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Evidence for the involvment
of 5-hydroxytryptamine in inter-temporal choice «Inter-temporal choice» refers to choice between smaller immediate gains and larger delayed gains. A synthesis of current theoretical models of inter-temporal choice, the multiplicative hyperbolic model of choice, will be presented. It is assumed that the value of a positive reinforcer increases as a hyperbolic function of its size, and decreases as hyperbolic functions of its delay. Each function contains a single discounting parameter which quantifies the organism’s sensitivity to the variable in question. The hyperbolic functions combine multiplicatively to determine the overall value of the reinforcer. The model gives rise to a quantitative methodology for studying inter-temporal choice, based on linear equations describing performance under conditions of indifference, when the values of the reinforcers are assumed to be equal. We have used this methodology to evaluate the effect of central 5-hydroxytryptamine (5-HT) depletion, induced by microinjection of 5,7-dihydroxytryptamine into the median and dorsal raphe nuclei, on inter-temporal choice. Rats were trained under an adjusting delay schedule to choose between a small food reinforcer delivered after a short delay and a larger reinforcer delivered after longer delays. The length of the short delay was varied in different phases of the experiment, and in each case, the indifference delay to the larger reinforcer was measured. 5-HT-depleted rats showed shorter indifference delays than did sham-lesioned control animals, implicating central 5-HTergic function in the regulation of inter-temporal choice. Keywords: inter-temporal choice, impulsiveness, self-control, delay of reinforcement, 5-HT |
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