What's in a smile? Maternal brain responses to infant facial cues

OBJECTIVES. Our goal was to determine how a mother's brain responds to her owninfant's facial expressions, comparing happy, neutral, and sad face affect. METHODS. In an event-related functional MRI study, 28 first-time mothers were shown novel face images of their own 5- to 10-month-old infant and a matched unknown infant. Sixty unique stimuli from 6 categories (own-happy, own-neutral, own-sad, unknown-happy, unknown-neutral, and unknown-sad) were presented randomly for 2 seconds each, with a variable 2- to 6-second interstimulus interval. RESULTS. Key dopamine-associated reward-processing regions of the brain were activated when mothers viewed their own infant's face compared with an unknown infant's face. These included the ventral tegmental area/substantia nigra regions, the striatum, and frontal lobe regions involved in ( 1) emotion processing ( medial prefrontal, anterior cingulate, and insula cortex), ( 2) cognition ( dorsolateral prefrontal cortex), and ( 3) motor/behavioral outputs ( primary motor area). Happy, but not neutral or sad own-infant faces, activated nigrostriatal brain regions interconnected by dopaminergic neurons, including the substantia nigra and dorsal putamen. A region-ofinterest analysis revealed that activation in these regions was related to positive infant affect ( happy > neutral > sad) for each own - unknown infant- face contrast. CONCLUSIONS. When first-time mothers see their own infant's face, an extensive brain network seems to be activated, wherein affective and cognitive information may be integrated and directed toward motor/behavioral outputs. Dopaminergic reward-related brain regions are activated specifically in response to happy, but not sad, infant faces. Understanding how a mother responds uniquely to her own infant, when smiling or crying, may be the first step in understanding the neural basis of mother - infant attachment.