Maternal odor shapes rapid face categorization in the infant brain.

To successfully interact with a rich and ambiguous visual environment, the human brain learns to differentiate visual stimuli and to produce the same response to subsets of these stimuli despite their physical difference. Although this visual categorization function is traditionally investigated from a unisensory perspective, its early development is inherently constrained by multisensory inputs. In particular, an early-maturing sensory system such as olfaction is ideally suited to support the immature visual system in infancy by providing stability and familiarity to a rapidly changing visual environment. Here, we test the hypothesis that rapid visual categorization of salient visual signals for the young infant brain, human faces, is shaped by another highly relevant human-related input from the olfactory system, the mother's body odor. We observe that a right-hemispheric neural signature of single-glance face categorization from natural images is significantly enhanced in the maternal versus a control odor context in individual 4-month-old infant brains. A lack of difference between odor conditions for the common brain response elicited by both face and non-face images rules out a mere enhancement of arousal or visual attention in the maternal odor context. These observations show that face-selective neural activity in infancy is mediated by the presence of a (maternal) body odor, providing strong support for multisensory inputs driving category acquisition in the developing human brain and having important implications for our understanding of human perceptual development.