The Neurobiology of Affiliation; Maternal-Infant Bonding to Life Within Social Groups

The neurobiology of affiliation is an emerging scientific field addressing the neurobiological systems and behavioral processes that sustain human social life, including both close affiliative bonds and larger social groups. Our model draws on the initial condition of mammals, whose brain is immature at birth and requires proximity to the mother's body and well-adapted caregiving for maturation of neurobiological systems that sustain social life. Three tenets of the neurobiology of affiliation are detailed: the oxytocin system, the “affiliative brain”, and biobehavioral synchrony, which supported social living across animal evolution reaching exquisite complexity in humans. The oxytocin system is implicated in plasticity at the cellular, molecular, neuronal populations, and network assembly levels; cross-talks with the stress, reward, and immune systems; and provides the neurobiological substrate for parental care and the cohesion of social groups. The “affiliative brain” defines the neural network that underpins human attachment, integrating the subcortical mammalian-general structures underpinning maternal care with higher-order systems that enable embodiment, empathy, and mentalization. Biobehavioral synchrony, an ancient mechanism that enabled small creatures to survive through coordinated action, taps the parent-infant nonverbal match by which a mature brain externally-regulates the immature brain and tunes it to social life. These components shape the environment-dependent biobehavioral envelope that charts the line from the intimacy of the parent-infant bond to life within social groups and enable complex social competencies of empathy and collaboration, resilience, and a sense of meaning.