Rapid dopamine release in the core of the NAc, as measured with fast scan cyclic voltammetry, is observed during presentation of an audiovisual CS associated with cocaine infusion during self-administration sessions. Top, dopamine concentration significantly increased relative to CS (tone houselight) onset at time 0 in animals well-trained to self-administer the drug. Bottom, the same tone houselight stimulus did not evoke dopamine release in animals without a history of cocaine self-administration. Dopamine concentration changes are presented as means (solid line) and standard deviation of the mean (dashed line). Duration of tone houselight CS is indicated by blue line (20 s total). Figure from Nature (Phillips and others, 2003, 422:614–618).