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the mechanism of classical conditioning. Childress and her colleagues found that methadone dependent subjects experienced a variety of conditioned responses to stimuli that had previously been associated with drug use, including craving in the absence of withdrawal symptoms, withdrawal symptoms with no accompanying craving and a combination of both withdrawal symptoms and the experience of craving (Childress et al. 1986).
Meyer and Mirin (1979) showed that cognitive mediating factors play an important role: heroin users experienced increased craving during periods when heroin was available for self administration; those who were aware of the blocking effects of the opiate antagonist, naltrexone, did not experience increased craving in the presence of heroin related stimuli when they were pre-treated with naltrexone, presumably because they knew they would not be able to experience the euphorigenic effects. These authors described the way in which naltrexone changed the perception of the environment into one where heroin was unavailable.
An understanding of the cognitive and conditioning mechanisms involved in the development and maintenance of dependent behaviour may be relevant to an understanding the nature of change in substance dependence and will be discussed in the next chapter.
The idea of substance dependence, dependence which crosses substance boundaries, departs from the dependence syndrome by replacing physiological markers (of tolerance and withdrawal) with behavioural markers (of pursuit and avoidance) and thus is referred to as a psychological formulation of the concept; however it departs also from the broader psychological view of dependence stated by Russell (1976) and Orford (1985) which embraces such objects of dependence as people and activities. Russell’s definition focused upon the presence of negative affect in the absence of the object of dependence and upon the degree of difficulty experienced in doing without that object (Russell 1971). Thus he described dependence as existing in degrees from the normal to the pathological, and his view was that the question of when dependence becomes a problem is one of culture specific definition; often dependence will only become apparent through its consequences. Pharmacological rewards were just one class of reinforcer alongside other equally potentially important sources of reinforcement. Orford (1985) added to this idea of dependence the crucial feature of conflict which is the result of the development of a strong attachment to the behaviour: the result of its repeated reinforcement in the face of longer term negative consequences. Marks (1990), using the term addiction rather than dependence and developing a yet more embracing definition, referred to the commonalities between behavioural addictions in which he included obsessive-compulsive disorder alongside kleptomania, compulsive gambling, hypersexuality and overeating. He does however refer to separate syndromes in order
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