University of Kansas, USA.
J Exp Anal Behav. 2012 May;97(3):305-21. doi: 10.1901/jeab.2012.97-305.
Lewis rats have been shown to make more impulsive choices than Fischer 344 rats in discrete-trial choice procedures that arrange fixed (i.e., nontitrating) reinforcement parameters. However, nontitrating procedures yield only gross estimates of preference, as choice measures in animal subjects are rarely graded at the level of the individual subject. The present study was designed to examine potential strain differences in delay discounting using an adjusting-amount procedure, in which distributed (rather than exclusive) choice is observed due to dynamic titration of reinforcer magnitude across trials. Using a steady-state version of the adjusting-amount procedure in which delay was manipulated between experimental conditions, steeper delay discounting was observed in Lewis rats compared to Fischer 344 rats; further, delay discounting in both strains was well described by the traditional hyperbolic discounting model. However, upon partial completion of the present study, a study published elsewhere (Wilhelm & Mitchell, 2009) demonstrated no difference in delay discounting between these strains with the use of a more rapid version of the adjusting-amount procedure (i.e., in which delay is manipulated daily). Thus, following completion of the steady-state assessment in the present study, all surviving Lewis and Fischer 344 rats completed an approximation of this rapid-determination procedure in which no strain difference in delay discounting was observed.
在离散试验选择程序中，与 Fischer 344 大鼠相比，Lewis 大鼠表现出更多的冲动选择，这些程序安排固定（即非滴定）的强化参数。然而，非滴定程序仅产生偏好的粗略估计，因为动物受试者的选择措施很少在个体受试者的水平上分级。本研究旨在使用调整量程序检查潜在的品系差异，在该程序中，由于在试验过程中对强化量进行动态滴定，因此观察到分布式（而不是排他性）选择。使用调整量程序的稳态版本，在实验条件之间操纵延迟，与 Fischer 344 大鼠相比，Lewis 大鼠表现出更陡峭的延迟折扣；此外，两种品系的延迟折扣都很好地由传统的双曲线折扣模型描述。然而，在本研究的部分完成后，另一项发表在别处的研究（Wilhelm 和 Mitchell，2009）表明，在使用调整量程序的更快版本（即每天操纵延迟）时，这些品系之间没有延迟折扣的差异。因此，在本研究的稳态评估完成后，所有幸存的 Lewis 和 Fischer 344 大鼠都完成了对该快速确定程序的近似，在该程序中没有观察到延迟折扣的品系差异。
