 Contrary to the assumptions of the monoamine hypothesis, lowered but not heightened activity of MAO-A was associated with depressive symptoms in adolescents.This association was observed only in maltreated youth, indicating that both biological (MAO genes) and psychological (maltreatment) factors are important in the development of depressive disorders.In addition, some evidence indicates that disrupted information processing within neural networks, rather than changes in chemical balance, might underlie depression.