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- Title
Effect of central 5-hydroxytryptamine depletion on inter-temporal choice: a quantitative analysis.
- Authors
Mobini, S.; Chiang, T.-J.; Al-Ruwaitea, A. S. A.; Ho, M.-Y.; Bradshaw, C. M.; Szabadi, E.
- Abstract
Abstract Rationale: It has been proposed that the ascending 5-hydroxytryptaminergic (5-HTergic) pathways are involved in "impulse control". Previous experiments have shown that rats whose 5-HTergic pathways have been destroyed are more liable than intact rats to select a smaller, immediate reinforcer rather than a larger, delayed reinforcer (impulsive choice). However, it remains unclear whether this effect of central 5-HT depletion reflects a change in the rate of time discounting (i.e. a change in the rate at which reinforcers become devalued as a function of delay) or a change in sensitivity to reinforcer size. Objective: We examined the effect of central 5-HT depletion on time discounting using a quantitative model of inter-temporal choice (multiplicative hyperbolic model), which enables effects on time discounting to be differentiated from effects on sensitivity to reinforcer size. Methods: Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press two levers for food-pellet reinforcers in a discrete-trials adjusting-delay schedule. In free-choice trials, selection of lever A resulted in a brief fixed delay (d[sub A]) followed by delivery of one pellet; selection of lever B resulted in a longer variable delay (d[sub B]) followed by delivery of two pellets; d[sub B] was adjusted in accordance with the subject's choices. The value of d[sub A] was varied (0.5-8.0 s) in successive phases of the experiment, and the indifference value of d[sub B] was determined in each case. Results: In both groups, the indifference value of d[sub B] was linearly related to the value of d[sub A], in accordance with the multiplicative hyperbolic model. The lesioned group showed shorter indifference delays than the sham-lesioned group, this being reflected in a parallel displacement of the linear indifference function. In both experiments, the levels of 5HT and 5-hydroxyindole-acetic acid were reduced in the
- Subjects
IMPULSE control disorders; OPERANT behavior; REINFORCEMENT (Psychology)
- Publication
Psychopharmacology, 2000, Vol 149, Issue 3, p313
- ISSN
0033-3158
- Publication type
Article
- DOI
10.1007/s002130000385