Introduction. Variability in the motivation to approach or withdraw from others displayed in infancy is thought to have long-term effects on human social development. Frontal brain asymmetry has been linked to motivational processes in infants and adults, with greater left frontal asymmetry reflecting motivation to approach and greater right frontal asymmetry reflecting motivation to withdraw. We examined the hypothesis that variability in infants’ social motivation is linked to genetic variation in the endogenous oxytocin system. Specifically, we measured infants’ frontal brain asymmetry and later looking preferences to smiling and frowning individuals and assayed a single-nucleotide polymorphism in the CD38 gene (rs3796863) linked to autism spectrum disorder and reduced peripheral oxytocin levels. Methods. 77 11-month-old infants’ (36 female) brain responses were measured via functional near-infrared spectroscopy (fNIRS) while viewing four individuals display either smiles or frowns directed toward or away from them. This was followed by a person preference test using eyetracking. Results. Frontal brain asymmetry patterns evoked by direct-gaze faces significantly differed as a function of CD38 genotype. Specifically, while non-risk A-allele carriers displayed greater left lateralization to smiling faces (approach) and greater right lateralization to frowning faces (withdrawal), infants with the CC (ASD risk) genotype displayed withdrawal from smiling faces. During eyetracking, A-allele carriers showed a heightened preference for the individual who smiled, while CC infants preferred the individual who frowned.Conclusions. Our findings demonstrate that, from early in human ontogeny, genetic variation in the oxytocin system is linked to variability in brain and behavioral markers of social motivation.
Genetic variation in the oxytocin system and its link to social motivation in human infants
