Differential Calming Responses to Sucrose Taste in Crying Infants With and Without Colic
Authors: Barr Ronald G. , Young Simon N. , Wright Janice H. , Gravel Ronald , Alkawaf Rajaa 
Published: August 2004

Background.

Colic is a behavioral syndrome of early infancy of unknown etiology whose core symptom is increased crying. Both clinical anecdotal descriptions and controlled observations converge in suggesting that a defining characteristic of the crying behavior is the longer duration of the crying bouts, 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 objectively, 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 shown to be a potent regulator of crying in human newborns. Second, convergent evidence from studies in both nonhuman and human infants suggests that sucrose calming reflects the function of central distress regulatory systems that are opioid-dependent. Third, effectiveness of sucrose calming diminishes in normal infants by 4 to 6 weeks of age, consistent with the developmental increase in crying duration common to infants with and without colic. Consequently we predicted that, if the regulation of crying by sucrose taste is relevant to the crying of infants with colic, calming responses to sucrose taste should be less effective in 6-week-old infants with colic compared with those without.

Objectives.

To investigate the clinical observation that infants with and without colic differ in their ability to regulate their crying behavior, our primary objective was to determine if there were differential crying responses to intraoral sucrose tastes (relative to water) in crying infants with and without colic. Based on previous studies of calming responses to sucrose taste, it was predicted that sucrose-specific calming before a feeding would be less effective in infants with colic than in those without. A secondary and more exploratory aim was to assess calming responses to sucrose (relative 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 within-subject controlled observation of calming and mouthing responses to both intraoral sucrose and water tastes. Both before and after two feedings on the same day, each infant was observed until she or he cried continuously for 15 consecutive seconds, at which time three 250-μL tastes of 48% sucrose solution or sterile water were administered 30 seconds apart, and infant responses videotaped. Outcome measures derived from second-by-second coding of the videorecordings were percent time crying per minute for 4 minutes and percent time mouthing per minute for 2 minutes after stimulus administration.

Results.

As predicted, the crying of infants with colic was less affected than 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 water tastes, and sucrose was more effective than water in both groups of infants. These calming differences could not be attributed to differences in mouthing 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 taste than infants without. These differential effects could not be accounted for by differences in crying when the stimulus was applied or by differences in mouthing behavior. Before a feed, these differences in calming were specific to sucrose taste. After a feed, infants with colic were calmed less by both sucrose and water. These results imply that a defining individual difference of infants with colic is that they are less able to regulate crying once started and that the regulatory effects of sucrose taste are reduced in infants with colic. In light of evidence that sucrose-induced calming may be mediated by central opioid-dependent systems, the reduced calming effectiveness may be indexing a functional difference in a central opioid-dependent calming system in infants with colic.