Fig. 5.

Facilitation of PR performance following systemic administration of d-amphetamine. a Administration of 1 mg/kg d-amphetamine significantly increases breakpoints in both schedule groups. Breakpoints are significantly higher in the PREXP group relative to rats reinforced under the PR4 schedule following administration of 1 mg/kg amphetamine. b The duration of the mean post reinforcement pause (PRP) is significantly reduced by 1 mg/kg amphetamine, in both reinforcement schedule conditions. c Enhancement of response rates following administration of amphetamine in rats reinforced with the PR4 schedule. d Response rates are enhanced following administration of amphetamine in rats reinforced with the PREXP schedule. e Amphetamine significantly reduces the predicted peak response rate in animals reinforced under the PREXP schedule only. The decay rate of responding is significantly reduced in rats in both schedule groups. Error bars represent ±1 SEM. *p < .05; **p < .01