Substance Use Disorders A Biopsychosocial Perspective

The brain’s subcortical dopamine circuitry promotes approach and engagement (“go”) but is often opposed by the inhibitory control (“stop”) exerted by the prefrontal cerebral cortex. Addictive drugs effectively engage the “go” system, and the inhibitory control is often deficient in addicted individuals, a result of either heavy drug use or a pre-existing condition. Repeated activation of the “go” circuits causes neuroadaptation that lessens the euphoric drug effects, resulting in withdrawal syndrome and lingering dysphoria when drug use stops. Persistent and compulsive drug-seeking then emerges as reinforcement shifts from predominantly positive and pleasurable, to the negative reinforcement of relief from dysphoria.Drug-seeking behavior is also strengthened as dopamine activation results in conditioning of stimuli predicting drug effects. Increased glutamate activity promotes development of incentive sensitization, thought to underlie the strong response to drug-related stimuli that drive the compulsion for drug use even after the initial rewarding effect is greatly reduced – producing the “wanting, but not liking” dissociation often seen in addiction.