EFFECTS OF DRUGS ON RESPONSE DURATION DIFFERENTIATION .6. DIFFERENTIAL-EFFECTS UNDER TEMPORAL RESPONSE DIFFERENTIATION REINFORCEMENT OF LOWRATES OF RESPONDING SCHEDULES

The effects of methamphetamine, phencyclidine and Delta(9)-tetrahydroc annabinol on responding under differential reinforcement of low rate s chedules (DRL schedules) were studied under three different DRL time r equirements. Under the DRL schedules studied, rats were required to sp ace responses al feast a minimum, but not more than a maximum, time in terval apart. The lime intervals between responses (interresponse time s, or IRTs), when plotted as a frequency distribution, were usually a normal distribution with the peak at or near the minimum IRT required for delivery of the reinforcer, Methamphetamine flattened the IRT dist ribution and increased the frequency of long pauses under the DRL 1-1. 3 sec schedule, but shifted the IRT distribution toward shorter IRTs u nder the DRL 4-5.2 and 10-13 sec schedules, Under the DRL 1-1.3 sec sc hedule, phencyclidine also increased long pauses. Under the DRL 4-5.2 sec and 10-13 sec schedules, phencyclidine produced dual effects on th e IRT relative frequency distributions producing increases in the prop ortion of short IRTs similar to methamphetamine at low doses, but high er doses increased long pauses as well, Delta(9)-Tetrahydrocannabinol had little effect on responding under the DRL 1-1.3 sec and DRL 4-5.2 sec schedules, but it greatly increased the relative frequency of shor t IRTs under the DRL 10-13 sec schedule. Thus the effects of drugs on responding under these DRL schedules depended on the drug, the dose an d the time requirements of the schedule, which suggests that a simple description of the effects of drugs on timing behavior or time percept ion is inadequate.