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Reprinted from M.A. Bozarth (1987) (Ed.), Methods of assessing the reinforcing properties of abused drugs (pp. v-vi). New York: Springer-Verlag.
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Drug abuse is a major health problem affecting increasingly larger segments of society. Statistics regarding heroin addiction show that the number of addicts has remained stable for the past decade, but data regarding the use of cocaine reveal a current epidemic with over 5 million Americansdemic with over 5 million Americans using cocaine on a regular basis. With the increased availability of new, less expensive forms of cocaine accompanied by a change in the route of administration (i.e., increased number of people smoking cocaine) and by a change in the social acceptability of its recreational use, a continued rise in cocaine addiction is expected throughout this decade. In addition, there are pronounced cyclic variations in the incidence of abusing other drugs such as phencyclidine, methaqualone, and diazepam.

Traditional views of drug abuse have focused on a variety of factors ranging from genetic to psychodynamic theories. Attempts have been made both to explain drug addiction case-by-case (i.e., develop special theories for each class of abused drug) and to formulate a unifying theory that would include a wide variety of drug classes. The opioids have long been studied as a prototypical class of addictive drugs, and early work focused on the physiological dependence produced by the repeated administration of these drugs. This research provided the basis for one of the first theories that attempted to explain addiction to several classes of drugs based on a single variable--addiction to opioids, ethanol, and barbiturates are all accompanied by strong signs of physiological dependence, and drug-taking behavior was suggested to evolve from the ability of these drugs to abate the withdrawal discomfort associated with abstinence. This theory, emphasizing the physiological dependence produced by these drugs, was very important because it focused on empirical (and not psychodynamic) factors involved in drug addiction.

In the 1960s three major developments helped shape the current view of drug addiction. First, definitions of drug addiction shifted from emphasis on physiological dependence to emphasis on the drug-taking behavior itself. That is, it was recognized that the defining characteristic of an addiction is not the development of physiological dependence but rather the development of compulsive drug-taking behavior. Second, specific psychometric scales were developed to quantify the subjective effects of abusedantify the subjective effects of abused drugs (e.g., the Addiction Research Center Inventory), and considerable attention focused on the mood altering properties of these drugs. This revealed that a number of addictive drugs share an ability to elevate mood and produce "pleasant" affective changes. Third, experimental techniques were developed that permit studying drug self-administration in laboratory animals. These animals are presumed not to suffer from any predisposing psychological tendencies (e.g., addictive personalities, psychoneuroses), and operant conditioning paradigms have shown that an animal’s behavior can be controlled by addictive drugs in much the same manner that food or water can control the behavior of a hungry or thirsty animal. These three factors led to a reassessment of traditional views of drug addiction and helped develop a more empirically oriented, scientific perspective for studying drug addiction.

Considerable research during the past two decades has focused on studying the reinforcing properties of abused drugs. This has led to the development of a number of techniques for assessing drug reward. Many of the procedures involve directly measuring the reinforcing property of a drug (e.g., drug self-administration in both laboratory animals and humans), while other methods study a variety of factors that appear to correspond to drug reinforcement (e.g., subjective effects in humans and drug discrimination ins in humans and drug discrimination in animals). The study of drug reinforcement contributes not only to the screening of new compounds for addiction liability but also to a basic understanding of drug addiction. In addition, studying the ability of pharmacological agents to control behavior may reveal important insights into the nature of brain mechanisms underlying basic motivational processes.

The main objective of this book is to create a compendium of the methods currently used to assess drug reinforcement by providing synopses of these diverse procedures in a single reference. Each of the major methods of studying drug reinforcement has been summarized, and applications of these techniques are illustrated. Although the specific applications of these methods may vary, the methodological considerations outlined in this book should provide a lasting framework for interpreting the results of current experimental findings.

A number of people have contributed to the development of this book. First, the participants in the l983 Satellite Symposium held in conjunction with the Society for Neuroscience Meeting in Boston provided the initial encouragement that such a book would make an important contribution to research in this field—the success of the interdisciplinary symposium reinforced the notion that individual researchers could greatly benefit from learning about the work done using different methods to address a common problferent methods to address a common problem. Second, Margaret Hamilton and Jim Dalton are thanked for proof reading sections of the book; the elusive typographical errors and omissions that invariably appear in such a volume have been greatly reduced by their efforts. Finally, the endurance, patience, and editorial skills of Valarie Harlan Bozarth are gratefully acknowledged. The fruit of her commitment to facilitating the presentation of scientific material to a diverse audience can be found throughout the pages of this book.

Support for some phases of manuscript preparation came from grants from the National Institute on Drug Abuse (U.S.A.) and the Natural Sciences and Engineering Research Council (Canada).

Michael A. Bozarth

©1987 Springer-Verlag (printed version)
©2000-2009 Addiction Science Network (web-enhanced version)

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