Nucleus Accumbens and Ventral Tegmental Area Functional Connectivity as a Marker of Reward Sensitivity in Infancy

Early functional connectivity within the brain's reward circuitry may provide insight into the developmental origins of individual differences in pleasure and motivation. This study examined resting-state functional connectivity between two key reward-related regions, the nucleus accumbens (NAc) and ventral tegmental area (VTA), in 94 one-month-old infants (58% male; M = 4.84 weeks, SD = 0.86) and its association with later reward-related temperament. Infants completed a resting-state functional magnetic resonance imaging scan during natural sleep with a mean of 11.09 (SD = 2.78) min of retained low-motion data. Caregivers reported their infants' temperament at age six months, including high- and low-intensity pleasure as indicators of individual differences relevant to reward sensitivity. Positive resting-state functional connectivity between the NAc and VTA was present in early infancy (Cohen's d = 0.44, 95% CI [0.22, 0.65]), p < 0.001). Less positive NAc-VTA connectivity was associated with greater high-intensity pleasure at six months (β = -0.32, 95% CI [-0.54, -0.10], p = 0.004), indicating that infants with stronger connectivity between these regions exhibited less enjoyment of highly stimulating, energetic activities. NAc-VTA connectivity was not associated with low-intensity pleasure (β = -0.01, 95% CI [-0.24, 0.21], p = 0.908). These findings suggest that early variation in mesolimbic connectivity may serve as a marker of emerging individual differences in reward responsiveness, with implications for understanding affective development in infancy.