Thus, in active cocaine abusers, the DA increases triggered by conditioned cues appear to be larger than those produced by intravenous MPH. Moreover, the DA increases triggered by the cues are associated with a desire for the drug, which suggests that conditioned responses may drive the DA signaling that triggers and maintains the motivation to take the drug. Indeed, fMRI studies of exposure to drug cues have consistently shown activation of the NAc with exposure to drug cues, which contrasts with studies in which subjects were administered cocaine and investigators reported decreases in BOLD signals in the NAc (25).
