Studies of the human infant's adrenocortical response to potentially stressful events.

Research on the regulation of the adrenocortical response in normal, healthy human infants is still quite new. The refinement of radioimmune assays to allow the measurement of cortisol in small samples of saliva, however, promises to stimulate a marked increase in work in this area over the next few years. To summarize the work to date, we can be fairly certain of the following points: (1) The adrenocortical system is responsive to stimulation at birth, and elevations can be produced by a variety of normal events, including such seemingly minor stimuli as undressing, weighing, and measuring the newborn. (2) Increases in cortisol are not always associated with behavioral distress in the infant, and at times quiescence may be the behavior associated with large elevations in cortisol. (3) At least under certain conditions, the parameters of which are as yet undetermined, the adrenocortical system of the infant appears to rapidly habituate or attenuate its response with repeated exposures to the same event. As in any new area of work, the questions left unanswered are numerous. Minimally, we can ask the following: (1) Are there stable individual differences in adrenocortical reactivity? If there are, then when do they develop, what determines these differences, and are they related to the infant's behavior or temperament? (2) Are stressors such as separation from attachment figures capable of producing large increases in cortisol (that is, a clear stress response)? If they can, then under what conditions and at what ages? (3) Finally, what are the psychological triggers of the adrenocortical stress response in human infants? While the data seem to lean toward novelty and uncertainty, the possibility that negative emotional states play a role has not been clearly ruled out. These questions and others are likely to be the focus of much of the work in this area in the near future.