The role of impulsivity in the development and maintenance of drug addiction

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Drug addiction is characterised both by compulsion to take the drug and loss of control in limiting drug intake.  Most researchers agree that compulsive drug use develops because brain dopamine systems become sensitised with repeated drug exposure.  In contrast, little is known about the brain changes that mediate impulsive or uncontrolled drug-taking.  Our research examines the relationship between impulsivity and drug addiction, using established animal models of this disorder.  Impulsivity in humans is associated with reductions in serotonin levels and damage to the prefrontal cortex.  Addicts show abnormalities in both systems, leading to the hypothesis that chronic drug abuse produces neural changes that increase impulsivity and lead to further drug use.  Surprisingly, our previous work demonstrates that long-term exposure to cocaine produces minimal effects on impulsivity, although it does alter serotonin mechanisms in the prefrontal cortex.  We now propose to investigate whether these effects are more pronounced in adolescence, a period characterized by impulsivity, increased vulnerability to addiction and dramatic developmental changes in the prefrontal cortex.  We will also examine whether impulsivity in addiction and other psychiatric disorders, including binge eating disorder, represent the same phenomenon.  Binge eating disorder is similar to drug addiction in that it is characterized by uncontrolled (i.e., disinhibited) intake of highly palatable (i.e., rewarding) food.  And, like drug addiction, it is not clear why this aberrant behaviour develops.  Our work may shed light on the mechanisms (biological and environmental) that increase this behaviour.  In the long term, our research may help to eliminate, or even reverse, the potentially tragic consequences of impulsive behaviours associated with drug addiction.  Moreover, understanding the contingencies controlling behaviour in both drugged and undrugged states may ultimately lead to the development of novel therapies to treat addiction.