Determinants of choice, and vulnerability and recovery in addiction
Introduction
Addiction is a phenomenon science struggles to both define and treat. Most commonly, the word addiction pertains to the habitual use of licit and illicit substances threatening the individual and society, and these threats may include direct health effects, such as cardiovascular or liver disease, or effects such as loss of employment or social relationships. Prevalence of regular drug use is high in the US; a recent survey indicated that over 21 million Americans, or about 8% of the population meet the criteria for substance abuse or dependence (Substance Abuse and Mental Health Services Administration (SAMHSA), 2014), and the economic burden exceeds several hundred billion dollars annually (National Drug Intelligence Center (NDIC), 2011). Numbers that do not even take into account the almost 1 in 5 American adults who smoke tobacco.
Additionally, addiction is often characterized by compulsions or inability to stop using drugs, despite the individual expressing a desire to stop (see Belin et al., 2016). Health risk, habitual usage, and compulsion have helped identify addiction as a phenomenon, but the responsible processes remain elusive. The prevailing scientific view is of addiction as a brain disease, best understood as a change in molecular, cellular, or circuit mechanisms (Leshner, 1997), a view that contains some face and construct validity. Appealing to changes in brain circuits may help reconcile the continued drug use despite the person’s expressed desire to stop, and certainly, it is difficult to understand how such extensive behavior change could not be accompanied by changes in the brain.
However, an alternative to the conceptualization of addiction as a brain disease has continued to gain momentum; in this view, addiction is not best understood as a brain disease, but as a choice disorder (Heyman, 2009, Vuchinich and Tucker, 1988). The term “choice” has the usual problems inherent in adopting common language to describe behavior (see Chiesa, 1994, Chapter 2; Skinner, 1938 pp. 6–8), especially because this term has such a loaded societal meaning when applied to addiction. In a scientific context, “choice” simply refers to engaging in one activity out of several possibilities. When studying choice the important question is what are the determinants of the relative probabilities of various behaviors, i.e., what are the determinants of choice? Conceptualizing addiction as a choice disorder focuses study on the determinants of drug choice. Proponents of addiction as a choice disorder do not deny the role of molecular or neural processes in the production of behavior. No one would maintain the brain was not involved in behavior nor that biologic factors might bias the choice that occurs in a given circumstance, but again the argument is how to best frame the relevant processes (see also Szasz, 1974). When addiction is viewed as a choice disorder, addiction is the outcome of poor options in the environment, devalued rewards, and/or the ease of access to drugs relative to other goods (see, Heyman, 2009, Hursh and Roma, 2013, Madden and Bickel, 2010, Schaler, 2002, Vuchinich and Tucker, 1988); and how these interact with the history and biology the individual brings to this environment.
The differing views (brain disease vs choice disorder) are not just a matter of perspective, but they lie at the center of how best to study, understand, and ultimately treat addiction. The brain disease conceptualization seeks to understand addiction as the result of brain dysfunction in an otherwise normal world; the choice-disorder conceptualization seeks to understand addiction as normal neural functioning in an otherwise dysfunctional world. In parallel, treatments borne out of the brain disease conceptualization seek to correct dysfunctional circuits, correct imbalanced neurotransmitters, etc., while the choice-disorder view centers on “choosing” as the prima facie focus of treatment. In other words, providing the circumstances for better choices. Contingency management (CM) approaches, for example, have seen wide success in the treatment of substance abuse problems for a variety of drugs (Bigelow and Silverman, 1999, Higgins et al., 1991, Lamb et al., 2010, Petry et al., 2012, Stitzer et al., 1992) by arranging more immediate, tangible reinforcement for abstinence. Among the guiding principles in CM is that delayed outcomes, such as those that follow years of healthy choices, weakly motivate behavior, in contrast to immediate rewards, which are more powerful motivators. Therefore by providing more immediate reward for healthy choices (abstinence), those alternatives may be chosen more frequently.
Continued understanding of the role environmental, genetic, and neural factors play in disorders of choice will require the continued development of sophisticated laboratory models. The purpose of this paper is to review work on some of these pre-clinical models developed in our laboratories. The models grew out of the conceptualization of addiction as a choice-disorder, and they can be used to study processes that may be involved in the vulnerability to and the recovery from addiction. The present conceptualization and the models derived from it may have great translational utility. The remainder of the paper first discusses how individual differences in how the delay to alternative rewards affect behavior may result in individual differences in vulnerability to addiction; and how these processes might be modeled in animals. Next, how recovery can be modeled in animals when addiction is viewed as a choice is discussed. Finally, the paper concludes that conceptualizing addiction as choice is a paradigm that furthers translational research into addiction and is a natural extension of the earlier paradigm shift of conceptualizing addiction as reinforced behavior (Schuster, 1976, Griffiths et al., 1980).
Section snippets
Delay discounting & choice
The consequences of behavior often differ along multiple dimensions, with magnitude and delay being among the most salient. Other things equal, individuals prefer larger rewards over smaller and rewards that are delivered sooner over those that are delivered later (e.g., Catania, 1963, Chung and Herrnstein, 1967). Predicting which options an individual is likely to choose becomes more complicated when these dimensions conflict, for example, when the choice is between a smaller reward delivered
Rapid discounting and risk for addiction
Many studies show that those with substance use problems discount delayed rewards more rapidly than those without these problems. For instance, opioid abusers discount more rapidly than those who do not abuse opioids (Kirby et al., 1999). Similarly, those who abuse cocaine discount more rapidly than those who do not (Heil et al., 2006), and those with problematic alcohol use discount more rapidly than without alcohol problems (Petry, 2002). Finally, people who smoke cigarettes discount more
Discounting in those at risk for addiction
There appears to be two dominant groups of individuals at risk for addiction and both appear to discount rapidly. Many individuals in their adolescence and young adulthood engage in dangerous substance use and other risky behavior outside the norms of older individuals (Substance Abuse and Mental Health Services Administration (SAMHSA), 2009, Moffitt, 1993). This risky behavior, however, declines as adult roles are taken on (Moffitt, 1993). There are parallel developmental trends in delay
Modeling recovery
Recovery from addiction can also be viewed within the conceptualization of choice. In this case, several strategies for reducing drug choice are apparent. First, one could reduce the effectiveness of drug at reinforcing behavior, and several pre-clinical studies have used choice procedures to study medications that might attenuate drug reinforcement (Ginsburg and Lamb, 2014, Negus, 2005, Weiss et al., 1990). Another commonly used clinical strategy is the differential reinforcement of other
Conclusions
Addiction may be conceptualized as a choice disorder (e.g. Heyman, 2009), and this perspective may be modeled in the laboratory and explicitly tested Several of the models, from among many, that can be used to examine the utility and validity of this conceptualization were reviewed in this paper. Such models may suggest new research questions or ways of understanding addiction. These, new questions or understandings provide ways of assessing the utility and veracity of the conceptualization and
Acknowledgements
This work was supported by R01 AA012337 (RJL), T32 DA031115 (DRM), R01 AA016987 (BCG), K05 DA17918 (CPF) and R01 DA029254 (CPF).
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