ACUTE EFFECTS OF CAFFEINE ON SEVERAL OPERANT BEHAVIORS IN RHESUS-MONKEYS

The acute effects of 1,3-trimethylxanthine (caffeine) were assessed us ing an operant test battery (OTB) of complex food-reinforced tasks tha t are thought to depend upon relatively specific brain functions, such as motivation to work for food (progressive ratio, PR), learning (inc remental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal res ponse differentiation, TRD), and short-term memory and attention (dela yed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). Caffeine sulfate (0.175-20.0 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in TRD percent task completed and accuracy at doses greater-than-or-equal-to 5.6 mg/kg. Caffeine produced no system atic effects on either DMTS or PR responding, but low doses tended to enhance performance in both IRA and CPR tasks. Thus, in monkeys, perfo rmance of an operant task designed to model time estimation is more se nsitive to the disruptive effects of caffeine than is performance of t he other tasks in the OTB.