Heritability of individual differences in cortical processing of facial affect

Facial expression of emotion is a key mechanism of non-verbal social communication in humans. Deficits in processing of facial emotion have been implicated in psychiatric disorders characterized by abnormal social behavior, such as autism and schizophrenia. Identification of genetically transmitted variability in the neural substrates of facial processing can elucidate the pathways mediating genetic influences on social behavior and provide useful endophenotypes for psychiatric genetic research. This study examined event-related brain potentials (ERPs) evoked by changes in facial expression in adolescent twins (age 12, 47 monozygotic and 51 dizygotic pairs). Facial images with happy, fearful, and neutral expressions were administered in a continuous mode, such that different expressions of the same face instantaneously replaced each other. This experimental design allowed us to isolate responses elicited by changes in emotional expression that were not confounded with responses elicited by image onset. Changes of emotional expression elicited a N240 wave with a right temporoparietal maximum and a P300 wave with a centropariatal midline maximum. Genetic analyses using a model fitting approach showed that a substantial proportion of the observed individual variation in these ERP responses can be attributed to genetic factors (36-64% for N250 and 42-62% for P300 components, respectively). This study provides the first evidence for heritability of neuroelectric indicators of face processing and suggests that ERP components sensitive to emotional expressions can potentially serve as endophenotypes for psychpathology characterized by abnormalities in social cognition and behavior.