Elsevier

Behavioural Brain Research

Volume 166, Issue 2, 30 January 2006, Pages 189-196
Behavioural Brain Research

Research report
Inactivation of dorsolateral striatum enhances sensitivity to changes in the action–outcome contingency in instrumental conditioning

https://doi.org/10.1016/j.bbr.2005.07.012Get rights and content

Abstract

Actions become compulsive when they are no longer controlled by their consequences. Compulsivity can be assessed using the omission procedure in which animals are required to withhold a previously reinforced action to earn reward. The current study tested the hypothesis that inactivation of the dorsolateral striatum (DLS), a structure implicated in habitual behavior, can enhance sensitivity to changes in the action–outcome contingency during omission training, thus leading to a reduction in compulsive responding. Over 10 days rats were trained to press a freely available lever for sucrose reward delivered on interval schedules of reinforcement. After learning to press the lever at a stable and high rate, rats in the omission group received a session in which the rewards were now delayed by pressing the lever; i.e. withholding lever pressing resulted in increased access to reward. A control group was yoked to the omission group and received the same number and pattern of reward delivery but without the omission contingency. Half the rats in each group received infusions of vehicle into the DLS prior to this training whereas the remainder received an infusion of the GABA-A receptor agonist muscimol. On the next day, the effect of these treatments was assessed on a probe test in which the tendency of the various groups to press the lever was assessed in extinction and without drug infusion. Rats that received vehicle infusions prior to the omission session showed complete insensitivity to the newly imposed omission contingency. In contrast, rats given the infusion of muscimol selectively reduced lever pressing compared to yoked controls. Thus, extended training with interval schedules resulted in compulsive lever pressing that prevented the learning of the omission contingency, whereas inactivation of the DLS appeared to enhance the rats’ sensitivity to this change in the action–outcome contingency.

Section snippets

Subjects and apparatus

Thirty-two naïve male Long-Evans rats weighing between 450 and 510 g were housed singly, maintained on a 14:10 h light–dark cycle, and handled daily for one week prior to surgery. Training and testing took place in 16 Med Associates (Vermont) operant chambers, each equipped with a pump with a syringe which delivered 0.1 ml of 20% sucrose solution into a recessed magazine, and a house light mounted on the wall opposite of the food magazine. Computers equipped with the MED-PC program controlled the

Placement of the implanted cannulae

Fig. 1 provides a schematic representation of the cannulae placement in the striatum. As shown in this figure, the cannulae were primarily placed in the dorsolateral region of the striatum.

Omission session behavior

The mean response rates on the last day of lever-press training are presented as the baseline in Fig. 2 (first data point in the graphs). Using treatment (muscimol and vehicle) and contingency (omission and yoked) as factors, a two-way ANOVA was conducted. No interaction between treatment and contingency was

Discussion

This study consisted of three phases: (1) lever-press training; (2) omission session after muscimol or vehicle infusion; (3) extinction test without drug infusion. Such a design aimed to assess whether DLS inactivation would affect learning during the omission session, i.e. learning about the complete reversal in instrumental contingency. As we predicted on the basis of previous work, rats given vehicle infusions were insensitive to the imposition of the omission contingency and failed to learn

Acknowledgements

This research was supported by an NSF graduate fellowship to HHY, NSF grant 9985417 to BJK and NIMH grant MH 56446 to BWB.

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