Functional neuroimaging studies in humans and electrophysiological recordings in monkeys have suggested that the amygdala and the orbital frontal cortex play important roles in facial expression processing. To clarify the roles of these two brain regions further, this project will investigate the effects of selective damage to the amygdala or orbital frontal cortex on a monkey's ability to visually process and interpret facial expressions. First, using a newly designed task which has been validated and standardized for normal monkeys, we will determine whether lesions of the orbital frontal cortex or amygdala affect the ability of rhesus monkeys to discriminate between different facial expressions, and use infrared oculography to assess the looking patterns of the normal and lesioned monkeys to different facial expressions. Second, we will trace the development of facial expression discrimination and the pattern of looking at expressive faces in normal infants and in infants with lesions of the amygdala or orbital frontal cortex. It is hypothesized that monkeys with lesions of these areas will be impaired in their ability to discriminate between different facial expressions as compared with control animals, and that the development of these functions will be compromised in infants with lesions. Elucidating the functions of these two structures will contribute to our understanding of what goes wrong in brain disorders which affect socioemotional behavior, such as autism and schizophrenia