Amphetamine and the multitrial Partial Reinforcement Extinction Effect (PREE) in an operant chamber: Procedural modifications that lead to an attenuation of the PREE

The partial reinforcement extinction effect (PREE) consists of the fact that animals receiving partial reinforcement (PRF) exhibit higher resistance to extinction than animals receiving continuous reinforcement (CRF). In previous studies, we found that amphetamine (AMPH) did not affect resistance to extinction of PRF animals trained with a multitrial procedure, but abolished resistance to extinction of PRF animals trained with a 1 trial/day procedure. Based on theoretical distinctions regarding the processes underlying the development of increased resistance to extinction at short and long intertrial intervals, we suggested that AMPH disrupts the formation of a context-mediated association between stimuli associated with nonreinforcement and subsequent reinforcement. To examine further this possibility, we designed conditions in a multitrial PRF procedure that do not allow a direct association between stimuli associated with non reinforcement and reinforcement, and thus promote a context-mediated association between them. Two experiments were conducted in an operant chamber. In experiment 1, instead of the conventional 50% schedule of reinforcement throughout PRF training, days of 33% schedule of reinforcement were interspersed with days of continuous reinforcement; in experiment 2, a block (5 days) of 50% PRF schedule was alternated with a block (5 days) of CRF training, given either prior to or following PRF. In experiment 1, interspersing days of CRF training with days of 33% reinforcement schedule led to an attenuation of the PREE in AMPH-treated animals. In experiment 2, control animals that received CRF training either prior to or following PRF training exhibited a PREE similar to animals trained on PRF alone. AMPH-treated animals trained on PRF alone showed a robust PREE, but failed to exhibit PREE in both the CRF-PRF and PRF-CRF conditions. These results show that whereas amphetamine-treated animals exhibit increased resistance to extinction when trained on a multitrial PRF schedule and transferred to extinction, the drug attenuates/abolishes the effects of PRF training on extinction when such a schedule is embedded in CRF training.