Excessive discounting of delayed reinforcers as a trans-disease process contributing to addiction and other disease-related vulnerabilities: emerging evidence

Abstract

Delay discounting describes the devaluation of a reinforcer as a function of the delay until its receipt. Although all people discount delayed reinforcers, one consistent finding is that substance-dependent individuals tend to discount delayed reinforcers more rapidly than do healthy controls. Moreover, these higher-than-normal discounting rates have been observed in individuals with other behavioral maladies such as pathological gambling, poor health behavior, and overeating. This suggests that high rates of delay discounting may be a trans-disease process (i.e., a process that occurs across a range of disorders, making findings from one disorder relevant to other disorders). In this paper, we argue that delay discounting is a trans-disease process, undergirded by an imbalance between two competing neurobehavioral decision systems. Implications for our understanding of, and treatment for, this trans-disease process are discussed.

Figure 1

This figure shows the predicted values of two reinforcers as a function of the delay until their receipt as predicted by the exponential model (left panel, 1a) and hyperbolic model (right panel, 1b). The height of the vertical lines represents the magnitudes of two reinforcers. The relative height of the solid and dashed curves represents preference for the two reinforcers. From Monterosso & Ainslie, 2007.

Figure 2

Sample curves comparing the median discounting rates of a group of opioid dependent individuals to those of healthy controls. The y-axis shows the median indifference points expressed as a percentage of the immediate reinforcer for the opioid dependent (squares) and control (triangles) groups. The x-axis shows the delay until the larger reinforcer. The dashed and solid lines show the hyperbolic functions fit to the data from the opioid-dependent and control groups, respectively. Figure adapted from Madden et al., 1997.