ABSTRACT
Modern, non-invasive neuroimaging provides, for the first time, a vehicle to address questions about the acute effects of drugs of abuse on the human brain, the consequences of their chronic use and ultimately the mechanisms leading to the development of drug dependence and addiction. Contrary to popular belief, addiction is not defined by physical dependence on a drug but by the lack of control over drug intake, i.e. the compulsive use of a drug against one’s will and at the expense of other behaviors.1 Hence, addicts often report continued drug self-administration despite the absence of its ability to produce an acute pleasurable feeling and, instead, having considerable adverse physical, personal and financial consequences.1 Recent theories argue that drug addiction involves neuroadaptive, plastic brain mechanisms driving the transition from casual, recreational drug taking to a regular, compulsive habit.2,3 While it has been argued that certain individuals may have an innate predisposition to developing a drug addiction,3,4 it has been difficult to isolate specific differences in brain neurochemistry [e.g. numbers of dopamine (DA) receptors or transporters] responsible for this predisposition, since comparison of drug addicts to healthy, non-drug users is confounded by the effects of chronic drug use on the brain. This problem of trait (innate) versus state (induced) causes of differences in brain structure and function also plagues many other areas of brain imaging research in psychiatry. However, these alternatives can potentially be disentangled by examining the time course of drug effects on the brain in experiments employing both drug-naïve and experienced animals, and by studying healthy control subjects showing certain addictive tendencies.
