Maternal–infant attachment is shaped by various sensory cues, including visual, auditory, and olfactory stimuli. Infant cries evoke maternal empathy and caregiving behaviors, while infant odors activate reward-associated brain regions. However, the combined effects of these multimodal stimuli on maternal neural responses remain underexplored. This study examined how exposure to a chemically synthesized infant odor, based on compounds identified from the odor of real infants, influences maternal brain responses to infant vocalizations, specifically, pleasant (laughter) and unpleasant (crying) sounds, using functional Near-Infrared Spectroscopy (fNIRS). The odor stimulus, previously shown to elevate oxytocin levels in mothers of young children, was applied in a within-participant design across sessions held on separate days: one under the infant odor condition and the other under an odorless control condition. A total of 27 mothers of infants aged 2–11 months participated in this study. The cerebral hemodynamic response was recorded using a 56-channel fNIRS system in which participants rated the pleasantness or unpleasantness of each vocalization. Laughter elicited decreased activity in the frontopolar area under both odor conditions. However, activities in the dorsolateral prefrontal cortex (DLPFC) decreased significantly only in the odorless laughter condition, suggesting an odor-related modulation. No significant effects of infant odor were observed in the subjective ratings of the vocalizations. Generalized linear model (GLM) analyses revealed that the infant odor enhanced activation in the right superior temporal gyrus (STG) in response to crying stimuli, particularly when those cries were perceived as relatively unpleasant. In addition, mothers with lower depressive tendencies, as indicated by lower scores on the General Health Questionnaire (GHQ), exhibited moderate reductions in frontopolar activity during the infant odor-crying condition. These findings suggest that infant odor selectively enhances maternal neural sensitivity to negatively valenced infant cues, potentially promoting more adaptive caregiving responses. In mothers with fewer depressive symptoms, infant odor may also help mitigate brain activity associated with stress or anxiety elicited by infant distress. Future research should further explore the potential of infant odors to support maternal mental health and strengthen parent–infant bonding.

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