The effects of rocking on the state and respiration of normal and excessive cryers.

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Abstract
The purpose of this study was to investigate the ways in which rocking affects infants'' respiration and to determine whether excessive (colicky) cryers respond as well to rocking as do normal (noncolicky) cryers, or whether they require a faster rate of rocking to soothe them. Twenty-four 42- to 56-day-old infants, 12 excessive cryers (who cried for at least 3 hours per day on at least 3 days per week), and 12 normal cryers (who never cried more than 3 hours per day) were each placed in a motorized baby carriage, rocked for 4 min after they had cried continuously for 60 s, then left in the nonrocking carriage for a further 4 min. Half the infants in each group were rocked at 40 rocks/min, the other half at 57 rocks/min. Infants cried less and had less variable respiration during rocking than during the postrock period. Their respiration entrained to the rocking, thus supporting Lester''s (1985) contention that exogenous rhythms entrain endogenous timing mechanisms, promoting soothing. More entrainment and less respiration variability was found when rocking was fast. Normal and excessive cryers did not differ in their responses to rocking, but normal cryers fussed more than excessive cryers did during the 3 min preceding continuous crying.