On habits and addiction: An associative analysis of compulsive drug seeking.

The processes that underlie the pathological pursuit of drugs in addiction and that support the transition from casual drug taking to their compulsive pursuit have recently been proposed to reflect the interaction of two action control processes that mediate the goal-directed and habitual control of actions for natural rewards. Here we describe the evidence for these learning processes, their associate structure and the motivational mechanisms through which their operation is translated into performance. Finally, we describe the potential changes in the interaction between habitual and goal-directed processes induced by drug addiction that subserve compulsive drug pursuit; i.e. the increase in habit learning and reduction in the regulation of habits induced by changes in the circuitry that mediates goal-directed action.