Differences between Japanese infants and Caucasian American infants in behavioral and cortisol response to inoculation.

The behavioral and cortisol responses of Japanese infants and Caucasian American infants, 4 months of age, were observed during and following routine inoculation. The Caucasian American group showed a more intense initial affective response and a longer latency to quiet than the Japanese group; the Japanese group showed a greater cortisol response. A 4-group taxonomy was created based on high or low behavioral and cortisol response: high behavior-high cortisol, low behavior-low cortisol, high behavior-low cortisol, and low behavior--high cortisol. There were significant differences between the 2 groups of infants using this taxonomy: Infants in the Caucasian American group were more likely to fall in the high behavior-low cortisol group, while infants in the Japanese group were more likely to fall in the low behavior-high cortisol group.