Does maternal care-giving behavior modulate the cortisol response to an acute stressor in 5-week-old human infants?

In previous studies, a higher quality of care-giving behavior reduced the cortisol response to acute stressors in infants aged 3 months and older. Here, we investigated whether the quality of maternal care-giving behavior affected the cortisol response to being bathed in 5-week-old infants (N = 141). Mothers and infants were observed during a bathing routine. Infant saliva samples were collected before and after bathing to assess cortisol concentrations, and the quality of maternal care-giving behavior was scored from videotapes. Bathing elicited a significant increase in infant salivary cortisol level (reactivity), and cortisol concentrations returned to pre-stressor values 40 min after bathing (recovery). In contrast, with previous findings in older infants, the quality of maternal care giving was not associated with either cortisol reactivity or recovery. This finding suggests that the quality of maternal care-giving behavior is not effective in modulating 5-week-old infants' cortisol responses to a (mild) physical stressor. Although a satisfactory neurophysiological explanation for this inference is still lacking, current knowledge of the behavioral development of very young infants supports this suggestion.