The purpose of this paper is to review existing behavioral and neuroendocrine perspectives on social attachment and love. Both love and social attachments function to facilitate reproduction, provide a sense of safety, and reduce anxiety or stress. Because social attachment is an essential component of love, understanding attachment formation is an important step toward identifying the neurobiological substrates of love. Studies of pair bonding in monogamous rodents, such as prairie voles, and maternal attachment in precocial ungulates offer the most accessible animal models for the study of mechanisms underlying selective social attachments and the propensity to develop social bonds. Parental behavior and sexual behavior, even in the absence of selective social behaviors, are associated with the concept of love; the analysis of reproductive behaviors, which is far more extensive than our understanding of social attachment, also suggests neuroendocrine substrates for love. A review of these literatures reveals a recurrent association between high levels of activity in the hypothalamic pituitary adrenal (HPA) axis and the subsequent expression of social behaviors and attachments. Positive social behaviors, including social bonds, may reduce HPA axis activity, while in some cases negative social interactions can have the opposite effect. Central neuropeptides, and especially oxytocin and vasopressin have been implicated both in social bonding and in the central control of the HPA axis. In prairie voles, which show clear evidence of pair bonds, oxytocin is capable of increasing positive social behaviors and both oxytocin and social interactions reduce activity in the HPA axis. Social interactions and attachment involve endocrine systems capable of decreasing HPA reactivity and modulating the autonomic nervous system, perhaps accounting for health benefits that are attributed to loving relationships.
