Animal Models of the Preoccupation/Anticipation Stage of the Addiction Cycle
Second-Order Schedules of Reinforcement
Second-order schedules of reinforcement involve training animals to work for a previously neutral stimulus that ultimately predicts drug availability. These schedules maintain high rates of responding (e.g., up to thousands of responses per session in monkeys) and can motivate the animal to emit extended sequences of behavior before any drug is administered. Such extended schedules minimize potentially disruptive, nonspecific, acute drug and treatment effects on response rates. High response rates are maintained even for doses that decrease rates of responding on a regular fixed-ratio schedule, indicating that performance on the second-order schedule is unaffected by the acute effects of the drug that would otherwise disrupt operant responding. The maintenance of performance under second-order schedules with drug-paired stimuli appears to be analogous to the maintenance and reinstatement of drug seeking behavior in humans who are also presented with drug-paired stimuli.