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Drug addiction: bad habits add up
Trevor W. Robbins and Barry J. Everitt
We know how many drugs of abuse — cocaine, heroin and nicotine — work, but less about how they lead to addiction. Studies of the brain-learning systems concerned are addressing the causes of addiction, with the intent of developing better treatments.
rug addiction — which is increasingly seen as a neuropsychiatric disorder — places an enormous burden on society through its repercussions on crime rate and healthcare. The economic costs of addiction have been estimated at 80 billion dollars in the United States alone, and many Western countries have invested heavily in research towards understanding, treating and preventing addiction. Recently, through genetic and cell-biological approaches, many of the molecular targets for drugs of abuse have been identified and cloned. But the value of these powerful reductionist approaches depends, in turn, on an integrative framework of systems and cognitive neuroscience. Such a framework allows us to formulate new hypotheses that take into account the complex factors influencing addiction and its treatment.
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shown to be associated with reduced levels of dopamine in the nucleus accumbens4. From these observations comes the ‘modal hypothesis’, which states that the reinforcing effects of all drugs of abuse partly depend on the mesolimbic dopamine system. These effects could, perhaps, stem from the more general role of this system in mediating the motivating properties of natural stimuli such as food or sex. In some sense, then, drugs ‘short-circuit’ or ‘usurp’ normal behavioural and motivational processes mediated by this region of the brain1. But although there is compelling evidence that amphetamine-like stimulants interact with this circuitry, the ‘strong’ form of the dopamine hypothesis — which embraces all other drugs of abuse — is certainly not universally accepted. For example, opiates...