Influence of exteroceptive contextual conditions upon internal drug stimulus control.

Rats were trained in a spatial T-maze discrimination either in a drugged (D = pentobarbital, 17.5 mg/kg) or in a non-drugged (N = saline) state (drug discrimination learning). Either of two external discriminative stimulus sets (light vs complete darkness) was consistently associated with the D or N state. When tested in the presence of the external stimulus previously associated with training in the D state, the animals made more drug-appropriate choices when tested with low pentobarbital doses as compared to testing in the external stimulus condition previously associated with the N state. This was reflected both in the ED50 values and the slopes of the dose-generalization gradients. The gradients of the controls were intermediate to those of the experimental rats. The present data suggest a new approach for studying interactions between controlling features in environmental events and the internal state.