A new look at some old mechanisms in human newborns: taste and tactile determinants of state, affect, and action.

Three studies of normal human newborns and of newborns of methadone-maintained mothers evaluated how orotactile (pacifier) and orogustatory (sucrose) stimulation, alone and in combination, affected crying behavior, heart rate, gross motor activity, eye opening, and hand-mouth coordination. For each measure of infant state, pacifier and sucrose stimulation each caused significant changes that followed very different time courses. Orotactile (pacifier) stimulation precipitated immediate changes in all behaviors, and, when the pacifier was removed, all behaviors soon reverted to baseline levels. The changes precipitated by orogustatory (sucrose) stimulation were more gradual but extended well beyond the end of sucrose administration. Although both pacifier and sucrose influences are mediated orally as opposed to in the stomach or intestine, the effects involve different brain pathways. The fact that infants born to methadone-maintained mothers did not change their behaviors during or after sucrose administration but that their reactions to pacifier stimulation could not be distinguished from those of normal infants suggests that reactions to sucrose are mediated centrally by endogenous opioids while those to the pacifier work through other central mechanisms. These findings with human newborns are consonant with those of many animal studies that have also shown rapid onset and rapid offset for contact- and suckling-induced behavioral changes, slower onset and slower offset for changes induced by taste, and opioid mediation of changes induced by the taste of sucrose. Orogustatory and orotactile influences on affect, action, and cardiovascular function are discussed from the perspectives of energetics and growth, central determinants of state, motivation, and learning during the newborn period.