Hypothesis 1 (i): Compared to placebo, mothers who receive intranasal oxytocin will show greater activation of mesocorticolimbic dopamine reward regions in the brain, including the ventral striatum and the medial prefrontal cortex, when viewing their own vs. unknown infant faces during fMRI scanning. Hypothesis 1 (ii): Compared to placebo, fathers will show greater activation of social-cognitive circuits, including the dorsal prefrontal cortex (dPFC).