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still have it; the second was that both morning shakes and their relief are diagnostic of alcohol dependence and the third that they were sufficient criteria to distinguish between moderate and severe dependence. While the first assumption has been demonstrated to be false in that dependence has been shown to be capable of change over time in all directions, the assumptions that withdrawal symptoms and their severity are diagnostic of dependence and the degree of its severity remain the subject of debate. What seems less controversial is that the severity of dependence is determined by the strength of a conditioning process: classical and operant conditioning processes provide an explanatory framework for the development and maintenance of dependent behaviour and a number of reviews of the conditioning literature in this field are available (Drummond et al. 1995; Siegel 1988, 1999). Drinking alcohol for example provides both positive reinforcement (the euphorogenic effects) and negative reinforcement (avoidance of the loss or absence of such effects and avoidance of withdrawal symptoms in those who experience these). Thus the effects of the drug are capable of reinforcing drug using behaviour in two sorts of ways. While these sources of reinforcement persist, they may be followed by the development of additional sources of reinforcement which further contribute to the maintenance of the behaviour. If regular use is established, tolerance and withdrawal are likely to follow and themselves come to form part of the conditioning process in becoming cues for use of the substance. The evidence for the role of withdrawal symptoms in conditioning alcohol and drug seeking behaviour by setting up a reaction described as craving has been demonstrated over a considerable period of time (Jellinek 1960 p.42; Isbell 1955) and Siegel (1999) has described eighteenth and nineteenth century writing on the subject.
Recognition of the possibility for craving to be occasioned by the experience of withdrawal symptoms following recent drinking or morphine use was coupled with a description of withdrawal symptoms initiating feelings of craving in the absence of such recent use. Macnish (1834) referred to these as “cravings of the body” and “cravings of the mind” (p. 243) respectively, while Isbell distinguished them as “nonsymbolic” and “symbolic” craving respectively. The recognition of a drive to consume alcohol (or morphine) in the event either of recent use or in the absence of recent use led to a dualism in thinking on the subject, where the two sorts of events were distinguished as being either physical or psychological in nature. Rankin et al. (1979) referred to this dualism as a gross oversimplification (p. 389). They described craving not as an automatic response but as a response to cues of either physiological, psychological or environmental origin, and went on to describe the physiological, subjective and behavioural components of this response.
The phenomenon of craving in the absence of recent use has been explained in a series of studies which have demonstrated the way in which withdrawal symptoms can be conditioned by the
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