Although the infant-caregiver attachment bond is critical to survival, little is known about the biological mechanisms supporting attachment representations in humans. Oxytocin plays a key role in attachment bond formation and maintenance in animals and thus could be expected to affect attachment representations in humans.To investigate this possibility, we administered 24 IU intranasal oxytocin to healthy male adults in a double-blind, placebo-controlled, crossover designed study and then assessed memories of childhood maternal care and closeness-two features of the attachment bond. We found that the effects of oxytocin were moderated by the attachment representations people possess, with less anxiously attached individuals remembering their mother as more caring and close after oxytocin (vs. placebo) but more anxiously attached individuals remembering their mother as less caring and close after oxytocin (vs. placebo). These data contrast with the popular notion that oxytocin has broad positive effects on social perception and are more consistent with the animal literature, which emphasizes oxytocin's role in encoding social memories and linking those memories to the reward value of the social stimulus.neurohypophyseal hormones | social cognition | social memory | individual differences | Syntocinon A ccording to attachment theory (1-3), infants develop affective bonds with their caregivers, which arise from an attachment behavioral system that promotes the infant's survival by facilitating caregiver closeness and protection. A core feature of the attachment system is the notion of internal working models, which are thought to contain information about close others' reliability and availability to meet one's needs for security, as well as affective and motivational information about regulating the self in relation to significant others. These attachment representations are formed in the infant-caregiver relationship but continue to operate throughout the lifespan and are adjusted to incorporate new close relationship experiences. The attachment behavioral system plays an important role in guiding interpersonal perceptions, expectations, and behaviors, but it is also significant from an evolutionary perspective-the attachment bond is thought to be essential for species survival because it fosters caregiver protection, thereby allowing the infant to survive to maturity and reproduce (2). Although critical to survival, little is known about the biological mechanisms supporting attachment representations in humans.One candidate suggested by animal research is oxytocin, a mammalian hormone that acts as a neuromodulator in the brain. Oxytocin is produced in the hypothalamus and released into the circulatory system, where it is involved in facilitating uterine contractions during parturition and milk ejection during lactation (4). Oxytocin also is released directly into the brain, where it has been shown to play a critical role in attachment bond formation and maintenance in animals (5-8). A working hypothesis is that...