective. Implications for early mother-infant bond development are discussed.