Infant brain responses to live face-to-face interaction with their mothers: Combining functional near-infrared spectroscopy (fNIRS) with a modified still-face paradigm

•Our very preliminary results suggest that the middle frontal cortex may underlie infant affect regulation during dyadic face-to-face interaction.•Our results also suggest that infant brain responses to maternal interaction may relate to infant temperament and mothers’ postnatal state.•Despite the exploratory nature of the current study, our findings overall support the use of fNIRS live designs to study mother-infant interaction.•Clinical application of our live design could help inform our understanding of early typical as well as atypical social-emotional development.•Future studies could help identify potential precursors/markers of risk for later psychopathology Non-invasive imaging techniques, such as fNIRS, allow us to shed light on the neural correlates of infant’s social-emotional development within the context of parent-infant interaction. On a behavioral level, numerous studies have investigated parent-infant interaction employing the still-face paradigm and found that the primary caregiver(s), often the mother, is an important coregulator of the infant’s physiological and behavioral stress response. However, limited information is available on how the infant’s brain reacts to the maternal cues during real-life interaction. Therefore, the main aim of the current study was to design a fNIRS paradigm to study live mother-infant interaction and to explore the neural correlates of infant affect regulation during real-life dyadic interaction. To this end, a modified still-face paradigm was designed, which consists of live face-to-face mother-infant, and stranger-infant, interaction episodes, including stressful, “still-face” and non-stressful, “happy-face” interaction blocks, combined with infant fNIRS imaging. Hemodynamic brain responses were collected in n = 10 (6 females, mean age 230.2 ± 17.5 days), typically developing infants using the Hitachi ETG-4000 continuous-wave system (22 channels spanning the frontal cortex; 10 Hz system sampling frequency). Infants with usable data (n = 7) showed negative activations, indicated by a decrease in oxygenated hemoglobin, over the middle frontal gyrus in response to happy-face (reunion) interaction with their mothers compared to a female stranger; suggesting deactivation of brain regions associated with affect regulation. We also explored correlations between infant brain responses to maternal interaction and infant characteristics (temperament) as well as experiential/environmental factors (mothers’ self-r