Discounting of Delayed Food and Water in Rats

Humans often make decisions between outcomes that occur at different times. For example, students may have to decide whether to study to get a good grade on a test tomorrow or hang out with friends tonight. One of the ways we describe how people make these decisions is called delay discounting. Delay discounting is the decline in present value of an outcome because of its delay. Thus, students might prefer hanging out with friends now over a good grade because getting a good grade occurs later and is less valuable. The study of delay discounting is important because a preference for smaller-sooner outcomes over larger-later outcomes (i.e., steep delay discounting) is associated with problematic behavior such as substance abuse. To understand this process better, we can study delay discounting in non-human animals such as rats. For example, we might record whether a rat prefers a small amount of food now or a larger amount of food later. However, these procedures may not be realistic to human decisions because when rats make the choice for the larger-later food they are forced to wait through the delay. Humans, however, can change their mind while they are waiting for delayed outcomes. For example, when an individual commits to stop smoking cigarettes for the long-term health benefits, they have the option to begin smoking again. Thus, we compared two delay discounting tasks in rats. In one task, rats could defect on their choice for the larger, later outcome. In the other task they were forced to wait through the delay. We found that when the rats were given the option to defect on their choice, they waited for the outcomes without defecting. In addition, we found that even when given the option to defect, rats made similar choices across both tasks