In addition to the infant cry being a signal for attention, it may also be a critical component of the early formation of attachments with caregivers. We consider the complex development of that attachment, which involves reciprocal interactive signaling and a host of evolutionarily conserved caregiver factors.

In the dyadic and triadic sharing of emotions, intentions, and behaviors in families, interactive synchrony is important to the early life experiences that contribute to the development of cultural cognition. This synchrony likely depends on neurobiological circuits, currently under study with brain imaging, that involve attention, stress response, and memory.

In addition to endogenously produced opiates, which are part of normal affiliative neurocircuitry and attachment formation, exogenous opiates – such as drugs of addiction and abuse – may affect affiliation. We consider possible modulatory effects of such exogenous opiates on the development of early parent–infant attachment from both parents' and infants' perspectives.