This chapter focuses on the modulatory role of the neuropetides in attachment as well as autonomic regulation, discussing sympathetic and parasympathetic arousal, particularly dorsal vagal and ventral vagal regulation as suggested by polyvagal theory. The probable role of the endogenous opioid system in the modulation of oxytocin and vasopressin release is discussed with a view toward the elicitation of both relational and active defensive responses are reviewed. Porges’ Polyvagal Theory delineates two parasympathetic medullary systems, the ventral and dorsal vagal. Brain circuits involved in the maintenance of affiliative behavior are precisely those most richly endowed with opioid receptors. Avoidant attachment is commonly associated with parental figures that have been rejecting or unavailable and refers to a pattern of attachment where the child avoids contact with the parent. The similarity of severe posttraumatic presentations to autism suggests that the research with regard to social affiliation in autism spectrum.