According to models of addiction, the main brain regions underlying addiction make up a network of, at a minimum, four interdependent and overlapping circuits (Baler and Volkow, 2006): (i) reward, involving the nucleus accumbens and ventral pallidum (ii) memory and learning, including the amygdala and hippocampus; (iii) cognitive control, located in the prefrontal cortex and dorsal anterior cingulate cortex; and (iv) motivation and/or drive and salience evaluation, located in the orbital frontal cortex. In addition, amygdala and ventral/rostral anterior cingulate cortex (including subgenual area), regions that are associated with craving and emotional regulation, are also likely to affect the reactivity of the above circuits and parts of this network (Bechara, 2005; Bush et al., 2000; Volkow et al., 2005). These regions are modulated by dopamine and interconnected mostly through glutamatergic and GABA-ergic projections. The interactions between these regions are integrated to generate the behavioral output toward a reinforcing stimulus (O'Doherty, 2004), such that addictive drugs intensely activate the reward and motivation circuits, usurp systems underlying reward-related learning and memory, and hijack cognitive control resources (Baler and Volkow, 2006; Bechara, 2005;
