Clinical studies have used positron emission tomography (PET) to evaluate DA’s role in drug reward and addiction (and, to a lesser extent, the role of endogenous opioids), whereas fMRI studies have concentrated on delineating the neuronal pathways affected by drugs in addicted subjects. These findings show that addiction affects not only the reward circuit, but also circuits involved with memory (conditioning/habits), motivation (energy, drive), executive function (inhibitory control, salience attribution, decision making), mood (stress reactivity and hedonic state), and interoception (internal awareness). This review focuses on the findings derived from brain-imaging studies with special attention to studies targeting DA pathways because these have been most widely investigated.
