The effects of morning naps, car trips, and maternal separation on adrenocortical activity in human infants
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M C Larson1, M R Gunnar, L Hertsgaard
1Institute of Child Development, University of Minnesota, Minneapolis 55455-0345.
Insights
Infant cortisol levels decrease during naps and car rides but increase with maternal separation. Stressful conditions correlate infant behavior with cortisol levels.
Area of Science:
- Developmental Psychology
- Endocrinology
- Pediatric Health
Background:
- Previous research on adrenocortical activity in infants yielded unanticipated results.
- Understanding the factors influencing cortisol levels in infants is crucial for assessing their physiological and emotional well-being.
Purpose of the Study:
- To investigate the impact of daily activities, such as napping and car rides, on salivary cortisol levels in healthy 9-month-old infants.
- To examine the effect of maternal separation versus maternal presence on infant cortisol concentrations.
- To explore the relationship between infant behavior and salivary cortisol levels under different conditions.
Main Methods:
- Three studies were conducted with healthy 9-month-old infants.
- Study 1: Measured salivary cortisol before, during, and after morning naps.
- Study 2: Assessed salivary cortisol changes during a 40-minute car ride, with and without sleep.
- Study 3: Compared salivary cortisol levels during 30 minutes of maternal separation versus 30 minutes of play with the mother present.
Main Results:
- Morning naps were associated with significant decreases in salivary cortisol, followed by a return to prenap levels.
- A 40-minute car ride significantly lowered salivary cortisol, irrespective of whether the infant slept.
- Maternal separation led to significantly higher salivary cortisol concentrations compared to play with the mother present.
- Correlations between cortisol and behavior were non-significant under non-stressful conditions.
- Distressed behavior was significantly correlated with cortisol levels during separation or stress.
Conclusions:
- Daily activities like napping and car rides can modulate infant cortisol levels.
- Maternal separation represents a significant stressor for 9-month-old infants, evidenced by elevated cortisol.
- The relationship between behavior and cortisol is context-dependent, becoming more apparent under stressful conditions.
Abstract:
3 studies of adrenocortical activity in healthy 9-month-old infants were conducted to examine unanticipated results obtained in previous research. In the first study, morning naps were examined and found to be associated with significant decreases in salivary cortisol. These decreases were followed by a significant return to prenap cortisol concentrations. In the second study, riding for 40 min in the car was also shown to significantly lower salivary cortisol concentrations. This effect was obtained both for infants who did and who did not sleep during the car trip. In the third study, the effect of 30 min of maternal separation in the laboratory on salivary cortisol was compared to the effect of 30 min of play with mother present. Separation resulted in significantly higher salivary cortisol concentrations as compared to play with mother present. In general, correlations between cortisol and behavior were found to be nonsignificant under conditions that did not produce stress elevations in cortisol, while less positive, more distressed behaviour was significantly correlated with cortisol under separation or stress conditions.