Optimism biases denote the tendency to see future desirable events as being more likely to happen to oneself than undesirable events. Such biases are important for mental health and may extend to other individuals or social groups (social optimism biases). However, little is known as to whether social optimism biases relate to brain structure. Using sparse canonical correlation analysis, we associated cortical thickness (assessed by magnetic resonance imaging) with measures of social and personal optimism bias, trait optimism, and related concepts. We identified a defensive self-enhancement dimension that associated significantly and reliably with cortical thickness of the insula and inferior frontal cortex. This self-enhancement dimension included unfavorable biases for unpopular out-groups and indicators of personal optimism and pessimism. A shared biological substrate underlying future expectancies subserving the promotion of the self and the denigration of unpopular out-groups may render society-wide efforts to counteract stereotyping particularly difficult: such efforts may hinder the establishment of adaptive personal optimism biases.
