Effects of training history on drug discrimination under concurrent fixed-interval schedules.

Pigeons with previous pentobarbital-discrimination training under concurrent VI 60 VI 240 and concurrent FI 60 FI 240 schedules were trained to respond under a concurrent FI 15 FI 285 schedule of food presentation. A second group of pigeons was trained only under the concurrent FI 15 FI 285 schedule. When responding stabilized during training sessions, both groups made 75-85% of their responses on the key where responses produced the reinforcer under the FI 15 component of the concurrent schedule. When the schedule was changed to concurrent FI 150 FI 150, the presence or absence of pentobarbital continued to control responding for the group with the extensive training history, but responding by the other group was rapidly controlled by the new reinforcement schedule. These data suggest that the behavioral history of the subject can be an important determinant of stimulus control by drugs. Despite these effects of training history on drug-discrimination responding, during the first minute of the session, the dose-response curves for pentobarbital, chlordiazepoxide, ethanol, phencyclidine and methamphetamine were similar in both groups of pigeons.