Do infants show a cortisol awakening response?

Upon awakening from sleep, combined processes of deactivation of the hippocampus and activation of suprachiasmatic nucleus result in a marked increase in cortisol release from structures within the hypothalamicpituitaryadrenal axis. This phenomenon, termed the cortisol awakening response (CAR), has been studied extensively in adults. In the current study, we examine this phenomenon for the first time in infancy. Saliva samples were collected by 32 mothers from themselves and their infants (13 males; 7.817.4 months of age) at the infant's AM waking (and 30?min later), and upon waking from the infant's first nap (and 30?min later). In contrast to what has been observed with the CAR in adults, cortisol levels declined from AM waking to 30?min post-waking. Moreover, cortisol levels did not significantly rise or fall following naps. Consistent with prior research, both group-level and dyadic-level analyses showed that cortisol levels for motherinfant dyads were associated. (C) 2011 Wiley Periodicals,Inc. Dev Psychobiol 54: 736743, 2012.