Shift from goal-directed to habitual cocaine seeking after prolonged experience in rats.

The development of drug-seeking habits is implicated in the transition from recreational drug use to addiction. Using a drug seeking/taking chained schedule of intravenous cocaine self-administration and reward devaluation methods in rats, the present studies examined whether drug seeking that is initially goal-directed becomes habitual after prolonged drug seeking and taking. Devaluation of the outcome of the drug seeking link (i.e., the drug taking link of the chained schedule) by extinction significantly decreased drug seeking indicating that behavior is goal-directed rather than habitual. With, however, more prolonged drug experience, animals transitioned to habitual cocaine seeking. Thus, in these animals, cocaine seeking was insensitive to outcome devaluation. Moreover, when the dorsolateral striatum, an area implicated in habit learning, was transiently inactivated, outcome devaluation was effective in decreasing drug seeking indicating that responding was no longer habitual but had reverted to control by the goal-directed system. These studies provide direct evidence that cocaine seeking becomes habitual with prolonged drug experience and describe a rodent model with which to study the neural mechanisms underlying the transition from goal-directed to habitual drug seeking.