Behavioral state and plasma cortisol response in the human newborn

Four normal human infants were studied on 20 occasions between the first and fifteenth week of their life to assess the relation of four behavioral states (crying, quiet wakefulness, rapid eye movement, and non-rapid eye movement sleep) to plasma cortisol levels. Marked rises in plasma cortisol occurred after 20 minutes of crying. In the other behavioral states, plasma cortisol remained low and relatively constant. The pattern did not change with age, and within the limitations of this study no circadian rhythm was demonstrated. It is suggested that measurement of plasma cortisol can be as useful in psychophysiological investigations in infancy as it has proved to be in the adult.