EFFECTS OF DRUGS ON RESPONSE DURATION DIFFERENTIATION .5. DIFFERENTIAL-EFFECTS UNDER TEMPORAL RESPONSE DIFFERENTIATION SCHEDULES

The effects of methamphetamine, phencyclidine and hg-tetrahydrocannabi nol on responding under temporal response differentiation schedules we re studied under three different time requirements. Under the schedule s studied, Sprague-Dawley rats were required to make a continuous resp onse for at least a minimum time duration, but not more than a maximum . Baseline performance under a temporal differentiation schedule usual ly produces a normal frequency distribution of response durations with the peak at or near the minimum duration required for delivery of the reinforcer. These frequencies were summed to calculate cumulative fre quencies that were plotted as sigmoidal curves. Under the temporal dif ferentiation 1-1.3 sec schedule, methamphetamine increased the frequen cy of short response durations at low doses, whereas high doses produc ed both long and short response durations, flattening the relative fre quency distribution. Under the temporal differentiation 4-5.2 sec and 10-13 sec schedules, methamphetamine produced only short response dura tions, which shifted the relative frequency and cumulative frequency d istribution of response durations leftward. Delta(9)-Tetrahydrocannabi nol had little effect under the temporal differentiation 1-1.3 sec and 4-5.2 sec schedules, but it greatly increased the relative frequency of short response durations under the 10-13 sec schedule. Phencyclidin e produced a similar effect under all temporal differentiation schedul es, increasing the relative frequency of short response durations. Thu s the effect of drugs on timing behavior under these temporal differen tiation schedules not only depended on the drug, but also depended on the dose and the time parameters of the schedule. These data suggest t hat drugs produce multiple effects on timing behaviors that depend on complex interactions among several factors.