Dom et al. [1] report on differences in discounting rates between patients with early and late onset of alcoholism. Individuals with early-onset alcoholism discounted delayed rewards more rapidly than their late-onset counterparts, who evidenced discount rates similar to controls. Differences between the groups were also noted with respect to a variety of other self-report indices of impulsivity and sensation seeking. These findings add to the growing literature on discounting rates and substance abuse. Published reports now demonstrate that virtually every substance-abusing population discounts delayed rewards more rapidly than controls. In addition, more and more studies are emerging that examine factors within drug-abusing populations that are related to discounting, such as the effects of drug abstinence or withdrawal [2,3], antisocial personality disorder [4] and severity or multiplicity [5,6] of problems. A study from our laboratory [7] even found that paternal history of alcoholism was related to high discounting rates in non-substance-abusing women. Early onset of alcoholism is related to many of the above factors, including heritability, increased number and severity of substances used and antisocial personality disorder. It is not surprising that this subgroup of early-onset alcoholics discounted more rapidly than late-onset alcoholics, but this study is, nevertheless, a useful demonstration of another factor that relates to discounting. This is an exciting field of research. The first studies of delay discounting were conducted with laboratory animals, and the concept was applied initially to drug dependence in 1997 [8]. Since then, publications on this topic have increased exponentially. Measurement and task features have been refined, but they are not perfected. In fact, counterintuitive data are available demonstrating, for example, reductions in discounting during acute administration of drugs [9]. A report from another group of investigators [10] actually found no differences in discounting rates between early- and late-onset alcohol-dependent patients, although alcohol-dependent patients as a whole did discount more rapidly than controls. The reasons for differences across studies and populations remain to be determined but the overarching theme, that substance abusers evidence increased discounting, remains. Hypotheses related to why this relationship exists are in a nascent stage. Only limited data address discounting and development of substance use problems. Concordance between this measure of impulsivity and other behavioral and personality indices are not well explored, and whether discounting rates uniquely predict substance abuse, or other psychiatric conditions, is unclear. Strong evidence is not yet available that treatment, be it pharmacological or behavioral, can alter the rapid discounting of delayed rewards in drug abusing populations. As more researchers begin and continue to explore delay discounting, perhaps some of these questions can be answered. Further understanding of these issues and their biological, psychological and societal underpinnings may lead ultimately to novel prevention and treatment of drug abuse, and perhaps other impulse control disorders as well.
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Aug 12, 2013
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