Abstract
20 rats were trained to bar press for sucrose solution in the presence of one of two stimulus conditions. On each of 6 daily training sessions the reward value of the stimuli was reversed. 20 min. prior to the second reversal, the subjects received an i.p. injection of either isotonic saline, 2 mg/kg, 4 mg/kg, or 8 mg/kg of methylphenidate. The performance of drugged subjects was superior on Reversal 2. In the 2 mg/kg condition this effect persisted over Reversals 2 to 6, indicating that more than a transient performance effect was induced by drug administration. A second study using 16 subjects was conducted to ascertain additional information relative to the effects of the 2 mg/kg dose on short- and long-term performance. Results supported the contention that this dose level, when administered during early training, produces long-term enhancement of problem solving.