Moreover, burgeoning evidence suggests that addiction to drugs (e.g., alcohol) is associated with a general bias to a habitual (also known as ‘model-free’) mode of behavior, as distinct from goal-directed (or ‘model-based’) behavior. Habitual behavior is generally associated with activity in the putamen, whereas goal-directed behavior is associated with activity in the caudate [64, 65]. Habitual behavior can also be perseverative to the extent that it can be said to be ‘out of control’. Lacking top–down executive control over habitual behavior, individuals will exhibit compulsive behaviors (e.g., compulsive alcohol intake) [66]. In our study, we further observed decreased EC from the left pre-SMA to the right putamen and from the right dACC to the right putamen. The effective strength from the left SMA to the right putamen and from the right dACC to the right putamen showed a significant negative correlation with addiction severity (AUDIT and MAST scores). More importantly, the effective strength from the right dACC to the right putamen mediated the association between addiction severity (MAST scores) and compulsive scores. These findings suggest that AUD individuals exhibit a lack of top–down control over habitual alcohol consumption-compulsive alcohol consumption, and the impairment is exacerbated by increased alcohol consumption.
