What's in a Smile? Maternal Brain Responses to Infant Facial Cues

TLDR

The neural basis of mother‑infant attachment may be illuminated by studying how mothers uniquely respond to their own infant’s facial expressions. The study aimed to determine how mothers’ brains respond to their own infant’s happy, neutral, and sad facial expressions. Using event‑related fMRI, 28 first‑time mothers viewed 60 randomized 2‑second stimuli of their own and unknown infants’ happy, neutral, and sad faces with variable interstimulus intervals. Viewing their own infant’s face, especially happy expressions, robustly activated dopaminergic reward regions (ventral tegmental area/substantia nigra, striatum) and associated frontal, motor, and cognitive areas, with activation magnitude scaling with positive affect (happy > neutral > sad).

Abstract

Our goal was to determine how a mother's brain responds to her own infant's facial expressions, comparing happy, neutral, and sad face affect.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.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-of-interest analysis revealed that activation in these regions was related to positive infant affect (happy > neutral > sad) for each own-unknown infant-face contrast.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.