Facial skin temperature decreases in infants with joyful expression.

Studies of infant emotion rely on the assessment of expressive behavior and physiological response because infants cannot tell their feelings. Little is known about the physiological response of infants when they are in a joyful emotion. In this study, we examined changes in facial skin temperature as a physiological response, when infants are laughing, an expressive behavior of joyful emotion. Using thermography, skin temperatures of the nose, forehead and cheek were evaluated at 2-3 months, 4-6 months and 8-10 months. A decrease in facial skin temperature occurred when they laughed. The decrease was most dramatic in the nose dropping as much as 2.0 degrees C in 2 min. The response was evident in infants older than 4 months. These results suggest that a joyful emotion could be associated with a drop in facial skin temperature, which had been considered only as a sign of an unpleasant emotion. This response is developmentally controlled.