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PhD Thesis - Topp, L.

The nature of amphetamine dependence syndrome
Topp, L. (1998)

Abstract:
There is a lack of consensus on the existence of amphetamine dependence, and little explication of the motivational factors underlying dependent use. This thesis examined the applicability to amphetamine of the dominant contemporary conception of drug dependence, the drug dependence syndrome (DDS; Edwards, Arif & Hodgson, 1981). It also examined the applicability of the dominant psychological explanations of dependence, with an emphasis on those couched in terms of positive and negative reinforcement. The first study validated the only questionnaire to specifically assess amphetamine dependence, which showed good psychometric properties and discriminatory power. This questionnaire concentrated almost exclusively on the negative reinforcement capacity of amphetamine. Therefore, the second study also assessed positive reinforcement, demonstrating its importance in motivating amphetamine use among those located across the continuum of dependence. Negative reinforcement was also important among more severely dependent users. The third study employed experimental methodology to test the hypotheses of reinforcement models which emphasise the contribution of classical conditioning to drug dependence. Currently dependent amphetamine users exhibited significant increases in amphetamine-related responses following presentation of an amphetamine-related cue, changes which were not observed in nondependent controls. However, the results failed to support one dominant model of conditioning to the exclusion of all others, leaving open the question of the appropriateness of this framework to examine the contributions of positive and negative reinforcement to dependence. The fourth study demonstrated that amphetamine dependence as assessed by a structured interview providing DSM-III-R diagnoses is consistent with the hypotheses of Edwards et al. (1981): the dependence criteria demonstrated an underlying unidimensional structure, and every criterion, physiological, behavioural and psychological, was important in defining the dependence syndrome for this drug. The final study found that a shorter and more comprehensible instrument than that operationalising DSM-III-R could be used to screen for amphetamine dependence with little loss of diagnostic information. This thesis has demonstrated that, firstly, a unidimensional dependence syndrome is applicable to amphetamine; and, secondly, that positive reinforcement is important to amphetamine users located across the continuum of dependence, whereas among those with more severe dependence, negative reinforcement also perpetuates continued use.

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