Differential calming responses to sucrose taste in crying infants with andwithout colic

Background. Colic is a behavioral syndrome of early infancy of unknown etio logy whose core symptom is increased crying. Both clinical anecdotal descri ptions and controlled observations converge in suggesting that a defining c haracteristic of the crying behavior is the longer duration of the crying b outs, especially during the second month of life when colic is at its peak. This implies that, once infants with colic begin crying, they do not calm as well as infants without colic. To investigate this difference objectivel y, we used response to sucrose taste as a probe of colic-normal differences in regulation of crying for three reasons. First, sucrose taste has been s hown to be a potent regulator of crying in human newborns. Second, converge nt evidence from studies in both nonhuman and human infants suggests that s ucrose calming reflects the function of central distress regulatory systems that are opioid-dependent. Third, effectiveness of sucrose calming diminis hes in normal infants by 4 to 6 weeks of age, consistent with the developme ntal increase in crying duration common to infants with and without colic. Consequently we predicted that, if the regulation of crying by sucrose tast e is relevant to the crying of infants with colic, calming responses to suc rose taste should be less effective in 6-week-old infants with colic compar ed with those without. Objectives. To investigate the clinical observation that infants with and w ithout colic differ in their ability to regulate their crying behavior, our primary objective was to determine if there were differential crying respo nses to intraoral sucrose tastes (relative to water) in crying infants with and without colic. Based on previous studies of calming responses to sucro se taste, it was predicted that sucrose-specific calming before a feeding w ould be less effective in infants with colic than in those without. A secon dary and more exploratory aim was to assess calming responses to sucrose (r elative to water) on spontaneous crying after a feed in both groups. Methods. Nineteen infants meeting modified Wessel's criteria for colic were compared with 19 age- and sex-matched normal infants without colic in a wi thin-subject controlled observation of calming and mouthing responses to bo th intraoral sucrose and water tastes. Both before and after two feedings o n the same day, each infant was observed until she or he cried continuously for 15 consecutive seconds, at which time three 250-mu L tastes of 48% suc rose solution or sterile water were administered 30 seconds apart, and infa nt responses videotaped. Outcome measures derived from second-by-second cod ing of the videorecordings were percent time crying per minute for 4 minute s and percent time mouthing per minute for 2 minutes after stimulus adminis tration. Results. As predicted, the crying of infants with colic was less affected t han the crying of infants without colic after sucrose but not water tastes before feedings. After feedings, the crying of infants with colic was less affected than the crying of infants without colic for both sucrose and wate r tastes, and sucrose was more effective than water in both groups of infan ts, These calming differences could not be attributed to differences in mou thing responses because the calming effects persisted after mouthing ceased , and there were no differences in mouthing responses between groups before or after feedings. Conclusions. As in newborns, a significant calming effect of sucrose taste that persisted beyond the cessation of mouthing could be elicited in crying 6-week-old infants, but it required a stronger taste stimulus to do so. As predicted, infants with colic were less effectively calmed by sucrose tast e than infants without. These differential effects could not be accounted f or by differences in crying when the stimulus was applied or by differences in mouthing behavior. Before a feed, these differences in calming were spe cific to sucrose taste. After a feed, infants with colic were calmed less b y both sucrose and water. These results imply that a defining individual di fference of infants with colic is that they are lets able to regulate cryin g once started and that the regulatory effects of sucrose taste are reduced in infants with colic. In light of evidence that sucrose-induced calming m ay be mediated by central opioid-dependent systems, the reduced calming eff ectiveness may be indexing a functional difference in a central opioid-depe ndent calming system in infants with colic.