Department of Behavioral Sciences, Oslo Metropolitan University, St. Olavs Plass, P.O. Box 4, Oslo, 0130, Norway; School of Health Sciences, Kristiania University College, Chr. Krohgs Gate 32A, Oslo, 0186, Norway.
Departamento de Psicología Básica I, Universidad Nacional de Educación a Distancia (UNED), C/ Juan del Rosal 10, Madrid, 28040, Spain.
Behav Brain Res. 2021 Jun 25;408:113236. doi: 10.1016/j.bbr.2021.113236. Epub 2021 Mar 13.
Delay discounting involves choosing between a small, immediate reward, and a larger but delayed one. As the delay between choice and large reward gets longer, people with ADHD tend to become impulsive faster than controls, indicated by a switch in preference from the large to the smaller reward. Choosing the smaller reward when the larger is considered reward maximizing is labeled impulsive behaviour. It is well documented that increased delays between choice and reward affects choice preference in both humans and other animals. Other variables such as the inter-trial interval or trial length are observed to have an effect on human discounting, but their effect on discounting in other animals is largely assumed rather than tested. In the current experiment, we tested this assumption. One group of rats was exposed to increasing delays between choosing the large reward and receiving it, while another group experienced longer inter-trial intervals that were equal in length to the delays in the other group. This ensured that trial length was controlled for in delay discounting, but that the delay function and inter-trial intervals could be manipulated and measured separately. Results showed that while the delay between choice and reward caused impulsive behaviour in rats, the length of the inter-trial interval (and by extension trial length) had no impact on choice behaviour. A follow-up experiment found this to be the case even if the length of the inter-trial interval was signaled with audio cues. These results suggest that rats, and possibly animals in general, are insensitive to time between trials, and therefore cannot easily represent human counterparts on the task.
延迟折扣涉及在小的、即时奖励和大的但延迟的奖励之间进行选择。随着选择和大奖励之间的延迟时间变长，ADHD 患者往往比对照组更容易变得冲动，表现为从大奖励到小奖励的偏好转变。当较大的奖励被认为是最大化奖励时，选择较小的奖励被标记为冲动行为。大量文献记录表明，选择和奖励之间的延迟增加会影响人类和其他动物的选择偏好。其他变量，如试验间间隔或试验长度，被观察到对人类折扣产生影响，但它们对其他动物折扣的影响在很大程度上是假设的，而不是经过测试的。在当前的实验中，我们检验了这一假设。一组大鼠经历了选择大奖励和获得奖励之间的延迟增加，而另一组大鼠经历了更长的试验间间隔，其长度与另一组大鼠的延迟相等。这确保了在延迟折扣中控制了试验长度，但延迟函数和试验间间隔可以分别进行操纵和测量。结果表明，尽管选择和奖励之间的延迟导致了大鼠的冲动行为，但试验间间隔的长度（以及试验长度）对选择行为没有影响。后续实验发现，即使试验间间隔的长度通过音频提示来指示，情况也是如此。这些结果表明，大鼠，可能还有一般动物，对试验之间的时间不敏感，因此在任务中不能轻易代表人类。
