Stress reactivity in 15-month-old infants: links with infant temperament, cognitive competence, and attachment security.

In a sample of eighty-five 15-month-old infants, salivary cortisol was obtained prior to and following a potentially stressful episode in which the child was confronted with a stranger and with a frightening robot. Infant characteristics such as anger proneness, cognitive competence, and attachment security were expected to be related to cortisol reactivity during the stressful event. The results showed higher cortisol reactivity in more anger-prone infants and in infants with higher levels of cognitive development as assessed with the Bayley Scales of Infant Development (N. Bayley, 1969). Attachment security, assessed with the Attachment Q-Set (AQS; E. Waters, 1995), was found to moderate the relation between cognitive level and cortisol reactivity; the positive relation between cognitive development and cortisol response was found in only infants with low AQS security scores. The findings may have important implications for research in the development of self-regulation in humans as well as in studies with animals.