The study will elucidating the neurobiological mechanism by which genetic, environmental and social factors impinge on response inhibition. The preliminary data point to dopamine as a key neuromodulator for response inhibition. In the proposed study, we will identify the dopamine neurons, dopamine receptors and their neural substrates, and intracellular signals involved in response inhibition. This establishes a baseline to further map comprehensive neural circuits as well as cellular and molecular mechanisms.