Understanding addiction as a pathology of temporal horizon.

Abstract

The seemingly irrational behavior exhibited by individuals with addiction may be understood by considering their temporal horizon. In this paper, we reviewed published literature and current research concerning how delay discounting, a measure of temporal horizon, has been employed to understand addiction. Specifically, studies of delay discounting among addicted individuals and other psychiatric populations, current controversies in the delay discounting literature, and new developments were reviewed. Addicted individuals discount the long-term consequences of their behavior at a higher rate than matched controls. Current controversies illustrate the need for continued research. Given the rising interest in using delay discounting to understand addictive behaviors, in terms of both overt behavior and at the level of brain activity, we believe research in this field will continue to produce substantial progress for the next several years. Keywords: temporal horizon, delay discounting, impulsivity, neuroeconomics, trait, state ********** Addiction is a serious public health problem that is projected to cost over $245 billion to the US economy annually (NIDA InfoFacts: Costs to Society, 2005). One of the greatest challenges in understanding addiction is the seemingly irrational behavior exhibited by those affected. For example, it is hard to understand why an individual who knows about the risk of contracting a life-threatening disease would choose to use a hypodermic needle that some other individual has just used to inject drugs. We believe that such behavior and other persistent problems among individuals with addiction may be understood by considering their temporal horizon. Consider a study from our group where we asked opioid-dependent individuals and matched controls to complete a story that started: After awakening, Bill began to think about his future. In general, he expected to ... The specific events that each participant used to complete their story were not important. Instead we were interested in the time frame of their story. Opioid-dependent individuals referred to a future of nine days on average, while the controls referred to a future of 4.7 years (Petry, Bickel, & Arnett, 1998). This striking difference becomes a lens by which to view the behavior of the addicted. If one's temporal horizon entails only the next nine days, then considering the long-term consequences of sharing injecting equipment is not relevant because the consequences of those actions fall beyond that temporal view. In that regard, these consequences may be discounted such that they are for all intents and purposes non-existent. Our view is that the seemingly irrational behavior of addicted individuals may be usefully considered as an extreme and continuing constriction of temporal horizon. In this paper, we will review how the behavioral economic concept of delay discounting has been employed to understand addiction. We will then review the extant literature on the discounting behavior among individuals who exhibit addictive behaviors, followed by examination of whether the extreme discounting among addicted individuals is a state or trait, and consideration of whether extreme temporal discounting is reflective of impulsivity or temporal horizon. Finally, we will examine the implications of using discounting to understand addiction in the new scientific field of neuroeconomics. Delay Discounting Discounting of delayed reinforcers refers to the observation that behavioral effects of a reinforcer are modulated by the delay to its receipt (Logue, 1988). Said another way, the value of a delayed reinforcer is discounted (reduced in value or considered to be worth less) compared to the value of an immediate reinforcer. Indeed, discounting of delayed rewards seems intuitive because most individuals would prefer a reinforcer (e.g., $1,000) now rather than that same reinforcer later (Kirby, 1997). …