The development of social brain functions in infancy.

One fundamental question in psychology is what makes humans such intensely social beings. Probing the developmental and neural origins of our social capacities is a way of addressing this question. In the last 10 years the field of social-cognitive development has witnessed a surge in studies using neuroscience methods to elucidate the development of social information processing during infancy. While the use of electroencephalography (EEG)/event-related brain potentials (ERPs) and functional near-infrared spectroscopy (fNIRS) has revealed a great deal about the timing and localization of the cortical processes involved in early social cognition, the principles underpinning the early development of social brain functioning remain largely unexplored. Here I provide a framework that delineates the essential processes implicated in the early development of the social brain. In particular, I argue that the development of social brain functions in infancy is characterized by the following key principles: (a) self-relevance, (b) joint engagement, (c) predictability, (d) categorization, (e) discrimination, and (f) integration. For all of the proposed principles, I provide empirical examples to illustrate when in infancy they emerge. Moreover, I discuss to what extent they are in fact specifically social in nature or share properties with more domain-general developmental principles. Taken together, this article provides a conceptual integration of the existing EEG/ERPs and fNIRS work on infant social brain function and thereby offers the basis for a principle-based approach to studying the neural correlates of early social cognition.