Gradients of function across the striatum. (A) Scheme depicting the striatal regions shown to be involved in goal-directed actions (A-O) and habits (S-R). DMS-dorsomedial striatum; DLS-dorsolateral striatum. (B) Representation of the striatal areas innervated by dopaminergic neurons from the VTA and the SNc in the rat. (C) The number of dendritic spines in medium spiny neurons increases in DLS and decreases in DMS after chronic exposure to methamphetamine. (D) Gradient of expression of CB1 receptors in the striatum. The references for each panel are given.

Different schedules of reinforcement produce different predisposition to habit formation in C57Bl6/J mice. (A) Acquisition of the lever pressing task in animals trained on random ratio and random interval schedules. The rate of lever pressing (per minute) for each daily session is depicted. (B) Average rate of head entry throughout training for the random interval and random ratio groups. (C) Rate of reinforcement per lever press throughout training for the random interval and random ratio groups. (D) Lever pressing during the valued versus the devalued condition for the different training schedules, normalized to the lever pressing of the last day of training. (E) Lever pressing on the training lever versus a novel lever for the different training schedules, normalized to the lever pressing of the last day of training.

Decreased predisposition for habit formation in CB1 mutant mice and in C57Bl6/J mice injected with CB1 antagonists during random interval training. (A) Acquisition of the lever pressing task in WT, CB1^+/− and CB1^−/− mice trained in a random interval schedule. The rate of lever pressing (per minute) for each daily session is depicted. (B) Normalized lever pressing during the valued versus the devalued condition for WT, CB1^+/− and CB1^−/− mice. (C) Lever pressing (normalized) on the training lever versus a novel lever in WT, CB1^+/− and CB^−/− mice. (D) Acquisition of the lever pressing task for animals injected with saline, 3 mg/kg AM251 or 6 mg/kg AM251. The rate of lever pressing (per minute) for each daily session is depicted. Note that animals were only injected during RI-30 and RI-60 training. (E) Normalized lever pressing during the valued versus the devalued condition for mice injected with saline, 3 mg/kg AM251 or 6 mg/kg AM251. (F) Lever pressing (normalized) on the training lever versus a novel lever in mice injected with saline, 3 mg/kg AM251 or 6 mg/kg AM251. The devaluation and generalization tests were performed without drug treatment.

Investigating goal-directed actions and habit formation in mice. (A) Mice were trained with two reinforcers. In the figure, the task is exemplified with one of the reinforcers, cheese, being delivered in the operant box contingent upon lever pressing, while the other reinforcer, sugar water, is being delivered freely to the mouse in the home cage. The types of reinforcers used in the figures are for illustrative purposes only. (B) Devaluation is performed in two days: Day 1, the mouse is given the reinforcer, cheese, previoulsy earned by lever pressing (devalued condition); Day 2, the mouse receives the reinforcer, sugar water, previously freely available in its home cage (valued condition). The order of the conditions is randomized. Immediately after each feeding session, which last 1 h, the mouse goes through a 5-min extinction test in the operant chamber, with the training lever extended. The number of presses on the training lever under the valued and the devalued conditions are compared. If the mouse presses more under the valued versus devalued condition, then the behavior is goal-directed behavior. However, if the mouse presses both levers equally his behavior is classified as habitual. (C) The generalization test. Two levers are presented in a 5-min extinction test: If the mouse pressed the training lever more than the novel lever, it is discriminating/exploiting. However, if the mouse presses both levers equally then there is significant generalization/exploration. Training lever is in blue and a novel lever is in pink.