The stimulus-response habit-formation theory describes a transition from initial drug-consumption to compulsive drug-taking in the absence of conscious awareness (i.e., habit) (Everitt & Robbins, 2005). This is thought to occur via changes to striatonigral pathways, gradually transitioning from encoding the rewarding effects of the drug in the nucleus accumbens to encoding in the dorsal striatum (Belin & Everitt, 2008). When comparing light and heavy drinkers, cue-induced brain activation shifted from the ventral (light drinkers) to the dorsal striatum (heavy drinkers) (Vollstadt-Klein et al., 2010). Furthermore, alcoholics over-rely on habit learning rather than goal-directed actions, as demonstrated by increases in BOLD responses in the posterior putamen and decreases in the ventromedial prefrontal cortex during an instrumental learning task (Sjoerds et al., 2013).
