Predicting Positive Affect in Infancy

Positive affect (PA) is integral to health and development, yet its early origins remain largely unexplored. In this pre-registered study (N = 78), we investigated whether infant-specific biological and social-behavioral factors predict PA in early development. Seventy-eight typically developing infants and their mothers from a longitudinal cohort contributed complete data. At 5 months, infant CD38 rs3796863 genotype (linked to oxytocin release), salivary cortisol levels, and social engagement during mother-infant free play were assessed. At 7 months, infant PA was measured using the Positive Emotionality/Surgency (PEm) factor of the Infant Behavior Questionnaire-Revised (IBQ-R, operationalizing PA as a broader PEm temperament construct). Analysis revealed that infant PA at 7 months was predicted by infant CD38 genotype, with AA/AC genotypes associated with higher PA; lower infant cortisol levels; and higher infant social engagement. These infant-specific factors collectively explained 27% of the variance in infant PA. Corresponding maternal biological and behavioral measures did not predict infant PA. These findings offer novel insights into the early, multifaceted, and infant-specific biological and behavioral foundations of PA, a crucial component of human well-being. SUMMARY: Infant CD38 genotype, cortisol, and social engagement at 5 months predict positive affect at 7 months Infant-specific biological and behavioral factors account for 27% of variance in positive affect Maternal measures of the same variables did not predict infant positive affect Pre-registered analysis validates infant-centric model of early affective development.