Runions KC, et al. - As, in meta-analyses, central nervous serotonin (5-HT) availability and aggression were identified to have a small but significant inverse relationship, but genetically-informed studies imply two pathways: one to reactive aggression, the other to proactive aggression, researchers systemically reviewed central nervous 5-HT function in children and adolescents, with attention to the function of aggression. Overall, mixed findings were noted, which provide support both for negative and positive associations of central nervous 5-HT function with aggression in children and adolescents. Problems in the conceptualization and measurement of aggression in young people, the lack of prospective designs, and the bias towards clinical samples of boys, were the propose factors that may be blurring the picture.