As such, the present thesis does not preclude a key role for other systems associated with the addiction process, including the mesolimbic dopamine system involved in incentive salience, the dorsal striatum involved in habit formation, the parabrachial amygdala and spinothalamocortical systems involved in pain, and the prefrontal cortex involved in decision-making (Koob and Volkow 2010; George and Koob 2010). Such modules are driven by bottom-up signals from both the external world and interoceptive signals and by top-down signals from higher-order systems mediating cognitive control. Indeed, the failure of a specific module may differ from one individual to another and may represent a neuropsychobiological mechanism underlying individual differences in the vulnerability to drug addiction. For example, we have hypothesized that individual differences in the function of the incentive salience mesolimbic dopamine system and the habit/striatum modules may be particularly important for craving-type 1 (or reward craving), defined as craving for the rewarding effects of alcohol and usually induced by stimuli that have been paired with alcohol self-administration, such as environmental cues. Additionally, hypoactivity of the decision-making/prefrontal cortex module may lead to
