Effects of <i>d</i>-amphetamine on choice behavior under mixed concurrent schedules
The goals of this dissertation were to conduct detailed analyses of behavior in transition in response to changes in reinforcement contingencies by using mixed concurrent Random Interval-Random Interval (conc RI RI) schedules of reinforcement and to examine the effects of d-amphetamine on behavior in transition. A mixed conc RI RI schedule of reinforcement (MCS) procedure was used with rats to arrange reinforcers for responding across two independent levers. Subjects could vary responding between the two levers. During the initial 30 min of a 3-hour session, the contingencies were equal, after which they changed during some of the sessions. For one-third of sessions, the probability of reinforcement for left lever responding was four times greater than for responding on the right lever. For one-third of sessions, the probability of reinforcement for right lever responding was four times greater than for responding on the left lever. For the remaining one-third of sessions, the probability of reinforcement for responding remained equal across both levers. Terminal reinforcer ratios (left: right) used were 4:1, 1:1, and 1:4. Once responding during transition sessions stabilized over several sessions, saline or d-amphetamine (0.1–6.0 mg/kg) was administered IP 30 min prior to some of the experimental sessions.
Dose-response curves for all rats showed no significant differences in reinforcers obtained before transitions between control, saline, and d-amphetamine sessions, except for at the highest dose of d-amphetamine for which there was typically a decrease. Tabular data revealed a slight peak in reinforcers that corresponded with the dose that increased total reinforcers for that rat. Microanalytic data further revealed more rapid transitions in response proportions after the programmed changes under low to moderate doses, an increase in total responses and visits at low to moderate doses due to more changeovers, and a decrease in response rate and some perseverative responding at higher doses of d-amphetamine, which disrupted performance and resulted in fewer reinforcers.