The integrative neurobiology of affiliation. Introduction.

The research presented at this conference, including a series of excellent posters from junior investigators, documents the pervasive importance of affiliation and other social behaviors. Affiliative behaviors interact with, but are distinct from reproductive and aggressive behaviors. Patterns of social behaviors tend to be more species-typical than the behaviors associated with reproduction or aggression. However, neural circuits necessary for approach or avoidance also are necessary for the expression of various types of affiliative behavior such as maternal behavior or pair-bond formation. Furthermore, candidate neurochemical systems have been identified that contribute to various types of affiliative behavior. For example, studies revealing new behavioral functions for steroid hormones of the adrenal axis, such as corticosterone, and neuropeptides, including the endorphins, oxytocin and vasopressin, extend our general knowledge of neurobiology; they may also lead to studies that expand our understanding of social behavior and the connections to systems that regulate emotions. The work represented in this volume also has important implications for the study of serious neuropsychiatric disorders. For example, episodes of certain of these disorders can be induced by social stressors; in other disorders, a marked decrease in affiliative behaviors is a prominent feature of the patients' difficulties. Furthermore, abnormalities in animal systems implicated in the neurobiology of affiliation (oxytocin, vasopressin, and the hypothalamic-pituitary-adrenal system) have also been documented for major depression in humans. Animal models, such as those described at this conference, offer evolutionary perspectives, from which it is possible to extract general principles. At the same time, our understanding of the mechanistic and neurobiological substrates of both constructive and destructive social behaviors is increasing. At the conference, the evolutionary and mechanistic perspectives converged on the theme that studies of affiliative behaviors cannot be fully interpreted in isolation from other social behaviors; neither can they effectively be isolated from the biological and social contexts that shape their expression. Advances in this research area seem dependent on integrating experimental research across levels of analysis. Although this task is challenging, we are confident that an awareness of integrative principles can lead to new and important research opportunities.