Recent research has shown that genetic variations in central serotonin function are associated with biases in emotional information processing (heightened attention to signals of negative emotion) and that these biases contribute significantly to vulnerability to affective disorders. Here, we propose to examine a novel hypothesis that the biases in attention to emotional cues are ontogenetically primary, arise very early in development, and modulate an individual’s interaction with the environment during development. The four specific aims of the project are to 1) test the hypothesis that developmental processes resulting in increased functional connectivity of visual and emotion/attention-related neural systems (i.e., increased phase-synchrony of oscillatory activity) from 5 to 7 months of age are associated with the emergence of an overt attentional bias towards affectively salient facial expressions at 7 months of age, 2) use eye-tracking to ascertain that the attentional bias in 7-month-old infants reflects sensitivity to the emotional signal value of facial expressions instead of correlated non-emotional features, 3) test the hypothesis that increased serotonergic tone early in life (through genetic polymorphisms or exposure to serotonin enhancing drugs) is associated with reduced control of attention to affectively salient facial expressions and reduced temperamental emotion-regulation at 7, 24 and 48 months of age, and 4) examine the plasticity of the attentional bias towards emotional facial expressions in infancy, particularly whether the bias can be overridden by using positive reinforcers. The proposed studies will be the first to explicate the neural bases and nature of early-emerging cognitive deficits and biases that pose a risk for emotional dysfunction. As such, the results will be very important for developing intervention methods that benefit of the plasticity of the developing brain and skill formation to support healthy development.