Behavioral and physiological consequences of suckling in rat and human newborns.

Suckling, in addition to yielding milk, water and calories, exerts profound behavioral effects on newborn rats and humans. In particular, suckling induces feelings of calm, reduces heart rate and metabolic rate, causes infants to bring their hands to their mouths and elevates the pain threshold. These changes are mediated by opioid and non-opioid systems, each having its own separate behavioral and neurological characteristics. The implications of suckling-induced changes for long-term motivational and cognitive change are discussed.