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reward which will follow the drinking or drug taking behaviour, thus stressing the importance of cognitive factors in dependence. He argues that only by the recognition of cognitive mediating variables are we able to explain the way that avoidance behaviour is not extinguished; having initially viewed tolerance and withdrawal as a component of dependence he has subsequently claimed that “neuroadaptation has no relevance to dependence unless it is motivational in some way” (Stockwell 1990 p.195). Drawing on the work of Siegel (1988) who showed that physiological changes, specifically tolerance to the repeated administration of morphine in rats can be environmentally influenced, Stockwell argues that the connection between the neuroadaptive state and the learning process is best understood as the organism’s anticipatory response to the effect of the drug. As described in the opponent process theory of Solomon and Corbit (1974), the action of a drug is opposed by compensatory adaptive responses which come to be classically conditioned to drug taking cues. These compensatory classically conditioned responses can then be triggered by any cue, either internal or environmental that leads the subject to anticipate that drug use is imminent. The drive experienced by the individual in such a situation, to take the drug or to take more of the drug, sometimes construed as craving, will enhance the learning process by the reward, in the form of positive or negative reinforcement, that follows. Equally the fact that tolerance may have been environmentally conditioned as well as having been a physiological consequence of previous use, will result in the individual desiring a greater dose of the drug in order to achieve the same effect. Siegel showed the role played by the environment in the conditioning process in a study in which tolerance to morphine, developed in rats in one environment, did not generalise to an unfamiliar environment thus demonstrating that the dose of the morphine alone did not account for the degree of tolerance developed.
Further in support of the cognitive components of conditioning is the evidence for the relativity of reinforcement; different drugs may have different reinforcement potential based upon their potency, speed of onset, pathoplasticity and elimination half-life (Raistrick et al. 1994) but their reinforcement potential is none the less mediated by the availability to the individual of other sources of reinforcement. This relativity of the reinforcement potential of different drugs is determined by the individual’s expectations of the rewards of drug taking relative to other activities. It may however be the case that what Logan has described as the uniquely potent reinforcement potential of addictive drugs (Logan 1993) is what lies behind the observation and inclusion in dependence definitions of the ‘narrowing of the drug taking repertoire’ or the ‘stereotyping of drug taking behaviour’; at higher levels of dependence the potency of pharmacological and physiological rewards is greater than the potency of other rewards, for example social rewards. Item scores for the
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