Effect of multiple discrimination reversals on acquisition of a drug discrimination task in rats

There are many similarities between exteroceptive stimuli and interoceptive stimuli. Nevertheless, it has been suggested that behavior maintained by drug stimuli might be more difficult to reverse than behavior controlled by exteroceptive stimuli. Once a discrimination is established with an exteroceptive stimulus, it can be reversed by switching the reinforcement contingencies, and repeated reversals result in progressively faster relearning of the discrimination. To determine whether faster relearning of successive discrimination reversals also occurs when the discrimination is controlled by an internal drug stimulus, we trained rats to discriminate 3.2mg/kg phencyclidine-(PCP) from saline, in a two-lever food-reinforced operant task. After this discrimination was acquired, the reinforcement contingencies were reversed. A number of such discrimination reversals were performed to determine whether fewer trials would be needed to reach criterion performance with each reversal. Each time the reinforcement contingencies were switched, fewer training sessions were required for the subjects to reach criterion. These results are similar to those observed when a discrimination has been established with exteroceptive stimuli. The present study provides further evidence of the similarity between interoceptive drug stimuli and exteroceptive sensory stimuli.