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theoretically capable of being unlearned. It may exist independently of the physiological and other consequences of substance use and therefore might be extinguished, to the extent that it can be extinguished, independently of the removal of some of the cues that trigger the behaviour. Both clinical and non-clinical observation has supported the idea that dependence, once established in a certain degree of severity, is incapable of extinction. This approach, as discussed earlier, has come to be associated with disease formulations of the condition which, in turn have been associated with folklore rather than science. However, as discussed above, both animal and human studies have highlighted the persistence of dependent behaviour following substantial periods of abstinence suggesting that some learned behaviour may be difficult, even impossible to extinguish. This finding does not detract from the ability of learning theory to explain the phenomenon of dependence as Logan has demonstrated in his review of animal and human motivation and drug use (Logan 1993). It does, however, highlight the need to understand the mechanisms of change if the conditions in which change can occur are to be enhanced.
The psychological formulation of dependence has implications for measurement. Instruments measuring the dependence syndrome are discussed in detail in Chapter 3. The Leeds Dependence Questionnaire was, as described above, based upon the need for an instrument that measured the psychological phenomenon of substance dependence, in other words that measured behavioural and cognitive elements of dependence and would be capable of measuring dependence in abstinence. Instruments that measure the neuroadapted state, or rely heavily on it for measurement purposes, will not be able to measure dependence once a process of withdrawal or detoxification has occurred, whereas an instrument measuring the nature of a person’s relationship with the substance should be able to detect the dependent state that exists during periods of abstinence as well as periods of use. A small scale study to test the Leeds Dependence Questionnaire for use with abstinent respondents, reported in Chapter 4, confirmed its suitability for this purpose. Furthermore, it is proposed that the concept and measurement of substance dependence allows dependence on different substances to be compared for degrees of severity; using the same questionnaire for this purpose implies measuring the same phenomenon regardless of the specific substance being used.
1.7 Formal classification systems
The description and diagnostic criteria of substance dependence and misuse disorders are contained in two major classification systems, the International Statistical Classification of Diseases
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