EFFECT OF MULTIPLE DISCRIMINATION REVERSALS ON ACQUISITION OF A DRUG DISCRIMINATION TASK IN RATS

There are many similarities between exteroceptive stimuli and interoce ptive stimuli. Nevertheless, It has been suggested that behavior maint ained by drug stimuli might be more difficult to reverse than behavior controlled by exteroceptive stimuli. Once a discrimination is establi shed with an exteroceptive stimulus, it can be reversed by switching t he reinforcement contingencies, and repeated reversals result in progr essively 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 3.2 mg/kg phencyclidine (PCP) from salin e, in a two-lever food-reinforced operant task. After this discriminat ion was acquired, the reinforcement contingencies were reversed. A num ber of such discrimination reversals were performed to determine wheth er fewer trills would be needed to reach criterion performance with ea ch reversal. Each time the reinforcement contingencies were switched, fewer training sessions were required for the subjects to reach criter ion. These results are similar to those observed when a discrimination has been established with exteroceptive stimuli. The present study pr ovides further evidence of the similarity between interoceptive drug s timuli and exteroceptive sensory stimuli.