Amphetamine and the overtraining reversal effect.

Rats were trained in a Y-maze on a two choice simultaneous brightness discrimination with light as S+ and dark as S- (position irrelevant). Animals in the Mastery group were trained until they reached criterion and were then switched to reversal, where the reinforcement contingencies of the original training were reversed. Animals in the Overtraining group received a further 110 trials before being switched to reversal. The administration of 1 mg/kg d-amphetamine facilitated dramatically reversal learning in Mastery group. Overtraining improved reversal in saline injected animals and slowed down reversal in amphetamine-treated animals. The drug also facilitated the acquisition of the initial brightness discrimination.